sqlalchemy.orm.session.sessionmaker(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)¶Bases: sqlalchemy.orm.session._SessionClassMethods
A configurable Session factory.
The sessionmaker factory generates new
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 configure(), which can
be used to specify additional keyword arguments to the factory, which
will take effect for subsequent Session objects generated.
This is usually used to associate one or more Engine objects
with an existing sessionmaker factory before it is first
used:
# application starts
Session = sessionmaker()
# ... later
engine = create_engine('sqlite:///foo.db')
Session.configure(bind=engine)
sess = Session()__call__(**local_kw)¶Produce a new Session object using the configuration
established in this 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__()__eq__¶__eq__ attribute of objectReturn self==value.
__init__(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)¶Construct a new sessionmaker.
All arguments here except for class_ correspond to arguments
accepted by Session directly. See the
Session.__init__() docstring for more details on parameters.
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__le__¶__le__ attribute of objectReturn self<=value.
__lt__¶__lt__ attribute of objectReturn self<value.
__ne__¶__ne__ attribute of objectReturn self!=value.
close_all()¶close_all() method of _SessionClassMethodsDeprecated since version 1.3: The Session.close_all() method is deprecated and will be removed in a future release. Please refer to session.close_all_sessions().
Close all sessions in memory.
configure(**new_kw)¶(Re)configure the arguments for this sessionmaker.
e.g.:
Session = sessionmaker()
Session.configure(bind=create_engine('sqlite://'))identity_key(orm_util, *args, **kwargs)¶identity_key() method of _SessionClassMethodsReturn an identity key.
This is an alias of util.identity_key().
object_session(instance)¶object_session() method of _SessionClassMethodsReturn the Session to which an object belongs.
This is an alias of object_session().
sqlalchemy.orm.session.Session(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)¶Bases: sqlalchemy.orm.session._SessionClassMethods
Manages persistence operations for ORM-mapped objects.
The Session’s usage paradigm is described at Using the Session.
__eq__¶__eq__ attribute of objectReturn self==value.
__init__(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)¶Construct a new Session.
See also the sessionmaker function which is used to
generate a Session-producing callable with a given
set of arguments.
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__le__¶__le__ attribute of objectReturn self<=value.
__lt__¶__lt__ attribute of objectReturn self<value.
__ne__¶__ne__ attribute of objectReturn self!=value.
add(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().
add_all(instances)¶Add the given collection of instances to this Session.
begin(subtransactions=False, nested=False)¶Begin a transaction on this Session.
Warning
The Session.begin() method is part of a larger pattern
of use with the Session known as autocommit mode.
This is essentially a legacy mode of use and is
not necessary for new applications. The 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 Session programming patterns.
In its default mode of autocommit=False, the
Session does all of its work within
the context of a transaction, so as soon as you call
Session.commit(), the next transaction is implicitly
started when the next database operation is invoked. See
Autocommit Mode for further background.
The method will raise an error if this Session is already
inside of a transaction, unless
subtransactions or
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
Using Subtransactions with Autocommit.
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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 Using SAVEPOINT.
| Returns: | the SessionTransaction object. Note that
SessionTransaction acts as a context manager, allowing
Session.begin_nested() to be used in a “with” block.
See Using SAVEPOINT for a usage example. |
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See also
Serializable isolation / Savepoints / Transactional DDL - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly.
bind_mapper(mapper, bind)¶Associate a Mapper or arbitrary Python class with a
“bind”, e.g. an Engine or Connection.
The given entity is added to a lookup used by the
Session.get_bind() method.
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bind_table(table, bind)¶Associate a Table with a “bind”, e.g. an Engine
or Connection.
The given Table is added to a lookup used by the
Session.get_bind() method.
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bulk_insert_mappings(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 Insert() constructs, after
organizing the values within them across the tables to which
the given mapper is mapped.
New in version 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 Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.
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bulk_save_objects(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.
New in version 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 Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.
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bulk_update_mappings(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.
New in version 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 Bulk Operations before using this method, and fully test and confirm the functionality of all code developed using these systems.
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close()¶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.
close_all()¶close_all() method of _SessionClassMethodsDeprecated since version 1.3: The Session.close_all() method is deprecated and will be removed in a future release. Please refer to session.close_all_sessions().
Close all sessions in memory.
commit()¶Flush pending changes and commit the current transaction.
If no transaction is in progress, this method raises an
InvalidRequestError.
By default, the 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 sessionmaker or
the 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 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.
See also
connection(mapper=None, clause=None, bind=None, close_with_result=False, execution_options=None, **kw)¶Return a Connection object corresponding to this
Session object’s transactional state.
If this Session is configured with autocommit=False,
either the Connection corresponding to the current
transaction is returned, or if no transaction is in progress, a new
one is begun and the Connection returned (note that no
transactional state is established with the DBAPI until the first
SQL statement is emitted).
Alternatively, if this Session is configured with
autocommit=True, an ad-hoc Connection is returned
using Engine.connect() on the underlying
Engine.
Ambiguity in multi-bind or unbound Session objects can be
resolved through any of the optional keyword arguments. This
ultimately makes usage of the get_bind() method for resolution.
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delete(instance)¶Mark an instance as deleted.
The database delete operation occurs upon flush().
deleted¶The set of all instances marked as ‘deleted’ within this Session
dirty¶The set of all persistent instances considered dirty.
E.g.:
some_mapped_object in session.dirtyInstances 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 Session.is_modified() method.
enable_relationship_loading(obj)¶Associate an object with this Session for related
object loading.
Warning
enable_relationship_loading() exists to serve special
use cases and is not recommended for general use.
Accesses of attributes mapped with relationship()
will attempt to load a value from the database using this
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 Session.enable_relationship_loading() method is
similar to the load_on_pending flag on relationship().
Unlike that flag, 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 Session
via Session.enable_relationship_loading() pending, add
it to the Session using Session.add() normally.
If the object instead represents an existing identity in the database,
it should be merged using Session.merge().
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.
See also
load_on_pending at relationship() - this flag
allows per-relationship loading of many-to-ones on items that
are pending.
make_transient_to_detached() - allows for an object to
be added to a Session without SQL emitted, which then
will unexpire attributes on access.
execute(clause, params=None, mapper=None, bind=None, **kw)¶Execute a SQL expression construct or string statement within the current transaction.
Returns a ResultProxy representing
results of the statement execution, in the same manner as that of an
Engine or
Connection.
E.g.:
result = session.execute(
user_table.select().where(user_table.c.id == 5)
)execute() accepts any executable clause construct,
such as select(),
insert(),
update(),
delete(), and
text(). Plain SQL strings can be passed
as well, which in the case of Session.execute() only
will be interpreted the same as if it were passed via a
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 Session.execute() is an
optional parameter set. Similar to that of
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 Session. The Connection which is used
to execute the statement can also be acquired directly by
calling the Session.connection() method. Both methods use
a rule-based resolution scheme in order to determine the
Connection, which in the average case is derived directly
from the “bind” of the Session itself, and in other cases
can be based on the mapper()
and Table objects passed to the method; see the
documentation for Session.get_bind() for a full description of
this scheme.
The Session.execute() method does not invoke autoflush.
The ResultProxy returned by the Session.execute()
method is returned with the “close_with_result” flag set to true;
the significance of this flag is that if this Session is
autocommitting and does not have a transaction-dedicated
Connection available, a temporary Connection is
established for the statement execution, which is closed (meaning,
returned to the connection pool) when the ResultProxy has
consumed all available data. This applies only when the
Session is configured with autocommit=True and no
transaction has been started.
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See also
SQL Expression Language Tutorial - Tutorial on using Core SQL constructs.
Working with Engines and Connections - Further information on direct statement execution.
Connection.execute() - core level statement execution
method, which is Session.execute() ultimately uses
in order to execute the statement.
expire(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
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 Session simultaneously,
use Session.expire_all().
The Session object’s default behavior is to
expire all state whenever the Session.rollback()
or Session.commit() methods are called, so that new
state can be loaded for the new transaction. For this reason,
calling Session.expire() only makes sense for the specific
case that a non-ORM SQL statement was emitted in the current
transaction.
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expire_all()¶Expires all persistent instances within this Session.
When any attributes on a persistent instance is next accessed,
a query will be issued using the
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 Session.expire().
The Session object’s default behavior is to
expire all state whenever the Session.rollback()
or Session.commit() methods are called, so that new
state can be loaded for the new transaction. For this reason,
calling Session.expire_all() should not be needed when
autocommit is False, assuming the transaction is isolated.
expunge(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.
expunge_all()¶Remove all object instances from this Session.
This is equivalent to calling expunge(obj) on all objects in this
Session.
flush(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.
| Parameters: | 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. |
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get_bind(mapper=None, clause=None)¶Return a “bind” to which this Session is bound.
The “bind” is usually an instance of Engine,
except in the case where the Session has been
explicitly bound directly to a Connection.
For a multiply-bound or unbound Session, the
mapper or clause arguments are used to determine the
appropriate bind to return.
Note that the “mapper” argument is usually present
when Session.get_bind() is called via an ORM
operation such as a Session.query(), each
individual INSERT/UPDATE/DELETE operation within a
Session.flush(), call, etc.
The order of resolution is:
__mro__ of the mapped class, from more specific
superclasses to more general.Table objects
found in the given clause present in session.binds.MetaData ultimately
associated with the clause.MetaData ultimately
associated with the Table or other
selectable to which the mapper is mapped.UnboundExecutionError
is raised.Note that the Session.get_bind() method can be overridden on
a user-defined subclass of Session to provide any kind
of bind resolution scheme. See the example at
Custom Vertical Partitioning.
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identity_key(orm_util, *args, **kwargs)¶identity_key() method of _SessionClassMethodsReturn an identity key.
This is an alias of util.identity_key().
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.
See also
identity_key() - helper function to produce the keys used
in this dictionary.
info¶A user-modifiable dictionary.
The initial value of this dictionary can be populated using the
info argument to the Session constructor or
sessionmaker constructor or factory methods. The dictionary
here is always local to this Session and can be modified
independently of all other Session objects.
New in version 0.9.0.
invalidate()¶Close this Session, using connection invalidation.
This is a variant of Session.close() that will additionally
ensure that the Connection.invalidate() method will be called
on all 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()
raiseThis 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.
New in version 0.9.9.
is_active¶True if this Session is in “transaction mode” and
is not in “partial rollback” state.
The Session in its default mode of autocommit=False
is essentially always in “transaction mode”, in that a
SessionTransaction is associated with it as soon as
it is instantiated. This 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
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
Session has actually begun to use DBAPI resources is to
implement a listener using the SessionEvents.after_begin()
method, which will deliver both the Session as well as the
target 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
Session is in “partial rollback” and awaits for the user to
call Session.rollback(), in order to close out the
transaction stack. It is in this “partial rollback” period that the
is_active flag returns False. After the call to
Session.rollback(), the SessionTransaction is
replaced with a new one and is_active returns True again.
When a Session is used in autocommit=True mode, the
SessionTransaction is only instantiated within the scope
of a flush call, or when Session.begin() is called. So
is_active will always be False outside of a flush or
Session.begin() block in this mode, and will be True
within the 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 if a “rollback” is
necessary within a generic error handling routine, for
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
Session.rollback() unconditionally within the outermost
exception catch.
To track the transactional state of a Session fully,
use event listeners, primarily the SessionEvents.after_begin(),
SessionEvents.after_commit(),
SessionEvents.after_rollback() and related events.
is_modified(instance, include_collections=True, passive=None)¶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
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 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 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 column_property().
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merge(instance, load=True)¶Copy the state of a given instance into a corresponding instance
within this Session.
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 Session if not already.
This operation cascades to associated instances if the association is
mapped with cascade="merge".
See Merging for a detailed discussion of merging.
Changed in version 1.1: - Session.merge() will now reconcile
pending objects with overlapping primary keys in the same way
as persistent. See Session.merge resolves pending conflicts the same as persistent for discussion.
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See also
make_transient_to_detached() - provides for an alternative
means of “merging” a single object into the Session
new¶The set of all instances marked as ‘new’ within this Session.
no_autoflush¶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.
object_session(instance)¶object_session() method of _SessionClassMethodsReturn the Session to which an object belongs.
This is an alias of object_session().
prepare()¶Prepare the current transaction in progress for two phase commit.
If no transaction is in progress, this method raises an
InvalidRequestError.
Only root transactions of two phase sessions can be prepared. If the
current transaction is not such, an
InvalidRequestError is raised.
prune()¶Remove unreferenced instances cached in the identity map.
Deprecated since version 0.7: The Session.prune() method is deprecated along with Session.weak_identity_map. This method will be removed in a future release.
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.
refresh(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
refresh() usually only makes sense if non-ORM SQL
statement were emitted in the ongoing transaction, or if autocommit
mode is turned on.
| Parameters: |
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rollback()¶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
begin() is called multiple times.
See also
scalar(clause, params=None, mapper=None, bind=None, **kw)¶Like execute() but return a scalar result.
transaction = None¶The current active or inactive SessionTransaction.
sqlalchemy.orm.session.SessionTransaction(session, parent=None, nested=False)¶A Session-level transaction.
SessionTransaction is a mostly behind-the-scenes object
not normally referenced directly by application code. It coordinates
among multiple 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 Session.transaction attribute of Session
refers to the current SessionTransaction object in use, if any.
The SessionTransaction.parent attribute refers to the parent
SessionTransaction in the stack of SessionTransaction
objects. If this attribute is None, then this is the top of the stack.
If non-None, then this 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 SessionTransaction.nested
attribute is also True, indicates that this SessionTransaction
corresponds to a SAVEPOINT.
Life Cycle
A SessionTransaction is associated with a Session
in its default mode of autocommit=False immediately, associated
with no database connections. As the Session is called upon
to emit SQL on behalf of various Engine or Connection
objects, a corresponding Connection and associated
Transaction is added to a collection within the
SessionTransaction object, becoming one of the
connection/transaction pairs maintained by the
SessionTransaction. The start of a SessionTransaction
can be tracked using the SessionEvents.after_transaction_create()
event.
The lifespan of the SessionTransaction ends when the
Session.commit(), Session.rollback() or
Session.close() methods are called. At this point, the
SessionTransaction removes its association with its parent
Session. A Session that is in autocommit=False
mode will create a new SessionTransaction to replace it
immediately, whereas a Session that’s in autocommit=True
mode will remain without a SessionTransaction until the
Session.begin() method is called. The end of a
SessionTransaction can be tracked using the
SessionEvents.after_transaction_end() event.
Nesting and Subtransactions
Another detail of SessionTransaction behavior is that it is
capable of “nesting”. This means that the Session.begin() method
can be called while an existing SessionTransaction is already
present, producing a new SessionTransaction that temporarily
replaces the parent SessionTransaction. When a
SessionTransaction is produced as nested, it assigns itself to
the Session.transaction attribute, and it additionally will assign
the previous SessionTransaction to its Session.parent
attribute. The behavior is effectively a
stack, where Session.transaction refers to the current head of
the stack, and the SessionTransaction.parent attribute allows
traversal up the stack until SessionTransaction.parent is
None, indicating the top of the stack.
When the scope of SessionTransaction is ended via
Session.commit() or Session.rollback(), it restores its
parent SessionTransaction back onto the
Session.transaction attribute.
The purpose of this stack is to allow nesting of
Session.rollback() or Session.commit() calls in context
with various flavors of Session.begin(). This nesting behavior
applies to when 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 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
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 Session.flush() method is used always
creates a SessionTransaction object. This object is normally
a subtransaction, unless the 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 SessionTransaction
is the outermost transaction, a subtransaction, or a “nested” / SAVEPOINT
transaction.
See also
SessionEvents.after_transaction_create()
SessionEvents.after_transaction_end()
nested = False¶Indicates if this is a nested, or SAVEPOINT, transaction.
When SessionTransaction.nested is True, it is expected
that SessionTransaction.parent will be True as well.
parent¶The parent SessionTransaction of this
SessionTransaction.
If this attribute is None, indicates this
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
SessionTransaction.nested attribute is True, then
this is a SAVEPOINT, and if False, indicates this a subtransaction.
New in version 1.0.16: - use ._parent for previous versions
sqlalchemy.orm.session.close_all_sessions()¶Close all sessions in memory.
This function consults a global registry of all Session objects
and calls 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.
New in version 1.3.
sqlalchemy.orm.session.make_transient(instance)¶Alter the state of the given instance so that it is transient.
Note
make_transient() is a special-case function for
advanced use cases only.
The given mapped instance is assumed to be in the persistent or
detached state. The function will remove its association with any
Session as well as its 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 InstanceState.deleted flag is also reset
if this object had been deleted as a result of using
Session.delete().
Warning
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:
Session.expire()Session.commit()After 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.
See also
sqlalchemy.orm.session.make_transient_to_detached(instance)¶Make the given transient instance detached.
Note
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 Session.merge() in that a given persistent state
can be manufactured without any SQL calls.
New in version 0.9.5.
sqlalchemy.orm.session.object_session(instance)¶Return the Session to which the given instance belongs.
This is essentially the same as the InstanceState.session
accessor. See that attribute for details.
sqlalchemy.orm.util.was_deleted(object_)¶Return True if the given object was deleted within a session flush.
This is regardless of whether or not the object is persistent or detached.
See also
These functions are provided by the SQLAlchemy attribute instrumentation API to provide a detailed interface for dealing with instances, attribute values, and history. Some of them are useful when constructing event listener functions, such as those described in ORM Events.
sqlalchemy.orm.util.object_state(instance)¶Given an object, return the InstanceState
associated with the object.
Raises sqlalchemy.orm.exc.UnmappedInstanceError
if no mapping is configured.
Equivalent functionality is available via the inspect()
function as:
inspect(instance)Using the inspection system will raise
sqlalchemy.exc.NoInspectionAvailable if the instance is
not part of a mapping.
sqlalchemy.orm.attributes.del_attribute(instance, key)¶Delete the value of an attribute, firing history events.
This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.
sqlalchemy.orm.attributes.get_attribute(instance, key)¶Get the value of an attribute, firing any callables required.
This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to make usage of attribute state as understood by SQLAlchemy.
sqlalchemy.orm.attributes.get_history(obj, key, passive=symbol('PASSIVE_OFF'))¶Return a History record for the given object
and attribute key.
This is the pre-flush history for a given attribute, which is
reset each time the Session flushes changes to the
current database transaction.
Note
Prefer to use the AttributeState.history and
AttributeState.load_history() accessors to retrieve the
History for instance attributes.
| Parameters: |
|
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See also
AttributeState.load_history() - retrieve history
using loader callables if the value is not locally present.
sqlalchemy.orm.attributes.init_collection(obj, key)¶Initialize a collection attribute and return the collection adapter.
This function is used to provide direct access to collection internals for a previously unloaded attribute. e.g.:
collection_adapter = init_collection(someobject, 'elements')
for elem in values:
collection_adapter.append_without_event(elem)For an easier way to do the above, see
set_committed_value().
| Parameters: |
|---|
sqlalchemy.orm.attributes.flag_modified(instance, key)¶Mark an attribute on an instance as ‘modified’.
This sets the ‘modified’ flag on the instance and
establishes an unconditional change event for the given attribute.
The attribute must have a value present, else an
InvalidRequestError is raised.
To mark an object “dirty” without referring to any specific attribute
so that it is considered within a flush, use the
attributes.flag_dirty() call.
See also
sqlalchemy.orm.attributes.flag_dirty(instance)¶Mark an instance as ‘dirty’ without any specific attribute mentioned.
This is a special operation that will allow the object to travel through
the flush process for interception by events such as
SessionEvents.before_flush(). Note that no SQL will be emitted in
the flush process for an object that has no changes, even if marked dirty
via this method. However, a SessionEvents.before_flush() handler
will be able to see the object in the Session.dirty collection and
may establish changes on it, which will then be included in the SQL
emitted.
New in version 1.2.
See also
sqlalchemy.orm.attributes.instance_state()¶Return the InstanceState for a given
mapped object.
This function is the internal version
of object_state(). The
object_state() and/or the
inspect() function is preferred here
as they each emit an informative exception
if the given object is not mapped.
sqlalchemy.orm.instrumentation.is_instrumented(instance, key)¶Return True if the given attribute on the given instance is instrumented by the attributes package.
This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required.
sqlalchemy.orm.attributes.set_attribute(instance, key, value, initiator=None)¶Set the value of an attribute, firing history events.
This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.
| Parameters: |
|
|---|
sqlalchemy.orm.attributes.set_committed_value(instance, key, value)¶Set the value of an attribute with no history events.
Cancels any previous history present. The value should be a scalar value for scalar-holding attributes, or an iterable for any collection-holding attribute.
This is the same underlying method used when a lazy loader fires off and loads additional data from the database. In particular, this method can be used by application code which has loaded additional attributes or collections through separate queries, which can then be attached to an instance as though it were part of its original loaded state.
sqlalchemy.orm.attributes.History¶Bases: sqlalchemy.orm.attributes.History
A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.
The easiest way to get a History object for a particular
attribute on an object is to use the inspect() function:
from sqlalchemy import inspect
hist = inspect(myobject).attrs.myattribute.historyEach tuple member is an iterable sequence:
added - the collection of items added to the attribute (the first
tuple element).unchanged - the collection of items that have not changed on the
attribute (the second tuple element).deleted - the collection of items that have been removed from the
attribute (the third tuple element).non_added()¶Return a collection of unchanged + deleted.
non_deleted()¶Return a collection of added + unchanged.
sum()¶Return a collection of added + unchanged + deleted.