# orm/session.py # Copyright (C) 2005-2019 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Provides the Session class and related utilities.""" import itertools import sys import weakref from . import attributes from . import exc from . import identity from . import loading from . import persistence from . import query from . import state as statelib from .base import _class_to_mapper from .base import _none_set from .base import _state_mapper from .base import instance_str from .base import object_mapper from .base import object_state from .base import state_str from .deprecated_interfaces import SessionExtension from .unitofwork import UOWTransaction from .. import engine from .. import exc as sa_exc from .. import sql from .. import util from ..inspection import inspect from ..sql import expression from ..sql import util as sql_util __all__ = ["Session", "SessionTransaction", "SessionExtension", "sessionmaker"] _sessions = weakref.WeakValueDictionary() """Weak-referencing dictionary of :class:`.Session` objects. """ def _state_session(state): """Given an :class:`.InstanceState`, return the :class:`.Session` associated, if any. """ if state.session_id: try: return _sessions[state.session_id] except KeyError: pass return None class _SessionClassMethods(object): """Class-level methods for :class:`.Session`, :class:`.sessionmaker`.""" @classmethod @util.deprecated( "1.3", "The :meth:`.Session.close_all` method is deprecated and will be " "removed in a future release. Please refer to " ":func:`.session.close_all_sessions`.", ) def close_all(cls): """Close *all* sessions in memory.""" close_all_sessions() @classmethod @util.dependencies("sqlalchemy.orm.util") def identity_key(cls, orm_util, *args, **kwargs): """Return an identity key. This is an alias of :func:`.util.identity_key`. """ return orm_util.identity_key(*args, **kwargs) @classmethod def object_session(cls, instance): """Return the :class:`.Session` to which an object belongs. This is an alias of :func:`.object_session`. """ return object_session(instance) ACTIVE = util.symbol("ACTIVE") PREPARED = util.symbol("PREPARED") COMMITTED = util.symbol("COMMITTED") DEACTIVE = util.symbol("DEACTIVE") CLOSED = util.symbol("CLOSED") class SessionTransaction(object): """A :class:`.Session`-level transaction. :class:`.SessionTransaction` is a mostly behind-the-scenes object not normally referenced directly by application code. It coordinates among multiple :class:`.Connection` objects, maintaining a database transaction for each one individually, committing or rolling them back all at once. It also provides optional two-phase commit behavior which can augment this coordination operation. The :attr:`.Session.transaction` attribute of :class:`.Session` refers to the current :class:`.SessionTransaction` object in use, if any. The :attr:`.SessionTransaction.parent` attribute refers to the parent :class:`.SessionTransaction` in the stack of :class:`.SessionTransaction` objects. If this attribute is ``None``, then this is the top of the stack. If non-``None``, then this :class:`.SessionTransaction` refers either to a so-called "subtransaction" or a "nested" transaction. A "subtransaction" is a scoping concept that demarcates an inner portion of the outermost "real" transaction. A nested transaction, which is indicated when the :attr:`.SessionTransaction.nested` attribute is also True, indicates that this :class:`.SessionTransaction` corresponds to a SAVEPOINT. **Life Cycle** A :class:`.SessionTransaction` is associated with a :class:`.Session` in its default mode of ``autocommit=False`` immediately, associated with no database connections. As the :class:`.Session` is called upon to emit SQL on behalf of various :class:`.Engine` or :class:`.Connection` objects, a corresponding :class:`.Connection` and associated :class:`.Transaction` is added to a collection within the :class:`.SessionTransaction` object, becoming one of the connection/transaction pairs maintained by the :class:`.SessionTransaction`. The start of a :class:`.SessionTransaction` can be tracked using the :meth:`.SessionEvents.after_transaction_create` event. The lifespan of the :class:`.SessionTransaction` ends when the :meth:`.Session.commit`, :meth:`.Session.rollback` or :meth:`.Session.close` methods are called. At this point, the :class:`.SessionTransaction` removes its association with its parent :class:`.Session`. A :class:`.Session` that is in ``autocommit=False`` mode will create a new :class:`.SessionTransaction` to replace it immediately, whereas a :class:`.Session` that's in ``autocommit=True`` mode will remain without a :class:`.SessionTransaction` until the :meth:`.Session.begin` method is called. The end of a :class:`.SessionTransaction` can be tracked using the :meth:`.SessionEvents.after_transaction_end` event. **Nesting and Subtransactions** Another detail of :class:`.SessionTransaction` behavior is that it is capable of "nesting". This means that the :meth:`.Session.begin` method can be called while an existing :class:`.SessionTransaction` is already present, producing a new :class:`.SessionTransaction` that temporarily replaces the parent :class:`.SessionTransaction`. When a :class:`.SessionTransaction` is produced as nested, it assigns itself to the :attr:`.Session.transaction` attribute, and it additionally will assign the previous :class:`.SessionTransaction` to its :attr:`.Session.parent` attribute. The behavior is effectively a stack, where :attr:`.Session.transaction` refers to the current head of the stack, and the :attr:`.SessionTransaction.parent` attribute allows traversal up the stack until :attr:`.SessionTransaction.parent` is ``None``, indicating the top of the stack. When the scope of :class:`.SessionTransaction` is ended via :meth:`.Session.commit` or :meth:`.Session.rollback`, it restores its parent :class:`.SessionTransaction` back onto the :attr:`.Session.transaction` attribute. The purpose of this stack is to allow nesting of :meth:`.Session.rollback` or :meth:`.Session.commit` calls in context with various flavors of :meth:`.Session.begin`. This nesting behavior applies to when :meth:`.Session.begin_nested` is used to emit a SAVEPOINT transaction, and is also used to produce a so-called "subtransaction" which allows a block of code to use a begin/rollback/commit sequence regardless of whether or not its enclosing code block has begun a transaction. The :meth:`.flush` method, whether called explicitly or via autoflush, is the primary consumer of the "subtransaction" feature, in that it wishes to guarantee that it works within in a transaction block regardless of whether or not the :class:`.Session` is in transactional mode when the method is called. Note that the flush process that occurs within the "autoflush" feature as well as when the :meth:`.Session.flush` method is used **always** creates a :class:`.SessionTransaction` object. This object is normally a subtransaction, unless the :class:`.Session` is in autocommit mode and no transaction exists at all, in which case it's the outermost transaction. Any event-handling logic or other inspection logic needs to take into account whether a :class:`.SessionTransaction` is the outermost transaction, a subtransaction, or a "nested" / SAVEPOINT transaction. .. seealso:: :meth:`.Session.rollback` :meth:`.Session.commit` :meth:`.Session.begin` :meth:`.Session.begin_nested` :attr:`.Session.is_active` :meth:`.SessionEvents.after_transaction_create` :meth:`.SessionEvents.after_transaction_end` :meth:`.SessionEvents.after_commit` :meth:`.SessionEvents.after_rollback` :meth:`.SessionEvents.after_soft_rollback` """ _rollback_exception = None def __init__(self, session, parent=None, nested=False): self.session = session self._connections = {} self._parent = parent self.nested = nested self._state = ACTIVE if not parent and nested: raise sa_exc.InvalidRequestError( "Can't start a SAVEPOINT transaction when no existing " "transaction is in progress" ) if self.session._enable_transaction_accounting: self._take_snapshot() self.session.dispatch.after_transaction_create(self.session, self) @property def parent(self): """The parent :class:`.SessionTransaction` of this :class:`.SessionTransaction`. If this attribute is ``None``, indicates this :class:`.SessionTransaction` is at the top of the stack, and corresponds to a real "COMMIT"/"ROLLBACK" block. If non-``None``, then this is either a "subtransaction" or a "nested" / SAVEPOINT transaction. If the :attr:`.SessionTransaction.nested` attribute is ``True``, then this is a SAVEPOINT, and if ``False``, indicates this a subtransaction. .. versionadded:: 1.0.16 - use ._parent for previous versions """ return self._parent nested = False """Indicates if this is a nested, or SAVEPOINT, transaction. When :attr:`.SessionTransaction.nested` is True, it is expected that :attr:`.SessionTransaction.parent` will be True as well. """ @property def is_active(self): return self.session is not None and self._state is ACTIVE def _assert_active( self, prepared_ok=False, rollback_ok=False, deactive_ok=False, closed_msg="This transaction is closed", ): if self._state is COMMITTED: raise sa_exc.InvalidRequestError( "This session is in 'committed' state; no further " "SQL can be emitted within this transaction." ) elif self._state is PREPARED: if not prepared_ok: raise sa_exc.InvalidRequestError( "This session is in 'prepared' state; no further " "SQL can be emitted within this transaction." ) elif self._state is DEACTIVE: if not deactive_ok and not rollback_ok: if self._rollback_exception: raise sa_exc.InvalidRequestError( "This Session's transaction has been rolled back " "due to a previous exception during flush." " To begin a new transaction with this Session, " "first issue Session.rollback()." " Original exception was: %s" % self._rollback_exception, code="7s2a", ) elif not deactive_ok: raise sa_exc.InvalidRequestError( "This session is in 'inactive' state, due to the " "SQL transaction being rolled back; no further " "SQL can be emitted within this transaction." ) elif self._state is CLOSED: raise sa_exc.ResourceClosedError(closed_msg) @property def _is_transaction_boundary(self): return self.nested or not self._parent def connection(self, bindkey, execution_options=None, **kwargs): self._assert_active() bind = self.session.get_bind(bindkey, **kwargs) return self._connection_for_bind(bind, execution_options) def _begin(self, nested=False): self._assert_active() return SessionTransaction(self.session, self, nested=nested) def _iterate_self_and_parents(self, upto=None): current = self result = () while current: result += (current,) if current._parent is upto: break elif current._parent is None: raise sa_exc.InvalidRequestError( "Transaction %s is not on the active transaction list" % (upto) ) else: current = current._parent return result def _take_snapshot(self): if not self._is_transaction_boundary: self._new = self._parent._new self._deleted = self._parent._deleted self._dirty = self._parent._dirty self._key_switches = self._parent._key_switches return if not self.session._flushing: self.session.flush() self._new = weakref.WeakKeyDictionary() self._deleted = weakref.WeakKeyDictionary() self._dirty = weakref.WeakKeyDictionary() self._key_switches = weakref.WeakKeyDictionary() def _restore_snapshot(self, dirty_only=False): """Restore the restoration state taken before a transaction began. Corresponds to a rollback. """ assert self._is_transaction_boundary to_expunge = set(self._new).union(self.session._new) self.session._expunge_states(to_expunge, to_transient=True) for s, (oldkey, newkey) in self._key_switches.items(): # we probably can do this conditionally based on # if we expunged or not, but safe_discard does that anyway self.session.identity_map.safe_discard(s) # restore the old key s.key = oldkey # now restore the object, but only if we didn't expunge if s not in to_expunge: self.session.identity_map.replace(s) for s in set(self._deleted).union(self.session._deleted): self.session._update_impl(s, revert_deletion=True) assert not self.session._deleted for s in self.session.identity_map.all_states(): if not dirty_only or s.modified or s in self._dirty: s._expire(s.dict, self.session.identity_map._modified) def _remove_snapshot(self): """Remove the restoration state taken before a transaction began. Corresponds to a commit. """ assert self._is_transaction_boundary if not self.nested and self.session.expire_on_commit: for s in self.session.identity_map.all_states(): s._expire(s.dict, self.session.identity_map._modified) statelib.InstanceState._detach_states( list(self._deleted), self.session ) self._deleted.clear() elif self.nested: self._parent._new.update(self._new) self._parent._dirty.update(self._dirty) self._parent._deleted.update(self._deleted) self._parent._key_switches.update(self._key_switches) def _connection_for_bind(self, bind, execution_options): self._assert_active() if bind in self._connections: if execution_options: util.warn( "Connection is already established for the " "given bind; execution_options ignored" ) return self._connections[bind][0] if self._parent: conn = self._parent._connection_for_bind(bind, execution_options) if not self.nested: return conn else: if isinstance(bind, engine.Connection): conn = bind if conn.engine in self._connections: raise sa_exc.InvalidRequestError( "Session already has a Connection associated for the " "given Connection's Engine" ) else: conn = bind._contextual_connect() if execution_options: conn = conn.execution_options(**execution_options) if self.session.twophase and self._parent is None: transaction = conn.begin_twophase() elif self.nested: transaction = conn.begin_nested() else: transaction = conn.begin() self._connections[conn] = self._connections[conn.engine] = ( conn, transaction, conn is not bind, ) self.session.dispatch.after_begin(self.session, self, conn) return conn def prepare(self): if self._parent is not None or not self.session.twophase: raise sa_exc.InvalidRequestError( "'twophase' mode not enabled, or not root transaction; " "can't prepare." ) self._prepare_impl() def _prepare_impl(self): self._assert_active() if self._parent is None or self.nested: self.session.dispatch.before_commit(self.session) stx = self.session.transaction if stx is not self: for subtransaction in stx._iterate_self_and_parents(upto=self): subtransaction.commit() if not self.session._flushing: for _flush_guard in range(100): if self.session._is_clean(): break self.session.flush() else: raise exc.FlushError( "Over 100 subsequent flushes have occurred within " "session.commit() - is an after_flush() hook " "creating new objects?" ) if self._parent is None and self.session.twophase: try: for t in set(self._connections.values()): t[1].prepare() except: with util.safe_reraise(): self.rollback() self._state = PREPARED def commit(self): self._assert_active(prepared_ok=True) if self._state is not PREPARED: self._prepare_impl() if self._parent is None or self.nested: for t in set(self._connections.values()): t[1].commit() self._state = COMMITTED self.session.dispatch.after_commit(self.session) if self.session._enable_transaction_accounting: self._remove_snapshot() self.close() return self._parent def rollback(self, _capture_exception=False): self._assert_active(prepared_ok=True, rollback_ok=True) stx = self.session.transaction if stx is not self: for subtransaction in stx._iterate_self_and_parents(upto=self): subtransaction.close() boundary = self rollback_err = None if self._state in (ACTIVE, PREPARED): for transaction in self._iterate_self_and_parents(): if transaction._parent is None or transaction.nested: try: for t in set(transaction._connections.values()): t[1].rollback() transaction._state = DEACTIVE self.session.dispatch.after_rollback(self.session) except: rollback_err = sys.exc_info() finally: transaction._state = DEACTIVE if self.session._enable_transaction_accounting: transaction._restore_snapshot( dirty_only=transaction.nested ) boundary = transaction break else: transaction._state = DEACTIVE sess = self.session if ( not rollback_err and sess._enable_transaction_accounting and not sess._is_clean() ): # if items were added, deleted, or mutated # here, we need to re-restore the snapshot util.warn( "Session's state has been changed on " "a non-active transaction - this state " "will be discarded." ) boundary._restore_snapshot(dirty_only=boundary.nested) self.close() if self._parent and _capture_exception: self._parent._rollback_exception = sys.exc_info()[1] if rollback_err: util.reraise(*rollback_err) sess.dispatch.after_soft_rollback(sess, self) return self._parent def close(self, invalidate=False): self.session.transaction = self._parent if self._parent is None: for connection, transaction, autoclose in set( self._connections.values() ): if invalidate: connection.invalidate() if autoclose: connection.close() else: transaction.close() self._state = CLOSED self.session.dispatch.after_transaction_end(self.session, self) if self._parent is None: if not self.session.autocommit: self.session.begin() self.session = None self._connections = None def __enter__(self): return self def __exit__(self, type_, value, traceback): self._assert_active(deactive_ok=True, prepared_ok=True) if self.session.transaction is None: return if type_ is None: try: self.commit() except: with util.safe_reraise(): self.rollback() else: self.rollback() class Session(_SessionClassMethods): """Manages persistence operations for ORM-mapped objects. The Session's usage paradigm is described at :doc:`/orm/session`. """ public_methods = ( "__contains__", "__iter__", "add", "add_all", "begin", "begin_nested", "close", "commit", "connection", "delete", "execute", "expire", "expire_all", "expunge", "expunge_all", "flush", "get_bind", "is_modified", "bulk_save_objects", "bulk_insert_mappings", "bulk_update_mappings", "merge", "query", "refresh", "rollback", "scalar", ) @util.deprecated_params( weak_identity_map=( "1.0", "The :paramref:`.Session.weak_identity_map` parameter as well as " "the strong-referencing identity map are deprecated, and will be " "removed in a future release. For the use case where objects " "present in a :class:`.Session` need to be automatically strong " "referenced, see the recipe at " ":ref:`session_referencing_behavior` for an event-based approach " "to maintaining strong identity references. ", ), _enable_transaction_accounting=( "0.7", "The :paramref:`.Session._enable_transaction_accounting` " "parameter is deprecated and will be removed in a future release.", ), extension=( "0.7", ":class:`.SessionExtension` is deprecated in favor of the " ":class:`.SessionEvents` listener interface. The " ":paramref:`.Session.extension` parameter will be " "removed in a future release.", ), ) def __init__( self, bind=None, autoflush=True, expire_on_commit=True, _enable_transaction_accounting=True, autocommit=False, twophase=False, weak_identity_map=None, binds=None, extension=None, enable_baked_queries=True, info=None, query_cls=None, ): r"""Construct a new Session. See also the :class:`.sessionmaker` function which is used to generate a :class:`.Session`-producing callable with a given set of arguments. :param autocommit: .. warning:: The autocommit flag is **not for general use**, and if it is used, queries should only be invoked within the span of a :meth:`.Session.begin` / :meth:`.Session.commit` pair. Executing queries outside of a demarcated transaction is a legacy mode of usage, and can in some cases lead to concurrent connection checkouts. Defaults to ``False``. When ``True``, the :class:`.Session` does not keep a persistent transaction running, and will acquire connections from the engine on an as-needed basis, returning them immediately after their use. Flushes will begin and commit (or possibly rollback) their own transaction if no transaction is present. When using this mode, the :meth:`.Session.begin` method is used to explicitly start transactions. .. seealso:: :ref:`session_autocommit` :param autoflush: When ``True``, all query operations will issue a :meth:`~.Session.flush` call to this ``Session`` before proceeding. This is a convenience feature so that :meth:`~.Session.flush` need not be called repeatedly in order for database queries to retrieve results. It's typical that ``autoflush`` is used in conjunction with ``autocommit=False``. In this scenario, explicit calls to :meth:`~.Session.flush` are rarely needed; you usually only need to call :meth:`~.Session.commit` (which flushes) to finalize changes. :param bind: An optional :class:`.Engine` or :class:`.Connection` to which this ``Session`` should be bound. When specified, all SQL operations performed by this session will execute via this connectable. :param binds: A dictionary which may specify any number of :class:`.Engine` or :class:`.Connection` objects as the source of connectivity for SQL operations on a per-entity basis. The keys of the dictionary consist of any series of mapped classes, arbitrary Python classes that are bases for mapped classes, :class:`.Table` objects and :class:`.Mapper` objects. The values of the dictionary are then instances of :class:`.Engine` or less commonly :class:`.Connection` objects. Operations which proceed relative to a particular mapped class will consult this dictionary for the closest matching entity in order to determine which :class:`.Engine` should be used for a particular SQL operation. The complete heuristics for resolution are described at :meth:`.Session.get_bind`. Usage looks like:: Session = sessionmaker(binds={ SomeMappedClass: create_engine('postgresql://engine1'), SomeDeclarativeBase: create_engine('postgresql://engine2'), some_mapper: create_engine('postgresql://engine3'), some_table: create_engine('postgresql://engine4'), }) .. seealso:: :ref:`session_partitioning` :meth:`.Session.bind_mapper` :meth:`.Session.bind_table` :meth:`.Session.get_bind` :param \class_: Specify an alternate class other than ``sqlalchemy.orm.session.Session`` which should be used by the returned class. This is the only argument that is local to the :class:`.sessionmaker` function, and is not sent directly to the constructor for ``Session``. :param enable_baked_queries: defaults to ``True``. A flag consumed by the :mod:`sqlalchemy.ext.baked` extension to determine if "baked queries" should be cached, as is the normal operation of this extension. When set to ``False``, all caching is disabled, including baked queries defined by the calling application as well as those used internally. Setting this flag to ``False`` can significantly reduce memory use, however will also degrade performance for those areas that make use of baked queries (such as relationship loaders). Additionally, baked query logic in the calling application or potentially within the ORM that may be malfunctioning due to cache key collisions or similar can be flagged by observing if this flag resolves the issue. .. versionadded:: 1.2 :param _enable_transaction_accounting: A legacy-only flag which when ``False`` disables *all* 0.5-style object accounting on transaction boundaries. :param expire_on_commit: Defaults to ``True``. When ``True``, all instances will be fully expired after each :meth:`~.commit`, so that all attribute/object access subsequent to a completed transaction will load from the most recent database state. :param extension: An optional :class:`~.SessionExtension` instance, or a list of such instances, which will receive pre- and post- commit and flush events, as well as a post-rollback event. :param info: optional dictionary of arbitrary data to be associated with this :class:`.Session`. Is available via the :attr:`.Session.info` attribute. Note the dictionary is copied at construction time so that modifications to the per- :class:`.Session` dictionary will be local to that :class:`.Session`. .. versionadded:: 0.9.0 :param query_cls: Class which should be used to create new Query objects, as returned by the :meth:`~.Session.query` method. Defaults to :class:`.Query`. :param twophase: When ``True``, all transactions will be started as a "two phase" transaction, i.e. using the "two phase" semantics of the database in use along with an XID. During a :meth:`~.commit`, after :meth:`~.flush` has been issued for all attached databases, the :meth:`~.TwoPhaseTransaction.prepare` method on each database's :class:`.TwoPhaseTransaction` will be called. This allows each database to roll back the entire transaction, before each transaction is committed. :param weak_identity_map: Defaults to ``True`` - when set to ``False``, objects placed in the :class:`.Session` will be strongly referenced until explicitly removed or the :class:`.Session` is closed. """ if weak_identity_map in (True, None): self._identity_cls = identity.WeakInstanceDict else: self._identity_cls = identity.StrongInstanceDict self.identity_map = self._identity_cls() self._new = {} # InstanceState->object, strong refs object self._deleted = {} # same self.bind = bind self.__binds = {} self._flushing = False self._warn_on_events = False self.transaction = None self.hash_key = _new_sessionid() self.autoflush = autoflush self.autocommit = autocommit self.expire_on_commit = expire_on_commit self.enable_baked_queries = enable_baked_queries self._enable_transaction_accounting = _enable_transaction_accounting self.twophase = twophase self._query_cls = query_cls if query_cls else query.Query if info: self.info.update(info) if extension: for ext in util.to_list(extension): SessionExtension._adapt_listener(self, ext) if binds is not None: for key, bind in binds.items(): self._add_bind(key, bind) if not self.autocommit: self.begin() _sessions[self.hash_key] = self connection_callable = None transaction = None """The current active or inactive :class:`.SessionTransaction`.""" @util.memoized_property def info(self): """A user-modifiable dictionary. The initial value of this dictionary can be populated using the ``info`` argument to the :class:`.Session` constructor or :class:`.sessionmaker` constructor or factory methods. The dictionary here is always local to this :class:`.Session` and can be modified independently of all other :class:`.Session` objects. .. versionadded:: 0.9.0 """ return {} def begin(self, subtransactions=False, nested=False): """Begin a transaction on this :class:`.Session`. .. warning:: The :meth:`.Session.begin` method is part of a larger pattern of use with the :class:`.Session` known as **autocommit mode**. This is essentially a **legacy mode of use** and is not necessary for new applications. The :class:`.Session` normally handles the work of "begin" transparently, which in turn relies upon the Python DBAPI to transparently "begin" transactions; there is **no need to explicitly begin transactions** when using modern :class:`.Session` programming patterns. In its default mode of ``autocommit=False``, the :class:`.Session` does all of its work within the context of a transaction, so as soon as you call :meth:`.Session.commit`, the next transaction is implicitly started when the next database operation is invoked. See :ref:`session_autocommit` for further background. The method will raise an error if this :class:`.Session` is already inside of a transaction, unless :paramref:`~.Session.begin.subtransactions` or :paramref:`~.Session.begin.nested` are specified. A "subtransaction" is essentially a code embedding pattern that does not affect the transactional state of the database connection unless a rollback is emitted, in which case the whole transaction is rolled back. For documentation on subtransactions, please see :ref:`session_subtransactions`. :param subtransactions: if True, indicates that this :meth:`~.Session.begin` can create a "subtransaction". :param nested: if True, begins a SAVEPOINT transaction and is equivalent to calling :meth:`~.Session.begin_nested`. For documentation on SAVEPOINT transactions, please see :ref:`session_begin_nested`. :return: the :class:`.SessionTransaction` object. Note that :class:`.SessionTransaction` acts as a Python context manager, allowing :meth:`.Session.begin` to be used in a "with" block. See :ref:`session_autocommit` for an example. .. seealso:: :ref:`session_autocommit` :meth:`.Session.begin_nested` """ if self.transaction is not None: if subtransactions or nested: self.transaction = self.transaction._begin(nested=nested) else: raise sa_exc.InvalidRequestError( "A transaction is already begun. Use " "subtransactions=True to allow subtransactions." ) else: self.transaction = SessionTransaction(self, nested=nested) return self.transaction # needed for __enter__/__exit__ hook def begin_nested(self): """Begin a "nested" transaction on this Session, e.g. SAVEPOINT. The target database(s) and associated drivers must support SQL SAVEPOINT for this method to function correctly. For documentation on SAVEPOINT transactions, please see :ref:`session_begin_nested`. :return: the :class:`.SessionTransaction` object. Note that :class:`.SessionTransaction` acts as a context manager, allowing :meth:`.Session.begin_nested` to be used in a "with" block. See :ref:`session_begin_nested` for a usage example. .. seealso:: :ref:`session_begin_nested` :ref:`pysqlite_serializable` - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly. """ return self.begin(nested=True) def rollback(self): """Rollback the current transaction in progress. If no transaction is in progress, this method is a pass-through. This method rolls back the current transaction or nested transaction regardless of subtransactions being in effect. All subtransactions up to the first real transaction are closed. Subtransactions occur when :meth:`.begin` is called multiple times. .. seealso:: :ref:`session_rollback` """ if self.transaction is None: pass else: self.transaction.rollback() def commit(self): """Flush pending changes and commit the current transaction. If no transaction is in progress, this method raises an :exc:`~sqlalchemy.exc.InvalidRequestError`. By default, the :class:`.Session` also expires all database loaded state on all ORM-managed attributes after transaction commit. This so that subsequent operations load the most recent data from the database. This behavior can be disabled using the ``expire_on_commit=False`` option to :class:`.sessionmaker` or the :class:`.Session` constructor. If a subtransaction is in effect (which occurs when begin() is called multiple times), the subtransaction will be closed, and the next call to ``commit()`` will operate on the enclosing transaction. When using the :class:`.Session` in its default mode of ``autocommit=False``, a new transaction will be begun immediately after the commit, but note that the newly begun transaction does *not* use any connection resources until the first SQL is actually emitted. .. seealso:: :ref:`session_committing` """ if self.transaction is None: if not self.autocommit: self.begin() else: raise sa_exc.InvalidRequestError("No transaction is begun.") self.transaction.commit() def prepare(self): """Prepare the current transaction in progress for two phase commit. If no transaction is in progress, this method raises an :exc:`~sqlalchemy.exc.InvalidRequestError`. Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an :exc:`~sqlalchemy.exc.InvalidRequestError` is raised. """ if self.transaction is None: if not self.autocommit: self.begin() else: raise sa_exc.InvalidRequestError("No transaction is begun.") self.transaction.prepare() def connection( self, mapper=None, clause=None, bind=None, close_with_result=False, execution_options=None, **kw ): r"""Return a :class:`.Connection` object corresponding to this :class:`.Session` object's transactional state. If this :class:`.Session` is configured with ``autocommit=False``, either the :class:`.Connection` corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the :class:`.Connection` returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted). Alternatively, if this :class:`.Session` is configured with ``autocommit=True``, an ad-hoc :class:`.Connection` is returned using :meth:`.Engine.connect` on the underlying :class:`.Engine`. Ambiguity in multi-bind or unbound :class:`.Session` objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the :meth:`.get_bind` method for resolution. :param bind: Optional :class:`.Engine` to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over ``mapper``, ``clause``. :param mapper: Optional :func:`.mapper` mapped class, used to identify the appropriate bind. This argument takes precedence over ``clause``. :param clause: A :class:`.ClauseElement` (i.e. :func:`~.sql.expression.select`, :func:`~.sql.expression.text`, etc.) which will be used to locate a bind, if a bind cannot otherwise be identified. :param close_with_result: Passed to :meth:`.Engine.connect`, indicating the :class:`.Connection` should be considered "single use", automatically closing when the first result set is closed. This flag only has an effect if this :class:`.Session` is configured with ``autocommit=True`` and does not already have a transaction in progress. :param execution_options: a dictionary of execution options that will be passed to :meth:`.Connection.execution_options`, **when the connection is first procured only**. If the connection is already present within the :class:`.Session`, a warning is emitted and the arguments are ignored. .. versionadded:: 0.9.9 .. seealso:: :ref:`session_transaction_isolation` :param \**kw: Additional keyword arguments are sent to :meth:`get_bind()`, allowing additional arguments to be passed to custom implementations of :meth:`get_bind`. """ if bind is None: bind = self.get_bind(mapper, clause=clause, **kw) return self._connection_for_bind( bind, close_with_result=close_with_result, execution_options=execution_options, ) def _connection_for_bind(self, engine, execution_options=None, **kw): if self.transaction is not None: return self.transaction._connection_for_bind( engine, execution_options ) else: conn = engine._contextual_connect(**kw) if execution_options: conn = conn.execution_options(**execution_options) return conn def execute(self, clause, params=None, mapper=None, bind=None, **kw): r"""Execute a SQL expression construct or string statement within the current transaction. Returns a :class:`.ResultProxy` representing results of the statement execution, in the same manner as that of an :class:`.Engine` or :class:`.Connection`. E.g.:: result = session.execute( user_table.select().where(user_table.c.id == 5) ) :meth:`~.Session.execute` accepts any executable clause construct, such as :func:`~.sql.expression.select`, :func:`~.sql.expression.insert`, :func:`~.sql.expression.update`, :func:`~.sql.expression.delete`, and :func:`~.sql.expression.text`. Plain SQL strings can be passed as well, which in the case of :meth:`.Session.execute` only will be interpreted the same as if it were passed via a :func:`~.expression.text` construct. That is, the following usage:: result = session.execute( "SELECT * FROM user WHERE id=:param", {"param":5} ) is equivalent to:: from sqlalchemy import text result = session.execute( text("SELECT * FROM user WHERE id=:param"), {"param":5} ) The second positional argument to :meth:`.Session.execute` is an optional parameter set. Similar to that of :meth:`.Connection.execute`, whether this is passed as a single dictionary, or a list of dictionaries, determines whether the DBAPI cursor's ``execute()`` or ``executemany()`` is used to execute the statement. An INSERT construct may be invoked for a single row:: result = session.execute( users.insert(), {"id": 7, "name": "somename"}) or for multiple rows:: result = session.execute(users.insert(), [ {"id": 7, "name": "somename7"}, {"id": 8, "name": "somename8"}, {"id": 9, "name": "somename9"} ]) The statement is executed within the current transactional context of this :class:`.Session`. The :class:`.Connection` which is used to execute the statement can also be acquired directly by calling the :meth:`.Session.connection` method. Both methods use a rule-based resolution scheme in order to determine the :class:`.Connection`, which in the average case is derived directly from the "bind" of the :class:`.Session` itself, and in other cases can be based on the :func:`.mapper` and :class:`.Table` objects passed to the method; see the documentation for :meth:`.Session.get_bind` for a full description of this scheme. The :meth:`.Session.execute` method does *not* invoke autoflush. The :class:`.ResultProxy` returned by the :meth:`.Session.execute` method is returned with the "close_with_result" flag set to true; the significance of this flag is that if this :class:`.Session` is autocommitting and does not have a transaction-dedicated :class:`.Connection` available, a temporary :class:`.Connection` is established for the statement execution, which is closed (meaning, returned to the connection pool) when the :class:`.ResultProxy` has consumed all available data. This applies *only* when the :class:`.Session` is configured with autocommit=True and no transaction has been started. :param clause: An executable statement (i.e. an :class:`.Executable` expression such as :func:`.expression.select`) or string SQL statement to be executed. :param params: Optional dictionary, or list of dictionaries, containing bound parameter values. If a single dictionary, single-row execution occurs; if a list of dictionaries, an "executemany" will be invoked. The keys in each dictionary must correspond to parameter names present in the statement. :param mapper: Optional :func:`.mapper` or mapped class, used to identify the appropriate bind. This argument takes precedence over ``clause`` when locating a bind. See :meth:`.Session.get_bind` for more details. :param bind: Optional :class:`.Engine` to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over ``mapper`` and ``clause`` when locating a bind. :param \**kw: Additional keyword arguments are sent to :meth:`.Session.get_bind()` to allow extensibility of "bind" schemes. .. seealso:: :ref:`sqlexpression_toplevel` - Tutorial on using Core SQL constructs. :ref:`connections_toplevel` - Further information on direct statement execution. :meth:`.Connection.execute` - core level statement execution method, which is :meth:`.Session.execute` ultimately uses in order to execute the statement. """ clause = expression._literal_as_text( clause, allow_coercion_to_text=True ) if bind is None: bind = self.get_bind(mapper, clause=clause, **kw) return self._connection_for_bind(bind, close_with_result=True).execute( clause, params or {} ) def scalar(self, clause, params=None, mapper=None, bind=None, **kw): """Like :meth:`~.Session.execute` but return a scalar result.""" return self.execute( clause, params=params, mapper=mapper, bind=bind, **kw ).scalar() def close(self): """Close this Session. This clears all items and ends any transaction in progress. If this session were created with ``autocommit=False``, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed. """ self._close_impl(invalidate=False) def invalidate(self): """Close this Session, using connection invalidation. This is a variant of :meth:`.Session.close` that will additionally ensure that the :meth:`.Connection.invalidate` method will be called on all :class:`.Connection` objects. This can be called when the database is known to be in a state where the connections are no longer safe to be used. E.g.:: try: sess = Session() sess.add(User()) sess.commit() except gevent.Timeout: sess.invalidate() raise except: sess.rollback() raise This clears all items and ends any transaction in progress. If this session were created with ``autocommit=False``, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed. .. versionadded:: 0.9.9 """ self._close_impl(invalidate=True) def _close_impl(self, invalidate): self.expunge_all() if self.transaction is not None: for transaction in self.transaction._iterate_self_and_parents(): transaction.close(invalidate) def expunge_all(self): """Remove all object instances from this ``Session``. This is equivalent to calling ``expunge(obj)`` on all objects in this ``Session``. """ all_states = self.identity_map.all_states() + list(self._new) self.identity_map = self._identity_cls() self._new = {} self._deleted = {} statelib.InstanceState._detach_states(all_states, self) def _add_bind(self, key, bind): try: insp = inspect(key) except sa_exc.NoInspectionAvailable: if not isinstance(key, type): raise sa_exc.ArgumentError( "Not an acceptable bind target: %s" % key ) else: self.__binds[key] = bind else: if insp.is_selectable: self.__binds[insp] = bind elif insp.is_mapper: self.__binds[insp.class_] = bind for selectable in insp._all_tables: self.__binds[selectable] = bind else: raise sa_exc.ArgumentError( "Not an acceptable bind target: %s" % key ) def bind_mapper(self, mapper, bind): """Associate a :class:`.Mapper` or arbitrary Python class with a "bind", e.g. an :class:`.Engine` or :class:`.Connection`. The given entity is added to a lookup used by the :meth:`.Session.get_bind` method. :param mapper: a :class:`.Mapper` object, or an instance of a mapped class, or any Python class that is the base of a set of mapped classes. :param bind: an :class:`.Engine` or :class:`.Connection` object. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_table` """ self._add_bind(mapper, bind) def bind_table(self, table, bind): """Associate a :class:`.Table` with a "bind", e.g. an :class:`.Engine` or :class:`.Connection`. The given :class:`.Table` is added to a lookup used by the :meth:`.Session.get_bind` method. :param table: a :class:`.Table` object, which is typically the target of an ORM mapping, or is present within a selectable that is mapped. :param bind: an :class:`.Engine` or :class:`.Connection` object. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_mapper` """ self._add_bind(table, bind) def get_bind(self, mapper=None, clause=None): """Return a "bind" to which this :class:`.Session` is bound. The "bind" is usually an instance of :class:`.Engine`, except in the case where the :class:`.Session` has been explicitly bound directly to a :class:`.Connection`. For a multiply-bound or unbound :class:`.Session`, the ``mapper`` or ``clause`` arguments are used to determine the appropriate bind to return. Note that the "mapper" argument is usually present when :meth:`.Session.get_bind` is called via an ORM operation such as a :meth:`.Session.query`, each individual INSERT/UPDATE/DELETE operation within a :meth:`.Session.flush`, call, etc. The order of resolution is: 1. if mapper given and session.binds is present, locate a bind based first on the mapper in use, then on the mapped class in use, then on any base classes that are present in the ``__mro__`` of the mapped class, from more specific superclasses to more general. 2. if clause given and session.binds is present, locate a bind based on :class:`.Table` objects found in the given clause present in session.binds. 3. if session.bind is present, return that. 4. if clause given, attempt to return a bind linked to the :class:`.MetaData` ultimately associated with the clause. 5. if mapper given, attempt to return a bind linked to the :class:`.MetaData` ultimately associated with the :class:`.Table` or other selectable to which the mapper is mapped. 6. No bind can be found, :exc:`~sqlalchemy.exc.UnboundExecutionError` is raised. Note that the :meth:`.Session.get_bind` method can be overridden on a user-defined subclass of :class:`.Session` to provide any kind of bind resolution scheme. See the example at :ref:`session_custom_partitioning`. :param mapper: Optional :func:`.mapper` mapped class or instance of :class:`.Mapper`. The bind can be derived from a :class:`.Mapper` first by consulting the "binds" map associated with this :class:`.Session`, and secondly by consulting the :class:`.MetaData` associated with the :class:`.Table` to which the :class:`.Mapper` is mapped for a bind. :param clause: A :class:`.ClauseElement` (i.e. :func:`~.sql.expression.select`, :func:`~.sql.expression.text`, etc.). If the ``mapper`` argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a :class:`.Table` associated with bound :class:`.MetaData`. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_mapper` :meth:`.Session.bind_table` """ if mapper is clause is None: if self.bind: return self.bind else: raise sa_exc.UnboundExecutionError( "This session is not bound to a single Engine or " "Connection, and no context was provided to locate " "a binding." ) if mapper is not None: try: mapper = inspect(mapper) except sa_exc.NoInspectionAvailable: if isinstance(mapper, type): raise exc.UnmappedClassError(mapper) else: raise if self.__binds: if mapper: for cls in mapper.class_.__mro__: if cls in self.__binds: return self.__binds[cls] if clause is None: clause = mapper.persist_selectable if clause is not None: for t in sql_util.find_tables(clause, include_crud=True): if t in self.__binds: return self.__binds[t] if self.bind: return self.bind if isinstance(clause, sql.expression.ClauseElement) and clause.bind: return clause.bind if mapper and mapper.persist_selectable.bind: return mapper.persist_selectable.bind context = [] if mapper is not None: context.append("mapper %s" % mapper) if clause is not None: context.append("SQL expression") raise sa_exc.UnboundExecutionError( "Could not locate a bind configured on %s or this Session" % (", ".join(context)) ) def query(self, *entities, **kwargs): """Return a new :class:`.Query` object corresponding to this :class:`.Session`.""" return self._query_cls(entities, self, **kwargs) @property @util.contextmanager def no_autoflush(self): """Return a context manager that disables autoflush. e.g.:: with session.no_autoflush: some_object = SomeClass() session.add(some_object) # won't autoflush some_object.related_thing = session.query(SomeRelated).first() Operations that proceed within the ``with:`` block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed. """ autoflush = self.autoflush self.autoflush = False try: yield self finally: self.autoflush = autoflush def _autoflush(self): if self.autoflush and not self._flushing: try: self.flush() except sa_exc.StatementError as e: # note we are reraising StatementError as opposed to # raising FlushError with "chaining" to remain compatible # with code that catches StatementError, IntegrityError, # etc. e.add_detail( "raised as a result of Query-invoked autoflush; " "consider using a session.no_autoflush block if this " "flush is occurring prematurely" ) util.raise_from_cause(e) def refresh( self, instance, attribute_names=None, with_for_update=None, lockmode=None, ): """Expire and refresh the attributes on the given instance. A query will be issued to the database and all attributes will be refreshed with their current database value. Lazy-loaded relational attributes will remain lazily loaded, so that the instance-wide refresh operation will be followed immediately by the lazy load of that attribute. Eagerly-loaded relational attributes will eagerly load within the single refresh operation. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction - usage of :meth:`~Session.refresh` usually only makes sense if non-ORM SQL statement were emitted in the ongoing transaction, or if autocommit mode is turned on. :param attribute_names: optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed. :param with_for_update: optional boolean ``True`` indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of :meth:`.Query.with_for_update`. Supersedes the :paramref:`.Session.refresh.lockmode` parameter. .. versionadded:: 1.2 :param lockmode: Passed to the :class:`~sqlalchemy.orm.query.Query` as used by :meth:`~sqlalchemy.orm.query.Query.with_lockmode`. Superseded by :paramref:`.Session.refresh.with_for_update`. .. seealso:: :ref:`session_expire` - introductory material :meth:`.Session.expire` :meth:`.Session.expire_all` """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._expire_state(state, attribute_names) if with_for_update == {}: raise sa_exc.ArgumentError( "with_for_update should be the boolean value " "True, or a dictionary with options. " "A blank dictionary is ambiguous." ) if lockmode: with_for_update = query.LockmodeArg.parse_legacy_query(lockmode) elif with_for_update is not None: if with_for_update is True: with_for_update = query.LockmodeArg() elif with_for_update: with_for_update = query.LockmodeArg(**with_for_update) else: with_for_update = None if ( loading.load_on_ident( self.query(object_mapper(instance)), state.key, refresh_state=state, with_for_update=with_for_update, only_load_props=attribute_names, ) is None ): raise sa_exc.InvalidRequestError( "Could not refresh instance '%s'" % instance_str(instance) ) def expire_all(self): """Expires all persistent instances within this Session. When any attributes on a persistent instance is next accessed, a query will be issued using the :class:`.Session` object's current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction. To expire individual objects and individual attributes on those objects, use :meth:`Session.expire`. The :class:`.Session` object's default behavior is to expire all state whenever the :meth:`Session.rollback` or :meth:`Session.commit` methods are called, so that new state can be loaded for the new transaction. For this reason, calling :meth:`Session.expire_all` should not be needed when autocommit is ``False``, assuming the transaction is isolated. .. seealso:: :ref:`session_expire` - introductory material :meth:`.Session.expire` :meth:`.Session.refresh` """ for state in self.identity_map.all_states(): state._expire(state.dict, self.identity_map._modified) def expire(self, instance, attribute_names=None): """Expire the attributes on an instance. Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the :class:`.Session` object's current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction. To expire all objects in the :class:`.Session` simultaneously, use :meth:`Session.expire_all`. The :class:`.Session` object's default behavior is to expire all state whenever the :meth:`Session.rollback` or :meth:`Session.commit` methods are called, so that new state can be loaded for the new transaction. For this reason, calling :meth:`Session.expire` only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction. :param instance: The instance to be refreshed. :param attribute_names: optional list of string attribute names indicating a subset of attributes to be expired. .. seealso:: :ref:`session_expire` - introductory material :meth:`.Session.expire` :meth:`.Session.refresh` """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._expire_state(state, attribute_names) def _expire_state(self, state, attribute_names): self._validate_persistent(state) if attribute_names: state._expire_attributes(state.dict, attribute_names) else: # pre-fetch the full cascade since the expire is going to # remove associations cascaded = list( state.manager.mapper.cascade_iterator("refresh-expire", state) ) self._conditional_expire(state) for o, m, st_, dct_ in cascaded: self._conditional_expire(st_) def _conditional_expire(self, state): """Expire a state if persistent, else expunge if pending""" if state.key: state._expire(state.dict, self.identity_map._modified) elif state in self._new: self._new.pop(state) state._detach(self) @util.deprecated( "0.7", "The :meth:`.Session.prune` method is deprecated along with " ":paramref:`.Session.weak_identity_map`. This method will be " "removed in a future release.", ) def prune(self): """Remove unreferenced instances cached in the identity map. Note that this method is only meaningful if "weak_identity_map" is set to False. The default weak identity map is self-pruning. Removes any object in this Session's identity map that is not referenced in user code, modified, new or scheduled for deletion. Returns the number of objects pruned. """ return self.identity_map.prune() def expunge(self, instance): """Remove the `instance` from this ``Session``. This will free all internal references to the instance. Cascading will be applied according to the *expunge* cascade rule. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) if state.session_id is not self.hash_key: raise sa_exc.InvalidRequestError( "Instance %s is not present in this Session" % state_str(state) ) cascaded = list( state.manager.mapper.cascade_iterator("expunge", state) ) self._expunge_states([state] + [st_ for o, m, st_, dct_ in cascaded]) def _expunge_states(self, states, to_transient=False): for state in states: if state in self._new: self._new.pop(state) elif self.identity_map.contains_state(state): self.identity_map.safe_discard(state) self._deleted.pop(state, None) elif self.transaction: # state is "detached" from being deleted, but still present # in the transaction snapshot self.transaction._deleted.pop(state, None) statelib.InstanceState._detach_states( states, self, to_transient=to_transient ) def _register_persistent(self, states): """Register all persistent objects from a flush. This is used both for pending objects moving to the persistent state as well as already persistent objects. """ pending_to_persistent = self.dispatch.pending_to_persistent or None for state in states: mapper = _state_mapper(state) # prevent against last minute dereferences of the object obj = state.obj() if obj is not None: instance_key = mapper._identity_key_from_state(state) if ( _none_set.intersection(instance_key[1]) and not mapper.allow_partial_pks or _none_set.issuperset(instance_key[1]) ): raise exc.FlushError( "Instance %s has a NULL identity key. If this is an " "auto-generated value, check that the database table " "allows generation of new primary key values, and " "that the mapped Column object is configured to " "expect these generated values. Ensure also that " "this flush() is not occurring at an inappropriate " "time, such as within a load() event." % state_str(state) ) if state.key is None: state.key = instance_key elif state.key != instance_key: # primary key switch. use safe_discard() in case another # state has already replaced this one in the identity # map (see test/orm/test_naturalpks.py ReversePKsTest) self.identity_map.safe_discard(state) if state in self.transaction._key_switches: orig_key = self.transaction._key_switches[state][0] else: orig_key = state.key self.transaction._key_switches[state] = ( orig_key, instance_key, ) state.key = instance_key # there can be an existing state in the identity map # that is replaced when the primary keys of two instances # are swapped; see test/orm/test_naturalpks.py -> test_reverse self.identity_map.replace(state) state._orphaned_outside_of_session = False statelib.InstanceState._commit_all_states( ((state, state.dict) for state in states), self.identity_map ) self._register_altered(states) if pending_to_persistent is not None: for state in states.intersection(self._new): pending_to_persistent(self, state.obj()) # remove from new last, might be the last strong ref for state in set(states).intersection(self._new): self._new.pop(state) def _register_altered(self, states): if self._enable_transaction_accounting and self.transaction: for state in states: if state in self._new: self.transaction._new[state] = True else: self.transaction._dirty[state] = True def _remove_newly_deleted(self, states): persistent_to_deleted = self.dispatch.persistent_to_deleted or None for state in states: if self._enable_transaction_accounting and self.transaction: self.transaction._deleted[state] = True if persistent_to_deleted is not None: # get a strong reference before we pop out of # self._deleted obj = state.obj() self.identity_map.safe_discard(state) self._deleted.pop(state, None) state._deleted = True # can't call state._detach() here, because this state # is still in the transaction snapshot and needs to be # tracked as part of that if persistent_to_deleted is not None: persistent_to_deleted(self, obj) def add(self, instance, _warn=True): """Place an object in the ``Session``. Its state will be persisted to the database on the next flush operation. Repeated calls to ``add()`` will be ignored. The opposite of ``add()`` is ``expunge()``. """ if _warn and self._warn_on_events: self._flush_warning("Session.add()") try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._save_or_update_state(state) def add_all(self, instances): """Add the given collection of instances to this ``Session``.""" if self._warn_on_events: self._flush_warning("Session.add_all()") for instance in instances: self.add(instance, _warn=False) def _save_or_update_state(self, state): state._orphaned_outside_of_session = False self._save_or_update_impl(state) mapper = _state_mapper(state) for o, m, st_, dct_ in mapper.cascade_iterator( "save-update", state, halt_on=self._contains_state ): self._save_or_update_impl(st_) def delete(self, instance): """Mark an instance as deleted. The database delete operation occurs upon ``flush()``. """ if self._warn_on_events: self._flush_warning("Session.delete()") try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._delete_impl(state, instance, head=True) def _delete_impl(self, state, obj, head): if state.key is None: if head: raise sa_exc.InvalidRequestError( "Instance '%s' is not persisted" % state_str(state) ) else: return to_attach = self._before_attach(state, obj) if state in self._deleted: return self.identity_map.add(state) if to_attach: self._after_attach(state, obj) if head: # grab the cascades before adding the item to the deleted list # so that autoflush does not delete the item # the strong reference to the instance itself is significant here cascade_states = list( state.manager.mapper.cascade_iterator("delete", state) ) self._deleted[state] = obj if head: for o, m, st_, dct_ in cascade_states: self._delete_impl(st_, o, False) def merge(self, instance, load=True): """Copy the state of a given instance into a corresponding instance within this :class:`.Session`. :meth:`.Session.merge` examines the primary key attributes of the source instance, and attempts to reconcile it with an instance of the same primary key in the session. If not found locally, it attempts to load the object from the database based on primary key, and if none can be located, creates a new instance. The state of each attribute on the source instance is then copied to the target instance. The resulting target instance is then returned by the method; the original source instance is left unmodified, and un-associated with the :class:`.Session` if not already. This operation cascades to associated instances if the association is mapped with ``cascade="merge"``. See :ref:`unitofwork_merging` for a detailed discussion of merging. .. versionchanged:: 1.1 - :meth:`.Session.merge` will now reconcile pending objects with overlapping primary keys in the same way as persistent. See :ref:`change_3601` for discussion. :param instance: Instance to be merged. :param load: Boolean, when False, :meth:`.merge` switches into a "high performance" mode which causes it to forego emitting history events as well as all database access. This flag is used for cases such as transferring graphs of objects into a :class:`.Session` from a second level cache, or to transfer just-loaded objects into the :class:`.Session` owned by a worker thread or process without re-querying the database. The ``load=False`` use case adds the caveat that the given object has to be in a "clean" state, that is, has no pending changes to be flushed - even if the incoming object is detached from any :class:`.Session`. This is so that when the merge operation populates local attributes and cascades to related objects and collections, the values can be "stamped" onto the target object as is, without generating any history or attribute events, and without the need to reconcile the incoming data with any existing related objects or collections that might not be loaded. The resulting objects from ``load=False`` are always produced as "clean", so it is only appropriate that the given objects should be "clean" as well, else this suggests a mis-use of the method. .. seealso:: :func:`.make_transient_to_detached` - provides for an alternative means of "merging" a single object into the :class:`.Session` """ if self._warn_on_events: self._flush_warning("Session.merge()") _recursive = {} _resolve_conflict_map = {} if load: # flush current contents if we expect to load data self._autoflush() object_mapper(instance) # verify mapped autoflush = self.autoflush try: self.autoflush = False return self._merge( attributes.instance_state(instance), attributes.instance_dict(instance), load=load, _recursive=_recursive, _resolve_conflict_map=_resolve_conflict_map, ) finally: self.autoflush = autoflush def _merge( self, state, state_dict, load=True, _recursive=None, _resolve_conflict_map=None, ): mapper = _state_mapper(state) if state in _recursive: return _recursive[state] new_instance = False key = state.key if key is None: if state in self._new: util.warn( "Instance %s is already pending in this Session yet is " "being merged again; this is probably not what you want " "to do" % state_str(state) ) if not load: raise sa_exc.InvalidRequestError( "merge() with load=False option does not support " "objects transient (i.e. unpersisted) objects. flush() " "all changes on mapped instances before merging with " "load=False." ) key = mapper._identity_key_from_state(state) key_is_persistent = attributes.NEVER_SET not in key[1] and ( not _none_set.intersection(key[1]) or ( mapper.allow_partial_pks and not _none_set.issuperset(key[1]) ) ) else: key_is_persistent = True if key in self.identity_map: try: merged = self.identity_map[key] except KeyError: # object was GC'ed right as we checked for it merged = None else: merged = None if merged is None: if key_is_persistent and key in _resolve_conflict_map: merged = _resolve_conflict_map[key] elif not load: if state.modified: raise sa_exc.InvalidRequestError( "merge() with load=False option does not support " "objects marked as 'dirty'. flush() all changes on " "mapped instances before merging with load=False." ) merged = mapper.class_manager.new_instance() merged_state = attributes.instance_state(merged) merged_state.key = key self._update_impl(merged_state) new_instance = True elif key_is_persistent: merged = self.query(mapper.class_).get(key[1]) if merged is None: merged = mapper.class_manager.new_instance() merged_state = attributes.instance_state(merged) merged_dict = attributes.instance_dict(merged) new_instance = True self._save_or_update_state(merged_state) else: merged_state = attributes.instance_state(merged) merged_dict = attributes.instance_dict(merged) _recursive[state] = merged _resolve_conflict_map[key] = merged # check that we didn't just pull the exact same # state out. if state is not merged_state: # version check if applicable if mapper.version_id_col is not None: existing_version = mapper._get_state_attr_by_column( state, state_dict, mapper.version_id_col, passive=attributes.PASSIVE_NO_INITIALIZE, ) merged_version = mapper._get_state_attr_by_column( merged_state, merged_dict, mapper.version_id_col, passive=attributes.PASSIVE_NO_INITIALIZE, ) if ( existing_version is not attributes.PASSIVE_NO_RESULT and merged_version is not attributes.PASSIVE_NO_RESULT and existing_version != merged_version ): raise exc.StaleDataError( "Version id '%s' on merged state %s " "does not match existing version '%s'. " "Leave the version attribute unset when " "merging to update the most recent version." % ( existing_version, state_str(merged_state), merged_version, ) ) merged_state.load_path = state.load_path merged_state.load_options = state.load_options # since we are copying load_options, we need to copy # the callables_ that would have been generated by those # load_options. # assumes that the callables we put in state.callables_ # are not instance-specific (which they should not be) merged_state._copy_callables(state) for prop in mapper.iterate_properties: prop.merge( self, state, state_dict, merged_state, merged_dict, load, _recursive, _resolve_conflict_map, ) if not load: # remove any history merged_state._commit_all(merged_dict, self.identity_map) if new_instance: merged_state.manager.dispatch.load(merged_state, None) return merged def _validate_persistent(self, state): if not self.identity_map.contains_state(state): raise sa_exc.InvalidRequestError( "Instance '%s' is not persistent within this Session" % state_str(state) ) def _save_impl(self, state): if state.key is not None: raise sa_exc.InvalidRequestError( "Object '%s' already has an identity - " "it can't be registered as pending" % state_str(state) ) obj = state.obj() to_attach = self._before_attach(state, obj) if state not in self._new: self._new[state] = obj state.insert_order = len(self._new) if to_attach: self._after_attach(state, obj) def _update_impl(self, state, revert_deletion=False): if state.key is None: raise sa_exc.InvalidRequestError( "Instance '%s' is not persisted" % state_str(state) ) if state._deleted: if revert_deletion: if not state._attached: return del state._deleted else: raise sa_exc.InvalidRequestError( "Instance '%s' has been deleted. " "Use the make_transient() " "function to send this object back " "to the transient state." % state_str(state) ) obj = state.obj() # check for late gc if obj is None: return to_attach = self._before_attach(state, obj) self._deleted.pop(state, None) if revert_deletion: self.identity_map.replace(state) else: self.identity_map.add(state) if to_attach: self._after_attach(state, obj) elif revert_deletion: self.dispatch.deleted_to_persistent(self, obj) def _save_or_update_impl(self, state): if state.key is None: self._save_impl(state) else: self._update_impl(state) def enable_relationship_loading(self, obj): """Associate an object with this :class:`.Session` for related object loading. .. warning:: :meth:`.enable_relationship_loading` exists to serve special use cases and is not recommended for general use. Accesses of attributes mapped with :func:`.relationship` will attempt to load a value from the database using this :class:`.Session` as the source of connectivity. The values will be loaded based on foreign key and primary key values present on this object - if not present, then those relationships will be unavailable. The object will be attached to this session, but will **not** participate in any persistence operations; its state for almost all purposes will remain either "transient" or "detached", except for the case of relationship loading. Also note that backrefs will often not work as expected. Altering a relationship-bound attribute on the target object may not fire off a backref event, if the effective value is what was already loaded from a foreign-key-holding value. The :meth:`.Session.enable_relationship_loading` method is similar to the ``load_on_pending`` flag on :func:`.relationship`. Unlike that flag, :meth:`.Session.enable_relationship_loading` allows an object to remain transient while still being able to load related items. To make a transient object associated with a :class:`.Session` via :meth:`.Session.enable_relationship_loading` pending, add it to the :class:`.Session` using :meth:`.Session.add` normally. If the object instead represents an existing identity in the database, it should be merged using :meth:`.Session.merge`. :meth:`.Session.enable_relationship_loading` does not improve behavior when the ORM is used normally - object references should be constructed at the object level, not at the foreign key level, so that they are present in an ordinary way before flush() proceeds. This method is not intended for general use. .. seealso:: ``load_on_pending`` at :func:`.relationship` - this flag allows per-relationship loading of many-to-ones on items that are pending. :func:`.make_transient_to_detached` - allows for an object to be added to a :class:`.Session` without SQL emitted, which then will unexpire attributes on access. """ state = attributes.instance_state(obj) to_attach = self._before_attach(state, obj) state._load_pending = True if to_attach: self._after_attach(state, obj) def _before_attach(self, state, obj): if state.session_id == self.hash_key: return False if state.session_id and state.session_id in _sessions: raise sa_exc.InvalidRequestError( "Object '%s' is already attached to session '%s' " "(this is '%s')" % (state_str(state), state.session_id, self.hash_key) ) self.dispatch.before_attach(self, obj) return True def _after_attach(self, state, obj): state.session_id = self.hash_key if state.modified and state._strong_obj is None: state._strong_obj = obj self.dispatch.after_attach(self, obj) if state.key: self.dispatch.detached_to_persistent(self, obj) else: self.dispatch.transient_to_pending(self, obj) def __contains__(self, instance): """Return True if the instance is associated with this session. The instance may be pending or persistent within the Session for a result of True. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) return self._contains_state(state) def __iter__(self): """Iterate over all pending or persistent instances within this Session. """ return iter( list(self._new.values()) + list(self.identity_map.values()) ) def _contains_state(self, state): return state in self._new or self.identity_map.contains_state(state) def flush(self, objects=None): """Flush all the object changes to the database. Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session's unit of work dependency solver. Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database's transaction buffer. For ``autocommit`` Sessions with no active manual transaction, flush() will create a transaction on the fly that surrounds the entire set of operations into the flush. :param objects: Optional; restricts the flush operation to operate only on elements that are in the given collection. This feature is for an extremely narrow set of use cases where particular objects may need to be operated upon before the full flush() occurs. It is not intended for general use. """ if self._flushing: raise sa_exc.InvalidRequestError("Session is already flushing") if self._is_clean(): return try: self._flushing = True self._flush(objects) finally: self._flushing = False def _flush_warning(self, method): util.warn( "Usage of the '%s' operation is not currently supported " "within the execution stage of the flush process. " "Results may not be consistent. Consider using alternative " "event listeners or connection-level operations instead." % method ) def _is_clean(self): return ( not self.identity_map.check_modified() and not self._deleted and not self._new ) def _flush(self, objects=None): dirty = self._dirty_states if not dirty and not self._deleted and not self._new: self.identity_map._modified.clear() return flush_context = UOWTransaction(self) if self.dispatch.before_flush: self.dispatch.before_flush(self, flush_context, objects) # re-establish "dirty states" in case the listeners # added dirty = self._dirty_states deleted = set(self._deleted) new = set(self._new) dirty = set(dirty).difference(deleted) # create the set of all objects we want to operate upon if objects: # specific list passed in objset = set() for o in objects: try: state = attributes.instance_state(o) except exc.NO_STATE: raise exc.UnmappedInstanceError(o) objset.add(state) else: objset = None # store objects whose fate has been decided processed = set() # put all saves/updates into the flush context. detect top-level # orphans and throw them into deleted. if objset: proc = new.union(dirty).intersection(objset).difference(deleted) else: proc = new.union(dirty).difference(deleted) for state in proc: is_orphan = _state_mapper(state)._is_orphan(state) is_persistent_orphan = is_orphan and state.has_identity if ( is_orphan and not is_persistent_orphan and state._orphaned_outside_of_session ): self._expunge_states([state]) else: _reg = flush_context.register_object( state, isdelete=is_persistent_orphan ) assert _reg, "Failed to add object to the flush context!" processed.add(state) # put all remaining deletes into the flush context. if objset: proc = deleted.intersection(objset).difference(processed) else: proc = deleted.difference(processed) for state in proc: _reg = flush_context.register_object(state, isdelete=True) assert _reg, "Failed to add object to the flush context!" if not flush_context.has_work: return flush_context.transaction = transaction = self.begin( subtransactions=True ) try: self._warn_on_events = True try: flush_context.execute() finally: self._warn_on_events = False self.dispatch.after_flush(self, flush_context) flush_context.finalize_flush_changes() if not objects and self.identity_map._modified: len_ = len(self.identity_map._modified) statelib.InstanceState._commit_all_states( [ (state, state.dict) for state in self.identity_map._modified ], instance_dict=self.identity_map, ) util.warn( "Attribute history events accumulated on %d " "previously clean instances " "within inner-flush event handlers have been " "reset, and will not result in database updates. " "Consider using set_committed_value() within " "inner-flush event handlers to avoid this warning." % len_ ) # useful assertions: # if not objects: # assert not self.identity_map._modified # else: # assert self.identity_map._modified == \ # self.identity_map._modified.difference(objects) self.dispatch.after_flush_postexec(self, flush_context) transaction.commit() except: with util.safe_reraise(): transaction.rollback(_capture_exception=True) def bulk_save_objects( self, objects, return_defaults=False, update_changed_only=True, preserve_order=True, ): """Perform a bulk save of the given list of objects. The bulk save feature allows mapped objects to be used as the source of simple INSERT and UPDATE operations which can be more easily grouped together into higher performing "executemany" operations; the extraction of data from the objects is also performed using a lower-latency process that ignores whether or not attributes have actually been modified in the case of UPDATEs, and also ignores SQL expressions. The objects as given are not added to the session and no additional state is established on them, unless the ``return_defaults`` flag is also set, in which case primary key attributes and server-side default values will be populated. .. versionadded:: 1.0.0 .. warning:: The bulk save feature allows for a lower-latency INSERT/UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are **silently omitted** in favor of raw INSERT/UPDATES of records. **Please read the list of caveats at** :ref:`bulk_operations` **before using this method, and fully test and confirm the functionality of all code developed using these systems.** :param objects: a list of mapped object instances. The mapped objects are persisted as is, and are **not** associated with the :class:`.Session` afterwards. For each object, whether the object is sent as an INSERT or an UPDATE is dependent on the same rules used by the :class:`.Session` in traditional operation; if the object has the :attr:`.InstanceState.key` attribute set, then the object is assumed to be "detached" and will result in an UPDATE. Otherwise, an INSERT is used. In the case of an UPDATE, statements are grouped based on which attributes have changed, and are thus to be the subject of each SET clause. If ``update_changed_only`` is False, then all attributes present within each object are applied to the UPDATE statement, which may help in allowing the statements to be grouped together into a larger executemany(), and will also reduce the overhead of checking history on attributes. :param return_defaults: when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted **one at a time**, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, :paramref:`.Session.bulk_save_objects.return_defaults` **greatly reduces the performance gains** of the method overall. :param update_changed_only: when True, UPDATE statements are rendered based on those attributes in each state that have logged changes. When False, all attributes present are rendered into the SET clause with the exception of primary key attributes. :param preserve_order: when True, the order of inserts and updates matches exactly the order in which the objects are given. When False, common types of objects are grouped into inserts and updates, to allow for more batching opportunities. .. versionadded:: 1.3 .. seealso:: :ref:`bulk_operations` :meth:`.Session.bulk_insert_mappings` :meth:`.Session.bulk_update_mappings` """ def key(state): return (state.mapper, state.key is not None) obj_states = tuple(attributes.instance_state(obj) for obj in objects) if not preserve_order: obj_states = sorted(obj_states, key=key) for (mapper, isupdate), states in itertools.groupby(obj_states, key): self._bulk_save_mappings( mapper, states, isupdate, True, return_defaults, update_changed_only, False, ) def bulk_insert_mappings( self, mapper, mappings, return_defaults=False, render_nulls=False ): """Perform a bulk insert of the given list of mapping dictionaries. The bulk insert feature allows plain Python dictionaries to be used as the source of simple INSERT operations which can be more easily grouped together into higher performing "executemany" operations. Using dictionaries, there is no "history" or session state management features in use, reducing latency when inserting large numbers of simple rows. The values within the dictionaries as given are typically passed without modification into Core :meth:`.Insert` constructs, after organizing the values within them across the tables to which the given mapper is mapped. .. versionadded:: 1.0.0 .. warning:: The bulk insert feature allows for a lower-latency INSERT of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are **silently omitted** in favor of raw INSERT of records. **Please read the list of caveats at** :ref:`bulk_operations` **before using this method, and fully test and confirm the functionality of all code developed using these systems.** :param mapper: a mapped class, or the actual :class:`.Mapper` object, representing the single kind of object represented within the mapping list. :param mappings: a list of dictionaries, each one containing the state of the mapped row to be inserted, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary must contain all keys to be populated into all tables. :param return_defaults: when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted **one at a time**, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, :paramref:`.Session.bulk_insert_mappings.return_defaults` **greatly reduces the performance gains** of the method overall. If the rows to be inserted only refer to a single table, then there is no reason this flag should be set as the returned default information is not used. :param render_nulls: When True, a value of ``None`` will result in a NULL value being included in the INSERT statement, rather than the column being omitted from the INSERT. This allows all the rows being INSERTed to have the identical set of columns which allows the full set of rows to be batched to the DBAPI. Normally, each column-set that contains a different combination of NULL values than the previous row must omit a different series of columns from the rendered INSERT statement, which means it must be emitted as a separate statement. By passing this flag, the full set of rows are guaranteed to be batchable into one batch; the cost however is that server-side defaults which are invoked by an omitted column will be skipped, so care must be taken to ensure that these are not necessary. .. warning:: When this flag is set, **server side default SQL values will not be invoked** for those columns that are inserted as NULL; the NULL value will be sent explicitly. Care must be taken to ensure that no server-side default functions need to be invoked for the operation as a whole. .. versionadded:: 1.1 .. seealso:: :ref:`bulk_operations` :meth:`.Session.bulk_save_objects` :meth:`.Session.bulk_update_mappings` """ self._bulk_save_mappings( mapper, mappings, False, False, return_defaults, False, render_nulls, ) def bulk_update_mappings(self, mapper, mappings): """Perform a bulk update of the given list of mapping dictionaries. The bulk update feature allows plain Python dictionaries to be used as the source of simple UPDATE operations which can be more easily grouped together into higher performing "executemany" operations. Using dictionaries, there is no "history" or session state management features in use, reducing latency when updating large numbers of simple rows. .. versionadded:: 1.0.0 .. warning:: The bulk update feature allows for a lower-latency UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are **silently omitted** in favor of raw UPDATES of records. **Please read the list of caveats at** :ref:`bulk_operations` **before using this method, and fully test and confirm the functionality of all code developed using these systems.** :param mapper: a mapped class, or the actual :class:`.Mapper` object, representing the single kind of object represented within the mapping list. :param mappings: a list of dictionaries, each one containing the state of the mapped row to be updated, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary may contain keys corresponding to all tables. All those keys which are present and are not part of the primary key are applied to the SET clause of the UPDATE statement; the primary key values, which are required, are applied to the WHERE clause. .. seealso:: :ref:`bulk_operations` :meth:`.Session.bulk_insert_mappings` :meth:`.Session.bulk_save_objects` """ self._bulk_save_mappings( mapper, mappings, True, False, False, False, False ) def _bulk_save_mappings( self, mapper, mappings, isupdate, isstates, return_defaults, update_changed_only, render_nulls, ): mapper = _class_to_mapper(mapper) self._flushing = True transaction = self.begin(subtransactions=True) try: if isupdate: persistence._bulk_update( mapper, mappings, transaction, isstates, update_changed_only, ) else: persistence._bulk_insert( mapper, mappings, transaction, isstates, return_defaults, render_nulls, ) transaction.commit() except: with util.safe_reraise(): transaction.rollback(_capture_exception=True) finally: self._flushing = False @util.deprecated_params( passive=( "0.8", "The :paramref:`.Session.is_modified.passive` flag is deprecated " "and will be removed in a future release. The flag is no longer " "used and is ignored.", ) ) def is_modified(self, instance, include_collections=True, passive=None): r"""Return ``True`` if the given instance has locally modified attributes. This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously committed value, if any. It is in effect a more expensive and accurate version of checking for the given instance in the :attr:`.Session.dirty` collection; a full test for each attribute's net "dirty" status is performed. E.g.:: return session.is_modified(someobject) A few caveats to this method apply: * Instances present in the :attr:`.Session.dirty` collection may report ``False`` when tested with this method. This is because the object may have received change events via attribute mutation, thus placing it in :attr:`.Session.dirty`, but ultimately the state is the same as that loaded from the database, resulting in no net change here. * Scalar attributes may not have recorded the previously set value when a new value was applied, if the attribute was not loaded, or was expired, at the time the new value was received - in these cases, the attribute is assumed to have a change, even if there is ultimately no net change against its database value. SQLAlchemy in most cases does not need the "old" value when a set event occurs, so it skips the expense of a SQL call if the old value isn't present, based on the assumption that an UPDATE of the scalar value is usually needed, and in those few cases where it isn't, is less expensive on average than issuing a defensive SELECT. The "old" value is fetched unconditionally upon set only if the attribute container has the ``active_history`` flag set to ``True``. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the ``active_history`` argument with :func:`.column_property`. :param instance: mapped instance to be tested for pending changes. :param include_collections: Indicates if multivalued collections should be included in the operation. Setting this to ``False`` is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush. :param passive: not used """ state = object_state(instance) if not state.modified: return False dict_ = state.dict for attr in state.manager.attributes: if ( not include_collections and hasattr(attr.impl, "get_collection") ) or not hasattr(attr.impl, "get_history"): continue (added, unchanged, deleted) = attr.impl.get_history( state, dict_, passive=attributes.NO_CHANGE ) if added or deleted: return True else: return False @property def is_active(self): """True if this :class:`.Session` is in "transaction mode" and is not in "partial rollback" state. The :class:`.Session` in its default mode of ``autocommit=False`` is essentially always in "transaction mode", in that a :class:`.SessionTransaction` is associated with it as soon as it is instantiated. This :class:`.SessionTransaction` is immediately replaced with a new one as soon as it is ended, due to a rollback, commit, or close operation. "Transaction mode" does *not* indicate whether or not actual database connection resources are in use; the :class:`.SessionTransaction` object coordinates among zero or more actual database transactions, and starts out with none, accumulating individual DBAPI connections as different data sources are used within its scope. The best way to track when a particular :class:`.Session` has actually begun to use DBAPI resources is to implement a listener using the :meth:`.SessionEvents.after_begin` method, which will deliver both the :class:`.Session` as well as the target :class:`.Connection` to a user-defined event listener. The "partial rollback" state refers to when an "inner" transaction, typically used during a flush, encounters an error and emits a rollback of the DBAPI connection. At this point, the :class:`.Session` is in "partial rollback" and awaits for the user to call :meth:`.Session.rollback`, in order to close out the transaction stack. It is in this "partial rollback" period that the :attr:`.is_active` flag returns False. After the call to :meth:`.Session.rollback`, the :class:`.SessionTransaction` is replaced with a new one and :attr:`.is_active` returns ``True`` again. When a :class:`.Session` is used in ``autocommit=True`` mode, the :class:`.SessionTransaction` is only instantiated within the scope of a flush call, or when :meth:`.Session.begin` is called. So :attr:`.is_active` will always be ``False`` outside of a flush or :meth:`.Session.begin` block in this mode, and will be ``True`` within the :meth:`.Session.begin` block as long as it doesn't enter "partial rollback" state. From all the above, it follows that the only purpose to this flag is for application frameworks that wish to detect is a "rollback" is necessary within a generic error handling routine, for :class:`.Session` objects that would otherwise be in "partial rollback" mode. In a typical integration case, this is also not necessary as it is standard practice to emit :meth:`.Session.rollback` unconditionally within the outermost exception catch. To track the transactional state of a :class:`.Session` fully, use event listeners, primarily the :meth:`.SessionEvents.after_begin`, :meth:`.SessionEvents.after_commit`, :meth:`.SessionEvents.after_rollback` and related events. """ return self.transaction and self.transaction.is_active identity_map = None """A mapping of object identities to objects themselves. Iterating through ``Session.identity_map.values()`` provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session. .. seealso:: :func:`.identity_key` - helper function to produce the keys used in this dictionary. """ @property def _dirty_states(self): """The set of all persistent states considered dirty. This method returns all states that were modified including those that were possibly deleted. """ return self.identity_map._dirty_states() @property def dirty(self): """The set of all persistent instances considered dirty. E.g.:: some_mapped_object in session.dirty Instances are considered dirty when they were modified but not deleted. Note that this 'dirty' calculation is 'optimistic'; most attribute-setting or collection modification operations will mark an instance as 'dirty' and place it in this set, even if there is no net change to the attribute's value. At flush time, the value of each attribute is compared to its previously saved value, and if there's no net change, no SQL operation will occur (this is a more expensive operation so it's only done at flush time). To check if an instance has actionable net changes to its attributes, use the :meth:`.Session.is_modified` method. """ return util.IdentitySet( [ state.obj() for state in self._dirty_states if state not in self._deleted ] ) @property def deleted(self): "The set of all instances marked as 'deleted' within this ``Session``" return util.IdentitySet(list(self._deleted.values())) @property def new(self): "The set of all instances marked as 'new' within this ``Session``." return util.IdentitySet(list(self._new.values())) class sessionmaker(_SessionClassMethods): """A configurable :class:`.Session` factory. The :class:`.sessionmaker` factory generates new :class:`.Session` objects when called, creating them given the configurational arguments established here. e.g.:: # global scope Session = sessionmaker(autoflush=False) # later, in a local scope, create and use a session: sess = Session() Any keyword arguments sent to the constructor itself will override the "configured" keywords:: Session = sessionmaker() # bind an individual session to a connection sess = Session(bind=connection) The class also includes a method :meth:`.configure`, which can be used to specify additional keyword arguments to the factory, which will take effect for subsequent :class:`.Session` objects generated. This is usually used to associate one or more :class:`.Engine` objects with an existing :class:`.sessionmaker` factory before it is first used:: # application starts Session = sessionmaker() # ... later engine = create_engine('sqlite:///foo.db') Session.configure(bind=engine) sess = Session() .. seealso: :ref:`session_getting` - introductory text on creating sessions using :class:`.sessionmaker`. """ def __init__( self, bind=None, class_=Session, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw ): r"""Construct a new :class:`.sessionmaker`. All arguments here except for ``class_`` correspond to arguments accepted by :class:`.Session` directly. See the :meth:`.Session.__init__` docstring for more details on parameters. :param bind: a :class:`.Engine` or other :class:`.Connectable` with which newly created :class:`.Session` objects will be associated. :param class\_: class to use in order to create new :class:`.Session` objects. Defaults to :class:`.Session`. :param autoflush: The autoflush setting to use with newly created :class:`.Session` objects. :param autocommit: The autocommit setting to use with newly created :class:`.Session` objects. :param expire_on_commit=True: the expire_on_commit setting to use with newly created :class:`.Session` objects. :param info: optional dictionary of information that will be available via :attr:`.Session.info`. Note this dictionary is *updated*, not replaced, when the ``info`` parameter is specified to the specific :class:`.Session` construction operation. .. versionadded:: 0.9.0 :param \**kw: all other keyword arguments are passed to the constructor of newly created :class:`.Session` objects. """ kw["bind"] = bind kw["autoflush"] = autoflush kw["autocommit"] = autocommit kw["expire_on_commit"] = expire_on_commit if info is not None: kw["info"] = info self.kw = kw # make our own subclass of the given class, so that # events can be associated with it specifically. self.class_ = type(class_.__name__, (class_,), {}) def __call__(self, **local_kw): """Produce a new :class:`.Session` object using the configuration established in this :class:`.sessionmaker`. In Python, the ``__call__`` method is invoked on an object when it is "called" in the same way as a function:: Session = sessionmaker() session = Session() # invokes sessionmaker.__call__() """ for k, v in self.kw.items(): if k == "info" and "info" in local_kw: d = v.copy() d.update(local_kw["info"]) local_kw["info"] = d else: local_kw.setdefault(k, v) return self.class_(**local_kw) def configure(self, **new_kw): """(Re)configure the arguments for this sessionmaker. e.g.:: Session = sessionmaker() Session.configure(bind=create_engine('sqlite://')) """ self.kw.update(new_kw) def __repr__(self): return "%s(class_=%r, %s)" % ( self.__class__.__name__, self.class_.__name__, ", ".join("%s=%r" % (k, v) for k, v in self.kw.items()), ) def close_all_sessions(): """Close all sessions in memory. This function consults a global registry of all :class:`.Session` objects and calls :meth:`.Session.close` on them, which resets them to a clean state. This function is not for general use but may be useful for test suites within the teardown scheme. .. versionadded:: 1.3 """ for sess in _sessions.values(): sess.close() def make_transient(instance): """Alter the state of the given instance so that it is :term:`transient`. .. note:: :func:`.make_transient` is a special-case function for advanced use cases only. The given mapped instance is assumed to be in the :term:`persistent` or :term:`detached` state. The function will remove its association with any :class:`.Session` as well as its :attr:`.InstanceState.identity`. The effect is that the object will behave as though it were newly constructed, except retaining any attribute / collection values that were loaded at the time of the call. The :attr:`.InstanceState.deleted` flag is also reset if this object had been deleted as a result of using :meth:`.Session.delete`. .. warning:: :func:`.make_transient` does **not** "unexpire" or otherwise eagerly load ORM-mapped attributes that are not currently loaded at the time the function is called. This includes attributes which: * were expired via :meth:`.Session.expire` * were expired as the natural effect of committing a session transaction, e.g. :meth:`.Session.commit` * are normally :term:`lazy loaded` but are not currently loaded * are "deferred" via :ref:`deferred` and are not yet loaded * were not present in the query which loaded this object, such as that which is common in joined table inheritance and other scenarios. After :func:`.make_transient` is called, unloaded attributes such as those above will normally resolve to the value ``None`` when accessed, or an empty collection for a collection-oriented attribute. As the object is transient and un-associated with any database identity, it will no longer retrieve these values. .. seealso:: :func:`.make_transient_to_detached` """ state = attributes.instance_state(instance) s = _state_session(state) if s: s._expunge_states([state]) # remove expired state state.expired_attributes.clear() # remove deferred callables if state.callables: del state.callables if state.key: del state.key if state._deleted: del state._deleted def make_transient_to_detached(instance): """Make the given transient instance :term:`detached`. .. note:: :func:`.make_transient_to_detached` is a special-case function for advanced use cases only. All attribute history on the given instance will be reset as though the instance were freshly loaded from a query. Missing attributes will be marked as expired. The primary key attributes of the object, which are required, will be made into the "key" of the instance. The object can then be added to a session, or merged possibly with the load=False flag, at which point it will look as if it were loaded that way, without emitting SQL. This is a special use case function that differs from a normal call to :meth:`.Session.merge` in that a given persistent state can be manufactured without any SQL calls. .. versionadded:: 0.9.5 .. seealso:: :func:`.make_transient` :meth:`.Session.enable_relationship_loading` """ state = attributes.instance_state(instance) if state.session_id or state.key: raise sa_exc.InvalidRequestError("Given object must be transient") state.key = state.mapper._identity_key_from_state(state) if state._deleted: del state._deleted state._commit_all(state.dict) state._expire_attributes(state.dict, state.unloaded_expirable) def object_session(instance): """Return the :class:`.Session` to which the given instance belongs. This is essentially the same as the :attr:`.InstanceState.session` accessor. See that attribute for details. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) else: return _state_session(state) _new_sessionid = util.counter()