# orm/session.py # Copyright (C) 2005-2012 the SQLAlchemy authors and contributors # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Provides the Session class and related utilities.""" import weakref from itertools import chain from sqlalchemy import util, sql, engine, log, exc as sa_exc from sqlalchemy.sql import util as sql_util, expression from sqlalchemy.orm import ( SessionExtension, attributes, exc, query, unitofwork, util as mapperutil, state ) from sqlalchemy.orm.util import object_mapper as _object_mapper from sqlalchemy.orm.util import class_mapper as _class_mapper from sqlalchemy.orm.util import ( _class_to_mapper, _state_mapper, ) from sqlalchemy.orm.mapper import Mapper, _none_set from sqlalchemy.orm.unitofwork import UOWTransaction from sqlalchemy.orm import identity from sqlalchemy import event from sqlalchemy.orm.events import SessionEvents import sys __all__ = ['Session', 'SessionTransaction', 'SessionExtension'] def sessionmaker(bind=None, class_=None, autoflush=True, autocommit=False, expire_on_commit=True, **kwargs): """Generate a custom-configured :class:`.Session` class. The returned object is a subclass of :class:`.Session`, which, when instantiated with no arguments, uses the keyword arguments configured here as its constructor arguments. It is intended that the :func:`.sessionmaker()` function be called within the global scope of an application, and the returned class be made available to the rest of the application as the single class used to instantiate sessions. 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 special classmethod ``configure()``, which allows additional configurational options to take place after the custom ``Session`` class has been generated. This is useful particularly for defining the specific ``Engine`` (or engines) to which new instances of ``Session`` should be bound:: Session = sessionmaker() Session.configure(bind=create_engine('sqlite:///foo.db')) sess = Session() For options, see the constructor options for :class:`.Session`. """ kwargs['bind'] = bind kwargs['autoflush'] = autoflush kwargs['autocommit'] = autocommit kwargs['expire_on_commit'] = expire_on_commit if class_ is None: class_ = Session class Sess(object): def __init__(self, **local_kwargs): for k in kwargs: local_kwargs.setdefault(k, kwargs[k]) super(Sess, self).__init__(**local_kwargs) @classmethod def configure(self, **new_kwargs): """(Re)configure the arguments for this sessionmaker. e.g.:: Session = sessionmaker() Session.configure(bind=create_engine('sqlite://')) """ kwargs.update(new_kwargs) return type("SessionMaker", (Sess, class_), {}) class SessionTransaction(object): """A Session-level transaction. This corresponds to one or more Core :class:`~.engine.base.Transaction` instances behind the scenes, with one :class:`~.engine.base.Transaction` per :class:`~.engine.base.Engine` in use. Direct usage of :class:`.SessionTransaction` is not typically necessary as of SQLAlchemy 0.4; use the :meth:`.Session.rollback` and :meth:`.Session.commit` methods on :class:`.Session` itself to control the transaction. The current instance of :class:`.SessionTransaction` for a given :class:`.Session` is available via the :attr:`.Session.transaction` attribute. The :class:`.SessionTransaction` object is **not** thread-safe. See also: :meth:`.Session.rollback` :meth:`.Session.commit` :attr:`.Session.is_active` :meth:`.SessionEvents.after_commit` :meth:`.SessionEvents.after_rollback` :meth:`.SessionEvents.after_soft_rollback` .. index:: single: thread safety; SessionTransaction """ _rollback_exception = None def __init__(self, session, parent=None, nested=False): self.session = session self._connections = {} self._parent = parent self.nested = nested self._active = True self._prepared = False if not parent and nested: raise sa_exc.InvalidRequestError( "Can't start a SAVEPOINT transaction when no existing " "transaction is in progress") if self.session._enable_transaction_accounting: self._take_snapshot() @property def is_active(self): return self.session is not None and self._active def _assert_is_active(self): self._assert_is_open() if not self._active: if self._rollback_exception: raise sa_exc.InvalidRequestError( "This Session's transaction has been rolled back " "due to a previous exception during flush." " To begin a new transaction with this Session, " "first issue Session.rollback()." " Original exception was: %s" % self._rollback_exception ) else: raise sa_exc.InvalidRequestError( "This Session's transaction has been rolled back " "by a nested rollback() call. To begin a new " "transaction, issue Session.rollback() first." ) def _assert_is_open(self, error_msg="The transaction is closed"): if self.session is None: raise sa_exc.ResourceClosedError(error_msg) @property def _is_transaction_boundary(self): return self.nested or not self._parent def connection(self, bindkey, **kwargs): self._assert_is_active() engine = self.session.get_bind(bindkey, **kwargs) return self._connection_for_bind(engine) def _begin(self, nested=False): self._assert_is_active() return SessionTransaction( self.session, self, nested=nested) def _iterate_parents(self, upto=None): if self._parent is upto: return (self,) else: if self._parent is None: raise sa_exc.InvalidRequestError( "Transaction %s is not on the active transaction list" % ( upto)) return (self,) + self._parent._iterate_parents(upto) def _take_snapshot(self): if not self._is_transaction_boundary: self._new = self._parent._new self._deleted = self._parent._deleted return if not self.session._flushing: self.session.flush() self._new = weakref.WeakKeyDictionary() self._deleted = weakref.WeakKeyDictionary() def _restore_snapshot(self): assert self._is_transaction_boundary for s in set(self._new).union(self.session._new): self.session._expunge_state(s) if s.key: del s.key for s in set(self._deleted).union(self.session._deleted): if s.deleted: #assert s in self._deleted del s.deleted self.session._update_impl(s) assert not self.session._deleted for s in self.session.identity_map.all_states(): s.expire(s.dict, self.session.identity_map._modified) def _remove_snapshot(self): assert self._is_transaction_boundary if not self.nested and self.session.expire_on_commit: for s in self.session.identity_map.all_states(): s.expire(s.dict, self.session.identity_map._modified) def _connection_for_bind(self, bind): self._assert_is_active() if bind in self._connections: return self._connections[bind][0] if self._parent: conn = self._parent._connection_for_bind(bind) if not self.nested: return conn else: if isinstance(bind, engine.Connection): conn = bind if conn.engine in self._connections: raise sa_exc.InvalidRequestError( "Session already has a Connection associated for the " "given Connection's Engine") else: conn = bind.contextual_connect() if self.session.twophase and self._parent is None: transaction = conn.begin_twophase() elif self.nested: transaction = conn.begin_nested() else: transaction = conn.begin() self._connections[conn] = self._connections[conn.engine] = \ (conn, transaction, conn is not bind) self.session.dispatch.after_begin(self.session, self, conn) return conn def prepare(self): if self._parent is not None or not self.session.twophase: raise sa_exc.InvalidRequestError( "Only root two phase transactions of can be prepared") self._prepare_impl() def _prepare_impl(self): self._assert_is_active() if self._parent is None or self.nested: self.session.dispatch.before_commit(self.session) stx = self.session.transaction if stx is not self: for subtransaction in stx._iterate_parents(upto=self): subtransaction.commit() if not self.session._flushing: self.session.flush() if self._parent is None and self.session.twophase: try: for t in set(self._connections.values()): t[1].prepare() except: self.rollback() raise self._deactivate() self._prepared = True def commit(self): self._assert_is_open() if not self._prepared: self._prepare_impl() if self._parent is None or self.nested: for t in set(self._connections.values()): t[1].commit() self.session.dispatch.after_commit(self.session) if self.session._enable_transaction_accounting: self._remove_snapshot() self.close() return self._parent def rollback(self, _capture_exception=False): self._assert_is_open() stx = self.session.transaction if stx is not self: for subtransaction in stx._iterate_parents(upto=self): subtransaction.close() if self.is_active or self._prepared: for transaction in self._iterate_parents(): if transaction._parent is None or transaction.nested: transaction._rollback_impl() transaction._deactivate() break else: transaction._deactivate() sess = self.session if self.session._enable_transaction_accounting and \ not sess._is_clean(): # if items were added, deleted, or mutated # here, we need to re-restore the snapshot util.warn( "Session's state has been changed on " "a non-active transaction - this state " "will be discarded.") self._restore_snapshot() self.close() if self._parent and _capture_exception: self._parent._rollback_exception = sys.exc_info()[1] sess.dispatch.after_soft_rollback(sess, self) return self._parent def _rollback_impl(self): for t in set(self._connections.values()): t[1].rollback() if self.session._enable_transaction_accounting: self._restore_snapshot() self.session.dispatch.after_rollback(self.session) def _deactivate(self): self._active = False def close(self): self.session.transaction = self._parent if self._parent is None: for connection, transaction, autoclose in \ set(self._connections.values()): if autoclose: connection.close() else: transaction.close() if not self.session.autocommit: self.session.begin() self._deactivate() self.session = None self._connections = None def __enter__(self): return self def __exit__(self, type, value, traceback): self._assert_is_open("Cannot end transaction context. The transaction " "was closed from within the context") if self.session.transaction is None: return if type is None: try: self.commit() except: self.rollback() raise else: self.rollback() class Session(object): """Manages persistence operations for ORM-mapped objects. The Session's usage paradigm is described at :ref:`session_toplevel`. """ public_methods = ( '__contains__', '__iter__', 'add', 'add_all', 'begin', 'begin_nested', 'close', 'commit', 'connection', 'delete', 'execute', 'expire', 'expire_all', 'expunge', 'expunge_all', 'flush', 'get_bind', 'is_modified', 'merge', 'query', 'refresh', 'rollback', 'scalar') def __init__(self, bind=None, autoflush=True, expire_on_commit=True, _enable_transaction_accounting=True, autocommit=False, twophase=False, weak_identity_map=True, binds=None, extension=None, query_cls=query.Query): """Construct a new Session. See also the :func:`.sessionmaker` function which is used to generate a :class:`.Session`-producing callable with a given set of arguments. :param autocommit: Defaults to ``False``. When ``True``, the ``Session`` does not keep a persistent transaction running, and will acquire connections from the engine on an as-needed basis, returning them immediately after their use. Flushes will begin and commit (or possibly rollback) their own transaction if no transaction is present. When using this mode, the `session.begin()` method may be used to begin a transaction explicitly. Leaving it on its default value of ``False`` means that the ``Session`` will acquire a connection and begin a transaction the first time it is used, which it will maintain persistently until ``rollback()``, ``commit()``, or ``close()`` is called. When the transaction is released by any of these methods, the ``Session`` is ready for the next usage, which will again acquire and maintain a new connection/transaction. :param autoflush: When ``True``, all query operations will issue a ``flush()`` call to this ``Session`` before proceeding. This is a convenience feature so that ``flush()`` need not be called repeatedly in order for database queries to retrieve results. It's typical that ``autoflush`` is used in conjunction with ``autocommit=False``. In this scenario, explicit calls to ``flush()`` are rarely needed; you usually only need to call ``commit()`` (which flushes) to finalize changes. :param bind: An optional ``Engine`` or ``Connection`` to which this ``Session`` should be bound. When specified, all SQL operations performed by this session will execute via this connectable. :param binds: An optional dictionary which contains more granular "bind" information than the ``bind`` parameter provides. This dictionary can map individual ``Table`` instances as well as ``Mapper`` instances to individual ``Engine`` or ``Connection`` objects. Operations which proceed relative to a particular ``Mapper`` will consult this dictionary for the direct ``Mapper`` instance as well as the mapper's ``mapped_table`` attribute in order to locate an connectable to use. The full resolution is described in the ``get_bind()`` method of ``Session``. Usage looks like:: Session = sessionmaker(binds={ SomeMappedClass: create_engine('postgresql://engine1'), somemapper: create_engine('postgresql://engine2'), some_table: create_engine('postgresql://engine3'), }) Also see the :meth:`.Session.bind_mapper` and :meth:`.Session.bind_table` methods. :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 ``sessionmaker()`` function, and is not sent directly to the constructor for ``Session``. :param _enable_transaction_accounting: Defaults to ``True``. A legacy-only flag which when ``False`` disables *all* 0.5-style object accounting on transaction boundaries, including auto-expiry of instances on rollback and commit, maintenance of the "new" and "deleted" lists upon rollback, and autoflush of pending changes upon begin(), all of which are interdependent. :param expire_on_commit: Defaults to ``True``. When ``True``, all instances will be fully expired after each ``commit()``, so that all attribute/object access subsequent to a completed transaction will load from the most recent database state. :param extension: An optional :class:`~.SessionExtension` instance, or a list of such instances, which will receive pre- and post- commit and flush events, as well as a post-rollback event. **Deprecated.** Please see :class:`.SessionEvents`. :param query_cls: Class which should be used to create new Query objects, as returned by the ``query()`` method. Defaults to :class:`~sqlalchemy.orm.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 ``commit()``, after ``flush()`` has been issued for all attached databases, the ``prepare()`` method on each database's ``TwoPhaseTransaction`` will be called. This allows each database to roll back the entire transaction, before each transaction is committed. :param weak_identity_map: Defaults to ``True`` - when set to ``False``, objects placed in the :class:`.Session` will be strongly referenced until explicitly removed or the :class:`.Session` is closed. **Deprecated** - this option is obsolete. """ if weak_identity_map: self._identity_cls = identity.WeakInstanceDict else: util.warn_deprecated("weak_identity_map=False is deprecated. " "This feature is not needed.") self._identity_cls = identity.StrongInstanceDict self.identity_map = self._identity_cls() self._new = {} # InstanceState->object, strong refs object self._deleted = {} # same self.bind = bind self.__binds = {} self._flushing = False self.transaction = None self.hash_key = _new_sessionid() self.autoflush = autoflush self.autocommit = autocommit self.expire_on_commit = expire_on_commit self._enable_transaction_accounting = _enable_transaction_accounting self.twophase = twophase self._query_cls = query_cls if extension: for ext in util.to_list(extension): SessionExtension._adapt_listener(self, ext) if binds is not None: for mapperortable, bind in binds.iteritems(): if isinstance(mapperortable, (type, Mapper)): self.bind_mapper(mapperortable, bind) else: self.bind_table(mapperortable, bind) if not self.autocommit: self.begin() _sessions[self.hash_key] = self dispatch = event.dispatcher(SessionEvents) connection_callable = None transaction = None """The current active or inactive :class:`.SessionTransaction`.""" def begin(self, subtransactions=False, nested=False): """Begin a transaction on this Session. If this Session is already within a transaction, either a plain transaction or nested transaction, an error is raised, unless ``subtransactions=True`` or ``nested=True`` is specified. The ``subtransactions=True`` flag indicates that this :meth:`~.Session.begin` can create a subtransaction if a transaction is already in progress. For documentation on subtransactions, please see :ref:`session_subtransactions`. The ``nested`` flag begins a SAVEPOINT transaction and is equivalent to calling :meth:`~.Session.begin_nested`. For documentation on SAVEPOINT transactions, please see :ref:`session_begin_nested`. """ if self.transaction is not None: if subtransactions or nested: self.transaction = self.transaction._begin( nested=nested) else: raise sa_exc.InvalidRequestError( "A transaction is already begun. Use subtransactions=True " "to allow subtransactions.") else: self.transaction = SessionTransaction( self, nested=nested) return self.transaction # needed for __enter__/__exit__ hook def begin_nested(self): """Begin a `nested` transaction on this Session. The target database(s) must support SQL SAVEPOINTs or a SQLAlchemy-supported vendor implementation of the idea. For documentation on SAVEPOINT transactions, please see :ref:`session_begin_nested`. """ return self.begin(nested=True) def rollback(self): """Rollback the current transaction in progress. If no transaction is in progress, this method is a pass-through. This method rolls back the current transaction or nested transaction regardless of subtransactions being in effect. All subtransactions up to the first real transaction are closed. Subtransactions occur when begin() is called multiple times. """ if self.transaction is None: pass else: self.transaction.rollback() def commit(self): """Flush pending changes and commit the current transaction. If no transaction is in progress, this method raises an InvalidRequestError. By default, the :class:`.Session` also expires all database loaded state on all ORM-managed attributes after transaction commit. This so that subsequent operations load the most recent data from the database. This behavior can be disabled using the ``expire_on_commit=False`` option to :func:`.sessionmaker` or the :class:`.Session` constructor. If a subtransaction is in effect (which occurs when begin() is called multiple times), the subtransaction will be closed, and the next call to ``commit()`` will operate on the enclosing transaction. For a session configured with 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. """ if self.transaction is None: if not self.autocommit: self.begin() else: raise sa_exc.InvalidRequestError("No transaction is begun.") self.transaction.commit() def prepare(self): """Prepare the current transaction in progress for two phase commit. If no transaction is in progress, this method raises an InvalidRequestError. Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an InvalidRequestError is raised. """ if self.transaction is None: if not self.autocommit: self.begin() else: raise sa_exc.InvalidRequestError("No transaction is begun.") self.transaction.prepare() def connection(self, mapper=None, clause=None, bind=None, close_with_result=False, **kw): """Return a :class:`.Connection` object corresponding to this :class:`.Session` object's transactional state. If this :class:`.Session` is configured with ``autocommit=False``, either the :class:`.Connection` corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the :class:`.Connection` returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted). Alternatively, if this :class:`.Session` is configured with ``autocommit=True``, an ad-hoc :class:`.Connection` is returned using :meth:`.Engine.contextual_connect` on the underlying :class:`.Engine`. Ambiguity in multi-bind or unbound :class:`.Session` objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the :meth:`.get_bind` method for resolution. :param bind: Optional :class:`.Engine` to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over ``mapper``, ``clause``. :param mapper: Optional :func:`.mapper` mapped class, used to identify the appropriate bind. This argument takes precedence over ``clause``. :param clause: A :class:`.ClauseElement` (i.e. :func:`~.sql.expression.select`, :func:`~.sql.expression.text`, etc.) which will be used to locate a bind, if a bind cannot otherwise be identified. :param close_with_result: Passed to :meth:`Engine.connect`, indicating the :class:`.Connection` should be considered "single use", automatically closing when the first result set is closed. This flag only has an effect if this :class:`.Session` is configured with ``autocommit=True`` and does not already have a transaction in progress. :param \**kw: Additional keyword arguments are sent to :meth:`get_bind()`, allowing additional arguments to be passed to custom implementations of :meth:`get_bind`. """ if bind is None: bind = self.get_bind(mapper, clause=clause, **kw) return self._connection_for_bind(bind, close_with_result=close_with_result) def _connection_for_bind(self, engine, **kwargs): if self.transaction is not None: return self.transaction._connection_for_bind(engine) else: return engine.contextual_connect(**kwargs) def execute(self, clause, params=None, mapper=None, bind=None, **kw): """Execute a clause within the current transaction. Returns a :class:`.ResultProxy` representing results of the statement execution, in the same manner as that of an :class:`.Engine` or :class:`.Connection`. :meth:`~.Session.execute` accepts any executable clause construct, such as :func:`~.sql.expression.select`, :func:`~.sql.expression.insert`, :func:`~.sql.expression.update`, :func:`~.sql.expression.delete`, and :func:`~.sql.expression.text`, and additionally accepts plain strings that represent SQL statements. If a plain string is passed, it is first converted to a :func:`~.sql.expression.text` construct, which here means that bind parameters should be specified using the format ``:param``. If raw DBAPI statement execution is desired, use :meth:`.Session.connection` to acquire a :class:`.Connection`, then call its :meth:`~.Connection.execute` method. The statement is executed within the current transactional context of this :class:`.Session`, using the same behavior as that of the :meth:`.Session.connection` method to determine the active :class:`.Connection`. The ``close_with_result`` flag is set to ``True`` so that an ``autocommit=True`` :class:`.Session` with no active transaction will produce a result that auto-closes the underlying :class:`.Connection`. :param clause: A :class:`.ClauseElement` (i.e. :func:`~.sql.expression.select`, :func:`~.sql.expression.text`, etc.) or string SQL statement to be executed. The clause will also be used to locate a bind, if this :class:`.Session` is not bound to a single engine already, and the ``mapper`` and ``bind`` arguments are not passed. :param params: Optional dictionary of bind names mapped to values. :param mapper: Optional :func:`.mapper` or mapped class, used to identify the appropriate bind. This argument takes precedence over ``clause`` when locating a bind. :param bind: Optional :class:`.Engine` to be used as the bind. If this engine is already involved in an ongoing transaction, that connection will be used. This argument takes precedence over ``mapper`` and ``clause`` when locating a bind. :param \**kw: Additional keyword arguments are sent to :meth:`get_bind()`, allowing additional arguments to be passed to custom implementations of :meth:`get_bind`. """ clause = expression._literal_as_text(clause) if bind is None: bind = self.get_bind(mapper, clause=clause, **kw) return self._connection_for_bind(bind, close_with_result=True).execute( clause, params or {}) def scalar(self, clause, params=None, mapper=None, bind=None, **kw): """Like :meth:`~.Session.execute` but return a scalar result.""" return self.execute(clause, params=params, mapper=mapper, bind=bind, **kw).scalar() def close(self): """Close this Session. This clears all items and ends any transaction in progress. If this session were created with ``autocommit=False``, a new transaction is immediately begun. Note that this new transaction does not use any connection resources until they are first needed. """ self.expunge_all() if self.transaction is not None: for transaction in self.transaction._iterate_parents(): transaction.close() @classmethod def close_all(cls): """Close *all* sessions in memory.""" for sess in _sessions.values(): sess.close() def expunge_all(self): """Remove all object instances from this ``Session``. This is equivalent to calling ``expunge(obj)`` on all objects in this ``Session``. """ for state in self.identity_map.all_states() + list(self._new): state.detach() self.identity_map = self._identity_cls() self._new = {} self._deleted = {} # TODO: need much more test coverage for bind_mapper() and similar ! # TODO: + crystalize + document resolution order vis. bind_mapper/bind_table def bind_mapper(self, mapper, bind): """Bind operations for a mapper to a Connectable. mapper A mapper instance or mapped class bind Any Connectable: a ``Engine`` or ``Connection``. All subsequent operations involving this mapper will use the given `bind`. """ if isinstance(mapper, type): mapper = _class_mapper(mapper) self.__binds[mapper.base_mapper] = bind for t in mapper._all_tables: self.__binds[t] = bind def bind_table(self, table, bind): """Bind operations on a Table to a Connectable. table A ``Table`` instance bind Any Connectable: a ``Engine`` or ``Connection``. All subsequent operations involving this ``Table`` will use the given `bind`. """ self.__binds[table] = bind def get_bind(self, mapper=None, clause=None): """Return a "bind" to which this :class:`.Session` is bound. The "bind" is usually an instance of :class:`.Engine`, except in the case where the :class:`.Session` has been explicitly bound directly to a :class:`.Connection`. For a multiply-bound or unbound :class:`.Session`, the ``mapper`` or ``clause`` arguments are used to determine the appropriate bind to return. Note that the "mapper" argument is usually present when :meth:`.Session.get_bind` is called via an ORM operation such as a :meth:`.Session.query`, each individual INSERT/UPDATE/DELETE operation within a :meth:`.Session.flush`, call, etc. The order of resolution is: 1. if mapper given and session.binds is present, locate a bind based on mapper. 2. if clause given and session.binds is present, locate a bind based on :class:`.Table` objects found in the given clause present in session.binds. 3. if session.bind is present, return that. 4. if clause given, attempt to return a bind linked to the :class:`.MetaData` ultimately associated with the clause. 5. if mapper given, attempt to return a bind linked to the :class:`.MetaData` ultimately associated with the :class:`.Table` or other selectable to which the mapper is mapped. 6. No bind can be found, :class:`.UnboundExecutionError` is raised. :param mapper: Optional :func:`.mapper` mapped class or instance of :class:`.Mapper`. The bind can be derived from a :class:`.Mapper` first by consulting the "binds" map associated with this :class:`.Session`, and secondly by consulting the :class:`.MetaData` associated with the :class:`.Table` to which the :class:`.Mapper` is mapped for a bind. :param clause: A :class:`.ClauseElement` (i.e. :func:`~.sql.expression.select`, :func:`~.sql.expression.text`, etc.). If the ``mapper`` argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a :class:`.Table` associated with bound :class:`.MetaData`. """ if mapper is clause is None: if self.bind: return self.bind else: raise sa_exc.UnboundExecutionError( "This session is not bound to a single Engine or " "Connection, and no context was provided to locate " "a binding.") c_mapper = mapper is not None and _class_to_mapper(mapper) or None # manually bound? if self.__binds: if c_mapper: if c_mapper.base_mapper in self.__binds: return self.__binds[c_mapper.base_mapper] elif c_mapper.mapped_table in self.__binds: return self.__binds[c_mapper.mapped_table] if clause is not None: for t in sql_util.find_tables(clause, include_crud=True): if t in self.__binds: return self.__binds[t] if self.bind: return self.bind if isinstance(clause, sql.expression.ClauseElement) and clause.bind: return clause.bind if c_mapper and c_mapper.mapped_table.bind: return c_mapper.mapped_table.bind context = [] if mapper is not None: context.append('mapper %s' % c_mapper) if clause is not None: context.append('SQL expression') raise sa_exc.UnboundExecutionError( "Could not locate a bind configured on %s or this Session" % ( ', '.join(context))) def query(self, *entities, **kwargs): """Return a new ``Query`` object corresponding to this ``Session``.""" return self._query_cls(entities, self, **kwargs) @property @util.contextmanager def no_autoflush(self): """Return a context manager that disables autoflush. e.g.:: with session.no_autoflush: some_object = SomeClass() session.add(some_object) # won't autoflush some_object.related_thing = session.query(SomeRelated).first() Operations that proceed within the ``with:`` block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed. New in 0.7.6. """ autoflush = self.autoflush self.autoflush = False yield self self.autoflush = autoflush def _autoflush(self): if self.autoflush and not self._flushing: self.flush() def _finalize_loaded(self, states): for state, dict_ in states.items(): state.commit_all(dict_, self.identity_map) def refresh(self, instance, attribute_names=None, lockmode=None): """Expire and refresh the attributes on the given instance. A query will be issued to the database and all attributes will be refreshed with their current database value. Lazy-loaded relational attributes will remain lazily loaded, so that the instance-wide refresh operation will be followed immediately by the lazy load of that attribute. Eagerly-loaded relational attributes will eagerly load within the single refresh operation. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction - usage of :meth:`~Session.refresh` usually only makes sense if non-ORM SQL statement were emitted in the ongoing transaction, or if autocommit mode is turned on. :param attribute_names: optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed. :param lockmode: Passed to the :class:`~sqlalchemy.orm.query.Query` as used by :meth:`~sqlalchemy.orm.query.Query.with_lockmode`. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._expire_state(state, attribute_names) if self.query(_object_mapper(instance))._load_on_ident( state.key, refresh_state=state, lockmode=lockmode, only_load_props=attribute_names) is None: raise sa_exc.InvalidRequestError( "Could not refresh instance '%s'" % mapperutil.instance_str(instance)) def expire_all(self): """Expires all persistent instances within this Session. When any attributes on a persistent instance is next accessed, a query will be issued using the :class:`.Session` object's current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction. To expire individual objects and individual attributes on those objects, use :meth:`Session.expire`. The :class:`.Session` object's default behavior is to expire all state whenever the :meth:`Session.rollback` or :meth:`Session.commit` methods are called, so that new state can be loaded for the new transaction. For this reason, calling :meth:`Session.expire_all` should not be needed when autocommit is ``False``, assuming the transaction is isolated. """ for state in self.identity_map.all_states(): state.expire(state.dict, self.identity_map._modified) def expire(self, instance, attribute_names=None): """Expire the attributes on an instance. Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the :class:`.Session` object's current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction. To expire all objects in the :class:`.Session` simultaneously, use :meth:`Session.expire_all`. The :class:`.Session` object's default behavior is to expire all state whenever the :meth:`Session.rollback` or :meth:`Session.commit` methods are called, so that new state can be loaded for the new transaction. For this reason, calling :meth:`Session.expire` only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction. :param instance: The instance to be refreshed. :param attribute_names: optional list of string attribute names indicating a subset of attributes to be expired. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._expire_state(state, attribute_names) def _expire_state(self, state, attribute_names): self._validate_persistent(state) if attribute_names: state.expire_attributes(state.dict, attribute_names) else: # pre-fetch the full cascade since the expire is going to # remove associations cascaded = list(state.manager.mapper.cascade_iterator( 'refresh-expire', state)) self._conditional_expire(state) for o, m, st_, dct_ in cascaded: self._conditional_expire(st_) def _conditional_expire(self, state): """Expire a state if persistent, else expunge if pending""" if state.key: state.expire(state.dict, self.identity_map._modified) elif state in self._new: self._new.pop(state) state.detach() @util.deprecated("0.7", "The non-weak-referencing identity map " "feature is no longer needed.") def prune(self): """Remove unreferenced instances cached in the identity map. Note that this method is only meaningful if "weak_identity_map" is set to False. The default weak identity map is self-pruning. Removes any object in this Session's identity map that is not referenced in user code, modified, new or scheduled for deletion. Returns the number of objects pruned. """ return self.identity_map.prune() def expunge(self, instance): """Remove the `instance` from this ``Session``. This will free all internal references to the instance. Cascading will be applied according to the *expunge* cascade rule. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) if state.session_id is not self.hash_key: raise sa_exc.InvalidRequestError( "Instance %s is not present in this Session" % mapperutil.state_str(state)) cascaded = list(state.manager.mapper.cascade_iterator( 'expunge', state)) self._expunge_state(state) for o, m, st_, dct_ in cascaded: self._expunge_state(st_) def _expunge_state(self, state): if state in self._new: self._new.pop(state) state.detach() elif self.identity_map.contains_state(state): self.identity_map.discard(state) self._deleted.pop(state, None) state.detach() elif self.transaction: self.transaction._deleted.pop(state, None) def _register_newly_persistent(self, state): mapper = _state_mapper(state) # prevent against last minute dereferences of the object obj = state.obj() if obj is not None: instance_key = mapper._identity_key_from_state(state) if _none_set.issubset(instance_key[1]) and \ not mapper.allow_partial_pks or \ _none_set.issuperset(instance_key[1]): raise exc.FlushError( "Instance %s has a NULL identity key. If this is an " "auto-generated value, check that the database table " "allows generation of new primary key values, and that " "the mapped Column object is configured to expect these " "generated values. Ensure also that this flush() is " "not occurring at an inappropriate time, such as within " "a load() event." % mapperutil.state_str(state) ) if state.key is None: state.key = instance_key elif state.key != instance_key: # primary key switch. use discard() in case another # state has already replaced this one in the identity # map (see test/orm/test_naturalpks.py ReversePKsTest) self.identity_map.discard(state) state.key = instance_key self.identity_map.replace(state) state.commit_all(state.dict, self.identity_map) # remove from new last, might be the last strong ref if state in self._new: if self._enable_transaction_accounting and self.transaction: self.transaction._new[state] = True self._new.pop(state) def _remove_newly_deleted(self, state): if self._enable_transaction_accounting and self.transaction: self.transaction._deleted[state] = True self.identity_map.discard(state) self._deleted.pop(state, None) state.deleted = True def add(self, instance): """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()``. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) self._save_or_update_state(state) def add_all(self, instances): """Add the given collection of instances to this ``Session``.""" for instance in instances: self.add(instance) def _save_or_update_state(self, state): self._save_or_update_impl(state) mapper = _state_mapper(state) for o, m, st_, dct_ in mapper.cascade_iterator( 'save-update', state, halt_on=self._contains_state): self._save_or_update_impl(st_) def delete(self, instance): """Mark an instance as deleted. The database delete operation occurs upon ``flush()``. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) if state.key is None: raise sa_exc.InvalidRequestError( "Instance '%s' is not persisted" % mapperutil.state_str(state)) if state in self._deleted: return # ensure object is attached to allow the # cascade operation to load deferred attributes # and collections self._attach(state) # grab the cascades before adding the item to the deleted list # so that autoflush does not delete the item # the strong reference to the instance itself is significant here cascade_states = list(state.manager.mapper.cascade_iterator( 'delete', state)) self._deleted[state] = state.obj() self.identity_map.add(state) for o, m, st_, dct_ in cascade_states: self._delete_impl(st_) def merge(self, instance, load=True, **kw): """Copy the state an instance onto the persistent instance with the same identifier. If there is no persistent instance currently associated with the session, it will be loaded. Return the persistent instance. If the given instance is unsaved, save a copy of and return it as a newly persistent instance. The given instance does not become associated with the session. This operation cascades to associated instances if the association is mapped with ``cascade="merge"``. See :ref:`unitofwork_merging` for a detailed discussion of merging. """ if 'dont_load' in kw: load = not kw['dont_load'] util.warn_deprecated('dont_load=True has been renamed to ' 'load=False.') _recursive = {} if load: # flush current contents if we expect to load data self._autoflush() _object_mapper(instance) # verify mapped autoflush = self.autoflush try: self.autoflush = False return self._merge( attributes.instance_state(instance), attributes.instance_dict(instance), load=load, _recursive=_recursive) finally: self.autoflush = autoflush def _merge(self, state, state_dict, load=True, _recursive=None): mapper = _state_mapper(state) if state in _recursive: return _recursive[state] new_instance = False key = state.key if key is None: if not load: raise sa_exc.InvalidRequestError( "merge() with load=False option does not support " "objects transient (i.e. unpersisted) objects. flush() " "all changes on mapped instances before merging with " "load=False.") key = mapper._identity_key_from_state(state) if key in self.identity_map: merged = self.identity_map[key] elif not load: if state.modified: raise sa_exc.InvalidRequestError( "merge() with load=False option does not support " "objects marked as 'dirty'. flush() all changes on " "mapped instances before merging with load=False.") merged = mapper.class_manager.new_instance() merged_state = attributes.instance_state(merged) merged_state.key = key self._update_impl(merged_state) new_instance = True elif not _none_set.issubset(key[1]) or \ (mapper.allow_partial_pks and not _none_set.issuperset(key[1])): merged = self.query(mapper.class_).get(key[1]) else: merged = None if merged is None: merged = mapper.class_manager.new_instance() merged_state = attributes.instance_state(merged) merged_dict = attributes.instance_dict(merged) new_instance = True self._save_or_update_state(merged_state) else: merged_state = attributes.instance_state(merged) merged_dict = attributes.instance_dict(merged) _recursive[state] = merged # check that we didn't just pull the exact same # state out. if state is not merged_state: # version check if applicable if mapper.version_id_col is not None: existing_version = mapper._get_state_attr_by_column( state, state_dict, mapper.version_id_col, passive=attributes.PASSIVE_NO_INITIALIZE) merged_version = mapper._get_state_attr_by_column( merged_state, merged_dict, mapper.version_id_col, passive=attributes.PASSIVE_NO_INITIALIZE) if existing_version is not attributes.PASSIVE_NO_RESULT and \ merged_version is not attributes.PASSIVE_NO_RESULT and \ existing_version != merged_version: raise exc.StaleDataError( "Version id '%s' on merged state %s " "does not match existing version '%s'. " "Leave the version attribute unset when " "merging to update the most recent version." % ( existing_version, mapperutil.state_str(merged_state), merged_version )) merged_state.load_path = state.load_path merged_state.load_options = state.load_options for prop in mapper.iterate_properties: prop.merge(self, state, state_dict, merged_state, merged_dict, load, _recursive) if not load: # remove any history merged_state.commit_all(merged_dict, self.identity_map) if new_instance: merged_state.manager.dispatch.load(merged_state, None) return merged @classmethod def identity_key(cls, *args, **kwargs): return mapperutil.identity_key(*args, **kwargs) @classmethod def object_session(cls, instance): """Return the ``Session`` to which an object belongs.""" return object_session(instance) def _validate_persistent(self, state): if not self.identity_map.contains_state(state): raise sa_exc.InvalidRequestError( "Instance '%s' is not persistent within this Session" % mapperutil.state_str(state)) def _save_impl(self, state): if state.key is not None: raise sa_exc.InvalidRequestError( "Object '%s' already has an identity - it can't be registered " "as pending" % mapperutil.state_str(state)) self._attach(state) if state not in self._new: self._new[state] = state.obj() state.insert_order = len(self._new) def _update_impl(self, state): if (self.identity_map.contains_state(state) and state not in self._deleted): return if state.key is None: raise sa_exc.InvalidRequestError( "Instance '%s' is not persisted" % mapperutil.state_str(state)) if state.deleted: raise sa_exc.InvalidRequestError( "Instance '%s' has been deleted. Use the make_transient() " "function to send this object back to the transient state." % mapperutil.state_str(state) ) self._attach(state) self._deleted.pop(state, None) self.identity_map.add(state) def _save_or_update_impl(self, state): if state.key is None: self._save_impl(state) else: self._update_impl(state) def _delete_impl(self, state): if state in self._deleted: return if state.key is None: return self._attach(state) self._deleted[state] = state.obj() self.identity_map.add(state) def _attach(self, state): if state.key and \ state.key in self.identity_map and \ not self.identity_map.contains_state(state): raise sa_exc.InvalidRequestError("Can't attach instance " "%s; another instance with key %s is already " "present in this session." % (mapperutil.state_str(state), state.key)) if state.session_id and \ state.session_id is not self.hash_key and \ state.session_id in _sessions: raise sa_exc.InvalidRequestError( "Object '%s' is already attached to session '%s' " "(this is '%s')" % (mapperutil.state_str(state), state.session_id, self.hash_key)) if state.session_id != self.hash_key: state.session_id = self.hash_key if self.dispatch.after_attach: self.dispatch.after_attach(self, state.obj()) def __contains__(self, instance): """Return True if the instance is associated with this session. The instance may be pending or persistent within the Session for a result of True. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) return self._contains_state(state) def __iter__(self): """Iterate over all pending or persistent instances within this Session.""" return iter(list(self._new.values()) + self.identity_map.values()) def _contains_state(self, state): return state in self._new or self.identity_map.contains_state(state) def flush(self, objects=None): """Flush all the object changes to the database. Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session's unit of work dependency solver. Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database's transaction buffer. For ``autocommit`` Sessions with no active manual transaction, flush() will create a transaction on the fly that surrounds the entire set of operations int the flush. objects Optional; a list or tuple collection. Restricts the flush operation to only these objects, rather than all pending changes. Deprecated - this flag prevents the session from properly maintaining accounting among inter-object relations and can cause invalid results. """ if objects: util.warn_deprecated( "The 'objects' argument to session.flush() is deprecated; " "Please do not add objects to the session which should not " "yet be persisted.") if self._flushing: raise sa_exc.InvalidRequestError("Session is already flushing") if self._is_clean(): return try: self._flushing = True self._flush(objects) finally: self._flushing = False def _is_clean(self): return not self.identity_map.check_modified() and \ not self._deleted and \ not self._new def _flush(self, objects=None): dirty = self._dirty_states if not dirty and not self._deleted and not self._new: self.identity_map._modified.clear() return flush_context = UOWTransaction(self) if self.dispatch.before_flush: self.dispatch.before_flush(self, flush_context, objects) # re-establish "dirty states" in case the listeners # added dirty = self._dirty_states deleted = set(self._deleted) new = set(self._new) dirty = set(dirty).difference(deleted) # create the set of all objects we want to operate upon if objects: # specific list passed in objset = set() for o in objects: try: state = attributes.instance_state(o) except exc.NO_STATE: raise exc.UnmappedInstanceError(o) objset.add(state) else: objset = None # store objects whose fate has been decided processed = set() # put all saves/updates into the flush context. detect top-level # orphans and throw them into deleted. if objset: proc = new.union(dirty).intersection(objset).difference(deleted) else: proc = new.union(dirty).difference(deleted) for state in proc: is_orphan = _state_mapper(state)._is_orphan(state) and state.has_identity flush_context.register_object(state, isdelete=is_orphan) processed.add(state) # put all remaining deletes into the flush context. if objset: proc = deleted.intersection(objset).difference(processed) else: proc = deleted.difference(processed) for state in proc: flush_context.register_object(state, isdelete=True) if not flush_context.has_work: return flush_context.transaction = transaction = self.begin( subtransactions=True) try: flush_context.execute() self.dispatch.after_flush(self, flush_context) flush_context.finalize_flush_changes() # useful assertions: #if not objects: # assert not self.identity_map._modified #else: # assert self.identity_map._modified == \ # self.identity_map._modified.difference(objects) self.dispatch.after_flush_postexec(self, flush_context) transaction.commit() except: transaction.rollback(_capture_exception=True) raise def is_modified(self, instance, include_collections=True, passive=attributes.PASSIVE_OFF): """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, passive=True) .. note:: In SQLAlchemy 0.7 and earlier, the ``passive`` flag should **always** be explicitly set to ``True``. The current default value of :data:`.attributes.PASSIVE_OFF` for this flag is incorrect, in that it loads unloaded collections and attributes which by definition have no modified state, and furthermore trips off autoflush which then causes all subsequent, possibly modified attributes to lose their modified state. The default value of the flag will be changed in 0.8. 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 only if the attribute container has the ``active_history`` flag set to ``True``. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the ``active_history`` argument with :func:`.column_property`. :param instance: mapped instance to be tested for pending changes. :param include_collections: Indicates if multivalued collections should be included in the operation. Setting this to ``False`` is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush. :param passive: Indicates if unloaded attributes and collections should be loaded in the course of performing this test. If set to ``False``, or left at its default value of :data:`.PASSIVE_OFF`, unloaded attributes will be loaded. If set to ``True`` or :data:`.PASSIVE_NO_INITIALIZE`, unloaded collections and attributes will remain unloaded. As noted previously, the existence of this flag here is a bug, as unloaded attributes by definition have no changes, and the load operation also triggers an autoflush which then cancels out subsequent changes. This flag should **always be set to True**. In 0.8 the flag will be deprecated and the default set to ``True``. """ try: state = attributes.instance_state(instance) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) dict_ = state.dict if passive is True: passive = attributes.PASSIVE_NO_INITIALIZE elif passive is False: passive = attributes.PASSIVE_OFF for attr in state.manager.attributes: if \ ( not include_collections and hasattr(attr.impl, 'get_collection') ) or not hasattr(attr.impl, 'get_history'): continue (added, unchanged, deleted) = \ attr.impl.get_history(state, dict_, passive=passive) if added or deleted: return True return False @property def is_active(self): """True if this :class:`.Session` has an active transaction. This indicates if the :class:`.Session` is capable of emitting SQL, as from the :meth:`.Session.execute`, :meth:`.Session.query`, or :meth:`.Session.flush` methods. If False, it indicates that the innermost transaction has been rolled back, but enclosing :class:`.SessionTransaction` objects remain in the transactional stack, which also must be rolled back. This flag is generally only useful with a :class:`.Session` configured in its default mode of ``autocommit=False``. """ return self.transaction and self.transaction.is_active identity_map = None """A mapping of object identities to objects themselves. Iterating through ``Session.identity_map.values()`` provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session. See also: :func:`.identity_key` - operations involving identity keys. """ @property def _dirty_states(self): """The set of all persistent states considered dirty. This method returns all states that were modified including those that were possibly deleted. """ return self.identity_map._dirty_states() @property def dirty(self): """The set of all persistent instances considered dirty. E.g.:: some_mapped_object in session.dirty Instances are considered dirty when they were modified but not deleted. Note that this 'dirty' calculation is 'optimistic'; most attribute-setting or collection modification operations will mark an instance as 'dirty' and place it in this set, even if there is no net change to the attribute's value. At flush time, the value of each attribute is compared to its previously saved value, and if there's no net change, no SQL operation will occur (this is a more expensive operation so it's only done at flush time). To check if an instance has actionable net changes to its attributes, use the :meth:`.Session.is_modified` method. """ return util.IdentitySet( [state.obj() for state in self._dirty_states if state not in self._deleted]) @property def deleted(self): "The set of all instances marked as 'deleted' within this ``Session``" return util.IdentitySet(self._deleted.values()) @property def new(self): "The set of all instances marked as 'new' within this ``Session``." return util.IdentitySet(self._new.values()) _sessions = weakref.WeakValueDictionary() def make_transient(instance): """Make the given instance 'transient'. This will remove its association with any session and additionally will remove its "identity key", such that it's as though the object were newly constructed, except retaining its values. It also resets the "deleted" flag on the state if this object had been explicitly deleted by its session. Attributes which were "expired" or deferred at the instance level are reverted to undefined, and will not trigger any loads. """ state = attributes.instance_state(instance) s = _state_session(state) if s: s._expunge_state(state) # remove expired state and # deferred callables state.callables.clear() if state.key: del state.key if state.deleted: del state.deleted def object_session(instance): """Return the ``Session`` to which instance belongs. If the instance is not a mapped instance, an error is raised. """ try: return _state_session(attributes.instance_state(instance)) except exc.NO_STATE: raise exc.UnmappedInstanceError(instance) def _state_session(state): if state.session_id: try: return _sessions[state.session_id] except KeyError: pass return None _new_sessionid = util.counter()