sqlalchemy.orm.session.Session

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.

Undocumented

Undocumented

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 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. .. seealso:: :ref:`session_flushing` - additional background on autoflush :param autobegin: Automatically start transactions (i.e. equivalent to invoking :meth:`_orm.Session.begin`) when database access is requested by an operation. Defaults to ``True``. Set to ``False`` to prevent a :class:`_orm.Session` from implicitly beginning transactions after construction, as well as after any of the :meth:`_orm.Session.rollback`, :meth:`_orm.Session.commit`, or :meth:`_orm.Session.close` methods are called. .. versionadded:: 2.0 .. seealso:: :ref:`session_autobegin_disable` :param bind: An optional :class:`_engine.Engine` or :class:`_engine.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.Engine` or :class:`_engine.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:`_schema.Table` objects and :class:`_orm.Mapper` objects. The values of the dictionary are then instances of :class:`_engine.Engine` or less commonly :class:`_engine.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.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+psycopg2://engine1'), SomeDeclarativeBase: create_engine('postgresql+psycopg2://engine2'), some_mapper: create_engine('postgresql+psycopg2://engine3'), some_table: create_engine('postgresql+psycopg2://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: legacy; defaults to ``True``. A parameter 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``, caching as used by this particular extension is disabled. .. versionchanged:: 1.4 The ``sqlalchemy.ext.baked`` extension is legacy and is not used by any of SQLAlchemy's internals. This flag therefore only affects applications that are making explicit use of this extension within their own code. :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. .. seealso:: :ref:`session_committing` :param future: Deprecated; this flag is always True. .. seealso:: :ref:`migration_20_toplevel` :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`. :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.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 autocommit: the "autocommit" keyword is present for backwards compatibility but must remain at its default value of ``False``. :param join_transaction_mode: Describes the transactional behavior to take when a given bind is a :class:`_engine.Connection` that has already begun a transaction outside the scope of this :class:`_orm.Session`; in other words the :meth:`_engine.Connection.in_transaction()` method returns True. The following behaviors only take effect when the :class:`_orm.Session` **actually makes use of the connection given**; that is, a method such as :meth:`_orm.Session.execute`, :meth:`_orm.Session.connection`, etc. are actually invoked: * ``"conditional_savepoint"`` - this is the default. if the given :class:`_engine.Connection` is begun within a transaction but does not have a SAVEPOINT, then ``"rollback_only"`` is used. If the :class:`_engine.Connection` is additionally within a SAVEPOINT, in other words :meth:`_engine.Connection.in_nested_transaction()` method returns True, then ``"create_savepoint"`` is used. ``"conditional_savepoint"`` behavior attempts to make use of savepoints in order to keep the state of the existing transaction unchanged, but only if there is already a savepoint in progress; otherwise, it is not assumed that the backend in use has adequate support for SAVEPOINT, as availability of this feature varies. ``"conditional_savepoint"`` also seeks to establish approximate backwards compatibility with previous :class:`_orm.Session` behavior, for applications that are not setting a specific mode. It is recommended that one of the explicit settings be used. * ``"create_savepoint"`` - the :class:`_orm.Session` will use :meth:`_engine.Connection.begin_nested()` in all cases to create its own transaction. This transaction by its nature rides "on top" of any existing transaction that's opened on the given :class:`_engine.Connection`; if the underlying database and the driver in use has full, non-broken support for SAVEPOINT, the external transaction will remain unaffected throughout the lifespan of the :class:`_orm.Session`. The ``"create_savepoint"`` mode is the most useful for integrating a :class:`_orm.Session` into a test suite where an externally initiated transaction should remain unaffected; however, it relies on proper SAVEPOINT support from the underlying driver and database. .. tip:: When using SQLite, the SQLite driver included through Python 3.11 does not handle SAVEPOINTs correctly in all cases without workarounds. See the section :ref:`pysqlite_serializable` for details on current workarounds. * ``"control_fully"`` - the :class:`_orm.Session` will take control of the given transaction as its own; :meth:`_orm.Session.commit` will call ``.commit()`` on the transaction, :meth:`_orm.Session.rollback` will call ``.rollback()`` on the transaction, :meth:`_orm.Session.close` will call ``.rollback`` on the transaction. .. tip:: This mode of use is equivalent to how SQLAlchemy 1.4 would handle a :class:`_engine.Connection` given with an existing SAVEPOINT (i.e. :meth:`_engine.Connection.begin_nested`); the :class:`_orm.Session` would take full control of the existing SAVEPOINT. * ``"rollback_only"`` - the :class:`_orm.Session` will take control of the given transaction for ``.rollback()`` calls only; ``.commit()`` calls will not be propagated to the given transaction. ``.close()`` calls will have no effect on the given transaction. .. tip:: This mode of use is equivalent to how SQLAlchemy 1.4 would handle a :class:`_engine.Connection` given with an existing regular database transaction (i.e. :meth:`_engine.Connection.begin`); the :class:`_orm.Session` would propagate :meth:`_orm.Session.rollback` calls to the underlying transaction, but not :meth:`_orm.Session.commit` or :meth:`_orm.Session.close` calls. .. versionadded:: 2.0.0rc1

Iterate over all pending or persistent instances within this Session.

Place an object into this :class:`_orm.Session`. Objects that are in the :term:`transient` state when passed to the :meth:`_orm.Session.add` method will move to the :term:`pending` state, until the next flush, at which point they will move to the :term:`persistent` state. Objects that are in the :term:`detached` state when passed to the :meth:`_orm.Session.add` method will move to the :term:`persistent` state directly. If the transaction used by the :class:`_orm.Session` is rolled back, objects which were transient when they were passed to :meth:`_orm.Session.add` will be moved back to the :term:`transient` state, and will no longer be present within this :class:`_orm.Session`. .. seealso:: :meth:`_orm.Session.add_all` :ref:`session_adding` - at :ref:`session_basics`

Add the given collection of instances to this :class:`_orm.Session`. See the documentation for :meth:`_orm.Session.add` for a general behavioral description. .. seealso:: :meth:`_orm.Session.add` :ref:`session_adding` - at :ref:`session_basics`

Begin a transaction, or nested transaction, on this :class:`.Session`, if one is not already begun. The :class:`_orm.Session` object features **autobegin** behavior, so that normally it is not necessary to call the :meth:`_orm.Session.begin` method explicitly. However, it may be used in order to control the scope of when the transactional state is begun. When used to begin the outermost transaction, an error is raised if this :class:`.Session` is already inside of a transaction. :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_explicit_begin` for an example. .. seealso:: :ref:`session_autobegin` :ref:`unitofwork_transaction` :meth:`.Session.begin_nested`

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.

Associate a :class:`_orm.Mapper` or arbitrary Python class with a "bind", e.g. an :class:`_engine.Engine` or :class:`_engine.Connection`. The given entity is added to a lookup used by the :meth:`.Session.get_bind` method. :param mapper: a :class:`_orm.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.Engine` or :class:`_engine.Connection` object. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_table`

Associate a :class:`_schema.Table` with a "bind", e.g. an :class:`_engine.Engine` or :class:`_engine.Connection`. The given :class:`_schema.Table` is added to a lookup used by the :meth:`.Session.get_bind` method. :param table: a :class:`_schema.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.Engine` or :class:`_engine.Connection` object. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_mapper`

Perform a bulk insert of the given list of mapping dictionaries. .. legacy:: This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections :ref:`orm_queryguide_bulk_insert` and :ref:`orm_queryguide_bulk_update`. The 2.0 API shares implementation details with this method and adds new features as well. :param mapper: a mapped class, or the actual :class:`_orm.Mapper` object, representing the single kind of object represented within the mapping list. :param mappings: a sequence 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, the INSERT process will be altered to ensure that newly generated primary key values will be fetched. The rationale for this parameter is typically to enable :ref:`Joined Table Inheritance <joined_inheritance>` mappings to be bulk inserted. .. note:: for backends that don't support RETURNING, the :paramref:`_orm.Session.bulk_insert_mappings.return_defaults` parameter can significantly decrease performance as INSERT statements can no longer be batched. See :ref:`engine_insertmanyvalues` for background on which backends are affected. :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. .. seealso:: :doc:`queryguide/dml` :meth:`.Session.bulk_save_objects` :meth:`.Session.bulk_update_mappings`

Perform a bulk save of the given list of objects. .. legacy:: This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections :ref:`orm_queryguide_bulk_insert` and :ref:`orm_queryguide_bulk_update`. For general INSERT and UPDATE of existing ORM mapped objects, prefer standard :term:`unit of work` data management patterns, introduced in the :ref:`unified_tutorial` at :ref:`tutorial_orm_data_manipulation`. SQLAlchemy 2.0 now uses :ref:`engine_insertmanyvalues` with modern dialects which solves previous issues of bulk INSERT slowness. :param objects: a sequence 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. It is strongly advised to please use the standard :meth:`_orm.Session.add_all` approach. :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. .. seealso:: :doc:`queryguide/dml` :meth:`.Session.bulk_insert_mappings` :meth:`.Session.bulk_update_mappings`

Perform a bulk update of the given list of mapping dictionaries. .. legacy:: This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections :ref:`orm_queryguide_bulk_insert` and :ref:`orm_queryguide_bulk_update`. The 2.0 API shares implementation details with this method and adds new features as well. :param mapper: a mapped class, or the actual :class:`_orm.Mapper` object, representing the single kind of object represented within the mapping list. :param mappings: a sequence 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:: :doc:`queryguide/dml` :meth:`.Session.bulk_insert_mappings` :meth:`.Session.bulk_save_objects`

Close out the transactional resources and ORM objects used by this :class:`_orm.Session`. This expunges all ORM objects associated with this :class:`_orm.Session`, ends any transaction in progress and :term:`releases` any :class:`_engine.Connection` objects which this :class:`_orm.Session` itself has checked out from associated :class:`_engine.Engine` objects. The operation then leaves the :class:`_orm.Session` in a state which it may be used again. .. tip:: The :meth:`_orm.Session.close` method **does not prevent the Session from being used again**. The :class:`_orm.Session` itself does not actually have a distinct "closed" state; it merely means the :class:`_orm.Session` will release all database connections and ORM objects. .. versionchanged:: 1.4 The :meth:`.Session.close` method does not immediately create a new :class:`.SessionTransaction` object; instead, the new :class:`.SessionTransaction` is created only if the :class:`.Session` is used again for a database operation. .. seealso:: :ref:`session_closing` - detail on the semantics of :meth:`_orm.Session.close`

Flush pending changes and commit the current transaction. When the COMMIT operation is complete, all objects are fully :term:`expired`, erasing their internal contents, which will be automatically re-loaded when the objects are next accessed. In the interim, these objects are in an expired state and will not function if they are :term:`detached` from the :class:`.Session`. Additionally, this re-load operation is not supported when using asyncio-oriented APIs. The :paramref:`.Session.expire_on_commit` parameter may be used to disable this behavior. When there is no transaction in place for the :class:`.Session`, indicating that no operations were invoked on this :class:`.Session` since the previous call to :meth:`.Session.commit`, the method will begin and commit an internal-only "logical" transaction, that does not normally affect the database unless pending flush changes were detected, but will still invoke event handlers and object expiration rules. The outermost database transaction is committed unconditionally, automatically releasing any SAVEPOINTs in effect. .. seealso:: :ref:`session_committing` :ref:`unitofwork_transaction` :ref:`asyncio_orm_avoid_lazyloads`

Return a :class:`_engine.Connection` object corresponding to this :class:`.Session` object's transactional state. Either the :class:`_engine.Connection` corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the :class:`_engine.Connection` returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted). 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_arguments: dictionary of bind arguments. May include "mapper", "bind", "clause", other custom arguments that are passed to :meth:`.Session.get_bind`. :param execution_options: a dictionary of execution options that will be passed to :meth:`_engine.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. .. seealso:: :ref:`session_transaction_isolation`

Mark an instance as deleted. The object is assumed to be either :term:`persistent` or :term:`detached` when passed; after the method is called, the object will remain in the :term:`persistent` state until the next flush proceeds. During this time, the object will also be a member of the :attr:`_orm.Session.deleted` collection. When the next flush proceeds, the object will move to the :term:`deleted` state, indicating a ``DELETE`` statement was emitted for its row within the current transaction. When the transaction is successfully committed, the deleted object is moved to the :term:`detached` state and is no longer present within this :class:`_orm.Session`. .. seealso:: :ref:`session_deleting` - at :ref:`session_basics`

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:`_orm.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:`_orm.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:: :paramref:`_orm.relationship.load_on_pending` - 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.

Execute a SQL expression construct. Returns a :class:`_engine.Result` object representing results of the statement execution. E.g.:: from sqlalchemy import select result = session.execute( select(User).where(User.id == 5) ) The API contract of :meth:`_orm.Session.execute` is similar to that of :meth:`_engine.Connection.execute`, the :term:`2.0 style` version of :class:`_engine.Connection`. .. versionchanged:: 1.4 the :meth:`_orm.Session.execute` method is now the primary point of ORM statement execution when using :term:`2.0 style` ORM usage. :param statement: An executable statement (i.e. an :class:`.Executable` expression such as :func:`_expression.select`). :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 execution_options: optional dictionary of execution options, which will be associated with the statement execution. This dictionary can provide a subset of the options that are accepted by :meth:`_engine.Connection.execution_options`, and may also provide additional options understood only in an ORM context. .. seealso:: :ref:`orm_queryguide_execution_options` - ORM-specific execution options :param bind_arguments: dictionary of additional arguments to determine the bind. May include "mapper", "bind", or other custom arguments. Contents of this dictionary are passed to the :meth:`.Session.get_bind` method. :return: a :class:`_engine.Result` object.

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` :meth:`_orm.Query.populate_existing`

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` is not usually needed, assuming the transaction is isolated. .. seealso:: :ref:`session_expire` - introductory material :meth:`.Session.expire` :meth:`.Session.refresh` :meth:`_orm.Query.populate_existing`

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.

Remove all object instances from this ``Session``. This is equivalent to calling ``expunge(obj)`` on all objects in this ``Session``.

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. :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.

Return an instance based on the given primary key identifier, or ``None`` if not found. E.g.:: my_user = session.get(User, 5) some_object = session.get(VersionedFoo, (5, 10)) some_object = session.get( VersionedFoo, {"id": 5, "version_id": 10} ) .. versionadded:: 1.4 Added :meth:`_orm.Session.get`, which is moved from the now legacy :meth:`_orm.Query.get` method. :meth:`_orm.Session.get` is special in that it provides direct access to the identity map of the :class:`.Session`. If the given primary key identifier is present in the local identity map, the object is returned directly from this collection and no SQL is emitted, unless the object has been marked fully expired. If not present, a SELECT is performed in order to locate the object. :meth:`_orm.Session.get` also will perform a check if the object is present in the identity map and marked as expired - a SELECT is emitted to refresh the object as well as to ensure that the row is still present. If not, :class:`~sqlalchemy.orm.exc.ObjectDeletedError` is raised. :param entity: a mapped class or :class:`.Mapper` indicating the type of entity to be loaded. :param ident: A scalar, tuple, or dictionary representing the primary key. For a composite (e.g. multiple column) primary key, a tuple or dictionary should be passed. For a single-column primary key, the scalar calling form is typically the most expedient. If the primary key of a row is the value "5", the call looks like:: my_object = session.get(SomeClass, 5) The tuple form contains primary key values typically in the order in which they correspond to the mapped :class:`_schema.Table` object's primary key columns, or if the :paramref:`_orm.Mapper.primary_key` configuration parameter were used, in the order used for that parameter. For example, if the primary key of a row is represented by the integer digits "5, 10" the call would look like:: my_object = session.get(SomeClass, (5, 10)) The dictionary form should include as keys the mapped attribute names corresponding to each element of the primary key. If the mapped class has the attributes ``id``, ``version_id`` as the attributes which store the object's primary key value, the call would look like:: my_object = session.get(SomeClass, {"id": 5, "version_id": 10}) :param options: optional sequence of loader options which will be applied to the query, if one is emitted. :param populate_existing: causes the method to unconditionally emit a SQL query and refresh the object with the newly loaded data, regardless of whether or not the object is already present. :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.Query.with_for_update`. Supersedes the :paramref:`.Session.refresh.lockmode` parameter. :param execution_options: optional dictionary of execution options, which will be associated with the query execution if one is emitted. This dictionary can provide a subset of the options that are accepted by :meth:`_engine.Connection.execution_options`, and may also provide additional options understood only in an ORM context. .. versionadded:: 1.4.29 .. seealso:: :ref:`orm_queryguide_execution_options` - ORM-specific execution options :param bind_arguments: dictionary of additional arguments to determine the bind. May include "mapper", "bind", or other custom arguments. Contents of this dictionary are passed to the :meth:`.Session.get_bind` method. .. versionadded: 2.0.0rc1 :return: The object instance, or ``None``.

Return a "bind" to which this :class:`.Session` is bound. The "bind" is usually an instance of :class:`_engine.Engine`, except in the case where the :class:`.Session` has been explicitly bound directly to a :class:`_engine.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 :paramref:`.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:`_schema.Table` objects found in the given clause present in ``Session.binds``. 3. if ``Session.binds`` is present, return that. 4. if clause given, attempt to return a bind linked to the :class:`_schema.MetaData` ultimately associated with the clause. 5. if mapper given, attempt to return a bind linked to the :class:`_schema.MetaData` ultimately associated with the :class:`_schema.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 mapped class or corresponding :class:`_orm.Mapper` instance. The bind can be derived from a :class:`_orm.Mapper` first by consulting the "binds" map associated with this :class:`.Session`, and secondly by consulting the :class:`_schema.MetaData` associated with the :class:`_schema.Table` to which the :class:`_orm.Mapper` is mapped for a bind. :param clause: A :class:`_expression.ClauseElement` (i.e. :func:`_expression.select`, :func:`_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:`_schema.Table` associated with bound :class:`_schema.MetaData`. .. seealso:: :ref:`session_partitioning` :paramref:`.Session.binds` :meth:`.Session.bind_mapper` :meth:`.Session.bind_table`

Return the current nested transaction in progress, if any. .. versionadded:: 1.4

Return the current root transaction in progress, if any. .. versionadded:: 1.4

Return True if this :class:`_orm.Session` has begun a nested transaction, e.g. SAVEPOINT. .. versionadded:: 1.4

Return True if this :class:`_orm.Session` has begun a transaction. .. versionadded:: 1.4 .. seealso:: :attr:`_orm.Session.is_active`

Close this Session, using connection invalidation. This is a variant of :meth:`.Session.close` that will additionally ensure that the :meth:`_engine.Connection.invalidate` method will be called on each :class:`_engine.Connection` object that is currently in use for a transaction (typically there is only one connection unless the :class:`_orm.Session` is used with multiple engines). This can be called when the database is known to be in a state where the connections are no longer safe to be used. Below illustrates a scenario when using `gevent <https://www.gevent.org/>`_, which can produce ``Timeout`` exceptions that may mean the underlying connection should be discarded:: import gevent try: sess = Session() sess.add(User()) sess.commit() except gevent.Timeout: sess.invalidate() raise except: sess.rollback() raise The method additionally does everything that :meth:`_orm.Session.close` does, including that all ORM objects are expunged.

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.

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. :param options: optional sequence of loader options which will be applied to the :meth:`_orm.Session.get` method when the merge operation loads the existing version of the object from the database. .. versionadded:: 1.4.24 .. seealso:: :func:`.make_transient_to_detached` - provides for an alternative means of "merging" a single object into the :class:`.Session`

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.

Return a new :class:`_query.Query` object corresponding to this :class:`_orm.Session`. Note that the :class:`_query.Query` object is legacy as of SQLAlchemy 2.0; the :func:`_sql.select` construct is now used to construct ORM queries. .. seealso:: :ref:`unified_tutorial` :ref:`queryguide_toplevel` :ref:`query_api_toplevel` - legacy API doc

Expire and refresh attributes on the given instance. The selected attributes will first be expired as they would when using :meth:`_orm.Session.expire`; then a SELECT statement will be issued to the database to refresh column-oriented attributes with the current value available in the current transaction. :func:`_orm.relationship` oriented attributes will also be immediately loaded if they were already eagerly loaded on the object, using the same eager loading strategy that they were loaded with originally. .. versionadded:: 1.4 - the :meth:`_orm.Session.refresh` method can also refresh eagerly loaded attributes. :func:`_orm.relationship` oriented attributes that would normally load using the ``select`` (or "lazy") loader strategy will also load **if they are named explicitly in the attribute_names collection**, emitting a SELECT statement for the attribute using the ``immediate`` loader strategy. If lazy-loaded relationships are not named in :paramref:`_orm.Session.refresh.attribute_names`, then they remain as "lazy loaded" attributes and are not implicitly refreshed. .. versionchanged:: 2.0.4 The :meth:`_orm.Session.refresh` method will now refresh lazy-loaded :func:`_orm.relationship` oriented attributes for those which are named explicitly in the :paramref:`_orm.Session.refresh.attribute_names` collection. .. tip:: While the :meth:`_orm.Session.refresh` method is capable of refreshing both column and relationship oriented attributes, its primary focus is on refreshing of local column-oriented attributes on a single instance. For more open ended "refresh" functionality, including the ability to refresh the attributes on many objects at once while having explicit control over relationship loader strategies, use the :ref:`populate existing <orm_queryguide_populate_existing>` feature instead. 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. Refreshing attributes usually only makes sense at the start of a transaction where database rows have not yet been accessed. :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.Query.with_for_update`. Supersedes the :paramref:`.Session.refresh.lockmode` parameter. .. seealso:: :ref:`session_expire` - introductory material :meth:`.Session.expire` :meth:`.Session.expire_all` :ref:`orm_queryguide_populate_existing` - allows any ORM query to refresh objects as they would be loaded normally.

Rollback the current transaction in progress. If no transaction is in progress, this method is a pass-through. The method always rolls back the topmost database transaction, discarding any nested transactions that may be in progress. .. seealso:: :ref:`session_rollback` :ref:`unitofwork_transaction`

Execute a statement and return a scalar result. Usage and parameters are the same as that of :meth:`_orm.Session.execute`; the return result is a scalar Python value.

Execute a statement and return the results as scalars. Usage and parameters are the same as that of :meth:`_orm.Session.execute`; the return result is a :class:`_result.ScalarResult` filtering object which will return single elements rather than :class:`_row.Row` objects. :return: a :class:`_result.ScalarResult` object .. versionadded:: 1.4.24 Added :meth:`_orm.Session.scalars` .. versionadded:: 1.4.26 Added :meth:`_orm.scoped_session.scalars` .. seealso:: :ref:`orm_queryguide_select_orm_entities` - contrasts the behavior of :meth:`_orm.Session.execute` to :meth:`_orm.Session.scalars`