Mini Shell
# engine/base.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
from __future__ import with_statement
import contextlib
import sys
from .interfaces import Connectable
from .interfaces import ExceptionContext
from .util import _distill_params
from .. import exc
from .. import interfaces
from .. import log
from .. import util
from ..sql import schema
from ..sql import util as sql_util
"""Defines :class:`_engine.Connection` and :class:`_engine.Engine`.
"""
class Connection(Connectable):
"""Provides high-level functionality for a wrapped DB-API connection.
Provides execution support for string-based SQL statements as well as
:class:`_expression.ClauseElement`, :class:`.Compiled` and
:class:`.DefaultGenerator`
objects. Provides a :meth:`begin` method to return :class:`.Transaction`
objects.
The Connection object is **not** thread-safe. While a Connection can be
shared among threads using properly synchronized access, it is still
possible that the underlying DBAPI connection may not support shared
access between threads. Check the DBAPI documentation for details.
The Connection object represents a single DBAPI connection checked out
from the connection pool. In this state, the connection pool has no affect
upon the connection, including its expiration or timeout state. For the
connection pool to properly manage connections, connections should be
returned to the connection pool (i.e. ``connection.close()``) whenever the
connection is not in use.
.. index::
single: thread safety; Connection
"""
schema_for_object = schema._schema_getter(None)
"""Return the ".schema" attribute for an object.
Used for :class:`_schema.Table`, :class:`.Sequence` and similar objects,
and takes into account
the :paramref:`.Connection.execution_options.schema_translate_map`
parameter.
.. versionadded:: 1.1
.. seealso::
:ref:`schema_translating`
"""
def __init__(
self,
engine,
connection=None,
close_with_result=False,
_branch_from=None,
_execution_options=None,
_dispatch=None,
_has_events=None,
):
"""Construct a new Connection.
The constructor here is not public and is only called only by an
:class:`_engine.Engine`. See :meth:`_engine.Engine.connect` and
:meth:`_engine.Engine.contextual_connect` methods.
"""
self.engine = engine
self.dialect = engine.dialect
self.__branch_from = _branch_from
self.__branch = _branch_from is not None
if _branch_from:
self.__connection = connection
self._execution_options = _execution_options
self._echo = _branch_from._echo
self.should_close_with_result = False
self.dispatch = _dispatch
self._has_events = _branch_from._has_events
self.schema_for_object = _branch_from.schema_for_object
else:
self.__connection = (
connection
if connection is not None
else engine.raw_connection()
)
self.__transaction = None
self.__savepoint_seq = 0
self.should_close_with_result = close_with_result
self.__invalid = False
self.__can_reconnect = True
self._echo = self.engine._should_log_info()
if _has_events is None:
# if _has_events is sent explicitly as False,
# then don't join the dispatch of the engine; we don't
# want to handle any of the engine's events in that case.
self.dispatch = self.dispatch._join(engine.dispatch)
self._has_events = _has_events or (
_has_events is None and engine._has_events
)
assert not _execution_options
self._execution_options = engine._execution_options
if self._has_events or self.engine._has_events:
self.dispatch.engine_connect(self, self.__branch)
def _branch(self):
"""Return a new Connection which references this Connection's
engine and connection; but does not have close_with_result enabled,
and also whose close() method does nothing.
The Core uses this very sparingly, only in the case of
custom SQL default functions that are to be INSERTed as the
primary key of a row where we need to get the value back, so we have
to invoke it distinctly - this is a very uncommon case.
Userland code accesses _branch() when the connect() or
contextual_connect() methods are called. The branched connection
acts as much as possible like the parent, except that it stays
connected when a close() event occurs.
"""
if self.__branch_from:
return self.__branch_from._branch()
else:
return self.engine._connection_cls(
self.engine,
self.__connection,
_branch_from=self,
_execution_options=self._execution_options,
_has_events=self._has_events,
_dispatch=self.dispatch,
)
@property
def _root(self):
"""Return the 'root' connection.
Returns 'self' if this connection is not a branch, else
returns the root connection from which we ultimately branched.
"""
if self.__branch_from:
return self.__branch_from
else:
return self
def _clone(self):
"""Create a shallow copy of this Connection."""
c = self.__class__.__new__(self.__class__)
c.__dict__ = self.__dict__.copy()
return c
def __enter__(self):
return self
def __exit__(self, type_, value, traceback):
self.close()
def execution_options(self, **opt):
r""" Set non-SQL options for the connection which take effect
during execution.
The method returns a copy of this :class:`_engine.Connection`
which references
the same underlying DBAPI connection, but also defines the given
execution options which will take effect for a call to
:meth:`execute`. As the new :class:`_engine.Connection`
references the same
underlying resource, it's usually a good idea to ensure that the copies
will be discarded immediately, which is implicit if used as in::
result = connection.execution_options(stream_results=True).\
execute(stmt)
Note that any key/value can be passed to
:meth:`_engine.Connection.execution_options`,
and it will be stored in the
``_execution_options`` dictionary of the :class:`_engine.Connection`.
It
is suitable for usage by end-user schemes to communicate with
event listeners, for example.
The keywords that are currently recognized by SQLAlchemy itself
include all those listed under :meth:`.Executable.execution_options`,
as well as others that are specific to :class:`_engine.Connection`.
:param autocommit: Available on: Connection, statement.
When True, a COMMIT will be invoked after execution
when executed in 'autocommit' mode, i.e. when an explicit
transaction is not begun on the connection. Note that this
is **library level, not DBAPI level autocommit**. The DBAPI
connection will remain in a real transaction unless the
"AUTOCOMMIT" isolation level is used.
.. deprecated:: 1.4 The library-level "autocommit" feature is being
removed in favor of database driver "autocommit" which is
now widely available. See the section :ref:`dbapi_autocommit`.
:param compiled_cache: Available on: Connection.
A dictionary where :class:`.Compiled` objects
will be cached when the :class:`_engine.Connection`
compiles a clause
expression into a :class:`.Compiled` object.
It is the user's responsibility to
manage the size of this dictionary, which will have keys
corresponding to the dialect, clause element, the column
names within the VALUES or SET clause of an INSERT or UPDATE,
as well as the "batch" mode for an INSERT or UPDATE statement.
The format of this dictionary is not guaranteed to stay the
same in future releases.
Note that the ORM makes use of its own "compiled" caches for
some operations, including flush operations. The caching
used by the ORM internally supersedes a cache dictionary
specified here.
:param isolation_level: Available on: :class:`_engine.Connection`.
Set the transaction isolation level for the lifespan of this
:class:`_engine.Connection` object.
Valid values include those string
values accepted by the :paramref:`_sa.create_engine.isolation_level`
parameter passed to :func:`_sa.create_engine`. These levels are
semi-database specific; see individual dialect documentation for
valid levels.
The isolation level option applies the isolation level by emitting
statements on the DBAPI connection, and **necessarily affects the
original Connection object overall**, not just the copy that is
returned by the call to :meth:`_engine.Connection.execution_options`
method. The isolation level will remain at the given setting until
the DBAPI connection itself is returned to the connection pool, i.e.
the :meth:`_engine.Connection.close` method on the original
:class:`_engine.Connection` is called,
where an event handler will emit
additional statements on the DBAPI connection in order to revert the
isolation level change.
.. warning:: The ``isolation_level`` execution option should
**not** be used when a transaction is already established, that
is, the :meth:`_engine.Connection.begin`
method or similar has been
called. A database cannot change the isolation level on a
transaction in progress, and different DBAPIs and/or
SQLAlchemy dialects may implicitly roll back or commit
the transaction, or not affect the connection at all.
.. note:: The ``isolation_level`` execution option is implicitly
reset if the :class:`_engine.Connection` is invalidated, e.g. via
the :meth:`_engine.Connection.invalidate` method, or if a
disconnection error occurs. The new connection produced after
the invalidation will not have the isolation level re-applied
to it automatically.
.. seealso::
:paramref:`_sa.create_engine.isolation_level`
- set per :class:`_engine.Engine` isolation level
:meth:`_engine.Connection.get_isolation_level`
- view current level
:ref:`SQLite Transaction Isolation <sqlite_isolation_level>`
:ref:`PostgreSQL Transaction Isolation <postgresql_isolation_level>`
:ref:`MySQL Transaction Isolation <mysql_isolation_level>`
:ref:`SQL Server Transaction Isolation <mssql_isolation_level>`
:ref:`session_transaction_isolation` - for the ORM
:param no_parameters: When ``True``, if the final parameter
list or dictionary is totally empty, will invoke the
statement on the cursor as ``cursor.execute(statement)``,
not passing the parameter collection at all.
Some DBAPIs such as psycopg2 and mysql-python consider
percent signs as significant only when parameters are
present; this option allows code to generate SQL
containing percent signs (and possibly other characters)
that is neutral regarding whether it's executed by the DBAPI
or piped into a script that's later invoked by
command line tools.
:param stream_results: Available on: Connection, statement.
Indicate to the dialect that results should be
"streamed" and not pre-buffered, if possible. This is a limitation
of many DBAPIs. The flag is currently understood only by the
psycopg2, mysqldb and pymysql dialects.
:param schema_translate_map: Available on: Connection, Engine.
A dictionary mapping schema names to schema names, that will be
applied to the :paramref:`_schema.Table.schema` element of each
:class:`_schema.Table`
encountered when SQL or DDL expression elements
are compiled into strings; the resulting schema name will be
converted based on presence in the map of the original name.
.. versionadded:: 1.1
.. seealso::
:ref:`schema_translating`
.. seealso::
:meth:`_engine.Engine.execution_options`
:meth:`.Executable.execution_options`
:meth:`_engine.Connection.get_execution_options`
""" # noqa
c = self._clone()
c._execution_options = c._execution_options.union(opt)
if self._has_events or self.engine._has_events:
self.dispatch.set_connection_execution_options(c, opt)
self.dialect.set_connection_execution_options(c, opt)
return c
def get_execution_options(self):
"""Get the non-SQL options which will take effect during execution.
.. versionadded:: 1.3
.. seealso::
:meth:`_engine.Connection.execution_options`
"""
return self._execution_options
@property
def closed(self):
"""Return True if this connection is closed."""
return (
"_Connection__connection" not in self.__dict__
and not self.__can_reconnect
)
@property
def invalidated(self):
"""Return True if this connection was invalidated."""
return self._root.__invalid
@property
def connection(self):
"""The underlying DB-API connection managed by this Connection.
.. seealso::
:ref:`dbapi_connections`
"""
try:
return self.__connection
except AttributeError:
# escape "except AttributeError" before revalidating
# to prevent misleading stacktraces in Py3K
pass
try:
return self._revalidate_connection()
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
def get_isolation_level(self):
"""Return the current isolation level assigned to this
:class:`_engine.Connection`.
This will typically be the default isolation level as determined
by the dialect, unless if the
:paramref:`.Connection.execution_options.isolation_level`
feature has been used to alter the isolation level on a
per-:class:`_engine.Connection` basis.
This attribute will typically perform a live SQL operation in order
to procure the current isolation level, so the value returned is the
actual level on the underlying DBAPI connection regardless of how
this state was set. Compare to the
:attr:`_engine.Connection.default_isolation_level` accessor
which returns the dialect-level setting without performing a SQL
query.
.. versionadded:: 0.9.9
.. seealso::
:attr:`_engine.Connection.default_isolation_level`
- view default level
:paramref:`_sa.create_engine.isolation_level`
- set per :class:`_engine.Engine` isolation level
:paramref:`.Connection.execution_options.isolation_level`
- set per :class:`_engine.Connection` isolation level
"""
try:
return self.dialect.get_isolation_level(self.connection)
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
@property
def default_isolation_level(self):
"""The default isolation level assigned to this
:class:`_engine.Connection`.
This is the isolation level setting that the
:class:`_engine.Connection`
has when first procured via the :meth:`_engine.Engine.connect` method.
This level stays in place until the
:paramref:`.Connection.execution_options.isolation_level` is used
to change the setting on a per-:class:`_engine.Connection` basis.
Unlike :meth:`_engine.Connection.get_isolation_level`,
this attribute is set
ahead of time from the first connection procured by the dialect,
so SQL query is not invoked when this accessor is called.
.. versionadded:: 0.9.9
.. seealso::
:meth:`_engine.Connection.get_isolation_level`
- view current level
:paramref:`_sa.create_engine.isolation_level`
- set per :class:`_engine.Engine` isolation level
:paramref:`.Connection.execution_options.isolation_level`
- set per :class:`_engine.Connection` isolation level
"""
return self.dialect.default_isolation_level
def _revalidate_connection(self):
if self.__branch_from:
return self.__branch_from._revalidate_connection()
if self.__can_reconnect and self.__invalid:
if self.__transaction is not None:
raise exc.InvalidRequestError(
"Can't reconnect until invalid "
"transaction is rolled back"
)
self.__connection = self.engine.raw_connection(_connection=self)
self.__invalid = False
return self.__connection
raise exc.ResourceClosedError("This Connection is closed")
@property
def _connection_is_valid(self):
# use getattr() for is_valid to support exceptions raised in
# dialect initializer, where the connection is not wrapped in
# _ConnectionFairy
return getattr(self.__connection, "is_valid", False)
@property
def _still_open_and_connection_is_valid(self):
return (
not self.closed
and not self.invalidated
and getattr(self.__connection, "is_valid", False)
)
@property
def info(self):
"""Info dictionary associated with the underlying DBAPI connection
referred to by this :class:`_engine.Connection`, allowing user-defined
data to be associated with the connection.
The data here will follow along with the DBAPI connection including
after it is returned to the connection pool and used again
in subsequent instances of :class:`_engine.Connection`.
"""
return self.connection.info
def connect(self):
"""Returns a branched version of this :class:`_engine.Connection`.
The :meth:`_engine.Connection.close` method on the returned
:class:`_engine.Connection` can be called and this
:class:`_engine.Connection` will remain open.
This method provides usage symmetry with
:meth:`_engine.Engine.connect`, including for usage
with context managers.
"""
return self._branch()
def _contextual_connect(self, **kwargs):
return self._branch()
def invalidate(self, exception=None):
"""Invalidate the underlying DBAPI connection associated with
this :class:`_engine.Connection`.
The underlying DBAPI connection is literally closed (if
possible), and is discarded. Its source connection pool will
typically lazily create a new connection to replace it.
Upon the next use (where "use" typically means using the
:meth:`_engine.Connection.execute` method or similar),
this :class:`_engine.Connection` will attempt to
procure a new DBAPI connection using the services of the
:class:`_pool.Pool` as a source of connectivity (e.g.
a "reconnection").
If a transaction was in progress (e.g. the
:meth:`_engine.Connection.begin` method has been called) when
:meth:`_engine.Connection.invalidate` method is called, at the DBAPI
level all state associated with this transaction is lost, as
the DBAPI connection is closed. The :class:`_engine.Connection`
will not allow a reconnection to proceed until the
:class:`.Transaction` object is ended, by calling the
:meth:`.Transaction.rollback` method; until that point, any attempt at
continuing to use the :class:`_engine.Connection` will raise an
:class:`~sqlalchemy.exc.InvalidRequestError`.
This is to prevent applications from accidentally
continuing an ongoing transactional operations despite the
fact that the transaction has been lost due to an
invalidation.
The :meth:`_engine.Connection.invalidate` method,
just like auto-invalidation,
will at the connection pool level invoke the
:meth:`_events.PoolEvents.invalidate` event.
.. seealso::
:ref:`pool_connection_invalidation`
"""
if self.invalidated:
return
if self.closed:
raise exc.ResourceClosedError("This Connection is closed")
if self._root._connection_is_valid:
self._root.__connection.invalidate(exception)
del self._root.__connection
self._root.__invalid = True
def detach(self):
"""Detach the underlying DB-API connection from its connection pool.
E.g.::
with engine.connect() as conn:
conn.detach()
conn.execute("SET search_path TO schema1, schema2")
# work with connection
# connection is fully closed (since we used "with:", can
# also call .close())
This :class:`_engine.Connection` instance will remain usable.
When closed
(or exited from a context manager context as above),
the DB-API connection will be literally closed and not
returned to its originating pool.
This method can be used to insulate the rest of an application
from a modified state on a connection (such as a transaction
isolation level or similar).
"""
self.__connection.detach()
def begin(self):
"""Begin a transaction and return a transaction handle.
The returned object is an instance of :class:`.Transaction`.
This object represents the "scope" of the transaction,
which completes when either the :meth:`.Transaction.rollback`
or :meth:`.Transaction.commit` method is called.
Nested calls to :meth:`.begin` on the same :class:`_engine.Connection`
will return new :class:`.Transaction` objects that represent
an emulated transaction within the scope of the enclosing
transaction, that is::
trans = conn.begin() # outermost transaction
trans2 = conn.begin() # "nested"
trans2.commit() # does nothing
trans.commit() # actually commits
Calls to :meth:`.Transaction.commit` only have an effect
when invoked via the outermost :class:`.Transaction` object, though the
:meth:`.Transaction.rollback` method of any of the
:class:`.Transaction` objects will roll back the
transaction.
.. seealso::
:meth:`_engine.Connection.begin_nested` - use a SAVEPOINT
:meth:`_engine.Connection.begin_twophase` -
use a two phase /XID transaction
:meth:`_engine.Engine.begin` - context manager available from
:class:`_engine.Engine`
"""
if self.__branch_from:
return self.__branch_from.begin()
if self.__transaction is None:
self.__transaction = RootTransaction(self)
return self.__transaction
else:
return Transaction(self, self.__transaction)
def begin_nested(self):
"""Begin a nested transaction and return a transaction handle.
The returned object is an instance of :class:`.NestedTransaction`.
Nested transactions require SAVEPOINT support in the
underlying database. Any transaction in the hierarchy may
``commit`` and ``rollback``, however the outermost transaction
still controls the overall ``commit`` or ``rollback`` of the
transaction of a whole.
.. seealso::
:meth:`_engine.Connection.begin`
:meth:`_engine.Connection.begin_twophase`
"""
if self.__branch_from:
return self.__branch_from.begin_nested()
if self.__transaction is None:
self.__transaction = RootTransaction(self)
else:
self.__transaction = NestedTransaction(self, self.__transaction)
return self.__transaction
def begin_twophase(self, xid=None):
"""Begin a two-phase or XA transaction and return a transaction
handle.
The returned object is an instance of :class:`.TwoPhaseTransaction`,
which in addition to the methods provided by
:class:`.Transaction`, also provides a
:meth:`~.TwoPhaseTransaction.prepare` method.
:param xid: the two phase transaction id. If not supplied, a
random id will be generated.
.. seealso::
:meth:`_engine.Connection.begin`
:meth:`_engine.Connection.begin_twophase`
"""
if self.__branch_from:
return self.__branch_from.begin_twophase(xid=xid)
if self.__transaction is not None:
raise exc.InvalidRequestError(
"Cannot start a two phase transaction when a transaction "
"is already in progress."
)
if xid is None:
xid = self.engine.dialect.create_xid()
self.__transaction = TwoPhaseTransaction(self, xid)
return self.__transaction
def recover_twophase(self):
return self.engine.dialect.do_recover_twophase(self)
def rollback_prepared(self, xid, recover=False):
self.engine.dialect.do_rollback_twophase(self, xid, recover=recover)
def commit_prepared(self, xid, recover=False):
self.engine.dialect.do_commit_twophase(self, xid, recover=recover)
def in_transaction(self):
"""Return True if a transaction is in progress."""
return self._root.__transaction is not None
def _begin_impl(self, transaction):
assert not self.__branch_from
if self._echo:
self.engine.logger.info("BEGIN (implicit)")
if self._has_events or self.engine._has_events:
self.dispatch.begin(self)
try:
self.engine.dialect.do_begin(self.connection)
if self.connection._reset_agent is None:
self.connection._reset_agent = transaction
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
def _rollback_impl(self):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.rollback(self)
if self._still_open_and_connection_is_valid:
if self._echo:
self.engine.logger.info("ROLLBACK")
try:
self.engine.dialect.do_rollback(self.connection)
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
finally:
if (
not self.__invalid
and self.connection._reset_agent is self.__transaction
):
self.connection._reset_agent = None
self.__transaction = None
else:
self.__transaction = None
def _commit_impl(self, autocommit=False):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.commit(self)
if self._echo:
self.engine.logger.info("COMMIT")
try:
self.engine.dialect.do_commit(self.connection)
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
finally:
if (
not self.__invalid
and self.connection._reset_agent is self.__transaction
):
self.connection._reset_agent = None
self.__transaction = None
def _savepoint_impl(self, name=None):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.savepoint(self, name)
if name is None:
self.__savepoint_seq += 1
name = "sa_savepoint_%s" % self.__savepoint_seq
if self._still_open_and_connection_is_valid:
self.engine.dialect.do_savepoint(self, name)
return name
def _discard_transaction(self, trans):
if trans is self.__transaction:
if trans._parent is trans:
self.__transaction = None
else:
self.__transaction = trans._parent
if self._still_open_and_connection_is_valid:
if self.__connection._reset_agent is trans:
self.__connection._reset_agent = None
def _rollback_to_savepoint_impl(self, name, context):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.rollback_savepoint(self, name, context)
if self._still_open_and_connection_is_valid:
self.engine.dialect.do_rollback_to_savepoint(self, name)
self.__transaction = context
def _release_savepoint_impl(self, name, context):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.release_savepoint(self, name, context)
if self._still_open_and_connection_is_valid:
self.engine.dialect.do_release_savepoint(self, name)
self.__transaction = context
def _begin_twophase_impl(self, transaction):
assert not self.__branch_from
if self._echo:
self.engine.logger.info("BEGIN TWOPHASE (implicit)")
if self._has_events or self.engine._has_events:
self.dispatch.begin_twophase(self, transaction.xid)
if self._still_open_and_connection_is_valid:
self.engine.dialect.do_begin_twophase(self, transaction.xid)
if self.connection._reset_agent is None:
self.connection._reset_agent = transaction
def _prepare_twophase_impl(self, xid):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.prepare_twophase(self, xid)
if self._still_open_and_connection_is_valid:
assert isinstance(self.__transaction, TwoPhaseTransaction)
self.engine.dialect.do_prepare_twophase(self, xid)
def _rollback_twophase_impl(self, xid, is_prepared):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.rollback_twophase(self, xid, is_prepared)
if self._still_open_and_connection_is_valid:
assert isinstance(self.__transaction, TwoPhaseTransaction)
try:
self.engine.dialect.do_rollback_twophase(
self, xid, is_prepared
)
finally:
if self.connection._reset_agent is self.__transaction:
self.connection._reset_agent = None
self.__transaction = None
else:
self.__transaction = None
def _commit_twophase_impl(self, xid, is_prepared):
assert not self.__branch_from
if self._has_events or self.engine._has_events:
self.dispatch.commit_twophase(self, xid, is_prepared)
if self._still_open_and_connection_is_valid:
assert isinstance(self.__transaction, TwoPhaseTransaction)
try:
self.engine.dialect.do_commit_twophase(self, xid, is_prepared)
finally:
if self.connection._reset_agent is self.__transaction:
self.connection._reset_agent = None
self.__transaction = None
else:
self.__transaction = None
def _autorollback(self):
if not self._root.in_transaction():
self._root._rollback_impl()
def close(self):
"""Close this :class:`_engine.Connection`.
This results in a release of the underlying database
resources, that is, the DBAPI connection referenced
internally. The DBAPI connection is typically restored
back to the connection-holding :class:`_pool.Pool` referenced
by the :class:`_engine.Engine` that produced this
:class:`_engine.Connection`. Any transactional state present on
the DBAPI connection is also unconditionally released via
the DBAPI connection's ``rollback()`` method, regardless
of any :class:`.Transaction` object that may be
outstanding with regards to this :class:`_engine.Connection`.
After :meth:`_engine.Connection.close` is called, the
:class:`_engine.Connection` is permanently in a closed state,
and will allow no further operations.
"""
if self.__branch_from:
try:
del self.__connection
except AttributeError:
pass
finally:
self.__can_reconnect = False
return
try:
conn = self.__connection
except AttributeError:
pass
else:
conn.close()
if conn._reset_agent is self.__transaction:
conn._reset_agent = None
# the close() process can end up invalidating us,
# as the pool will call our transaction as the "reset_agent"
# for rollback(), which can then cause an invalidation
if not self.__invalid:
del self.__connection
self.__can_reconnect = False
self.__transaction = None
def scalar(self, object_, *multiparams, **params):
"""Executes and returns the first column of the first row.
The underlying result/cursor is closed after execution.
"""
return self.execute(object_, *multiparams, **params).scalar()
def execute(self, object_, *multiparams, **params):
r"""Executes a SQL statement construct and returns a
:class:`_engine.ResultProxy`.
:param object: The statement to be executed. May be
one of:
* a plain string
* any :class:`_expression.ClauseElement` construct that is also
a subclass of :class:`.Executable`, such as a
:func:`_expression.select` construct
* a :class:`.FunctionElement`, such as that generated
by :data:`.func`, will be automatically wrapped in
a SELECT statement, which is then executed.
* a :class:`.DDLElement` object
* a :class:`.DefaultGenerator` object
* a :class:`.Compiled` object
:param \*multiparams/\**params: represent bound parameter
values to be used in the execution. Typically,
the format is either a collection of one or more
dictionaries passed to \*multiparams::
conn.execute(
table.insert(),
{"id":1, "value":"v1"},
{"id":2, "value":"v2"}
)
...or individual key/values interpreted by \**params::
conn.execute(
table.insert(), id=1, value="v1"
)
In the case that a plain SQL string is passed, and the underlying
DBAPI accepts positional bind parameters, a collection of tuples
or individual values in \*multiparams may be passed::
conn.execute(
"INSERT INTO table (id, value) VALUES (?, ?)",
(1, "v1"), (2, "v2")
)
conn.execute(
"INSERT INTO table (id, value) VALUES (?, ?)",
1, "v1"
)
Note above, the usage of a question mark "?" or other
symbol is contingent upon the "paramstyle" accepted by the DBAPI
in use, which may be any of "qmark", "named", "pyformat", "format",
"numeric". See `pep-249 <http://www.python.org/dev/peps/pep-0249/>`_
for details on paramstyle.
To execute a textual SQL statement which uses bound parameters in a
DBAPI-agnostic way, use the :func:`_expression.text` construct.
"""
if isinstance(object_, util.string_types[0]):
return self._execute_text(object_, multiparams, params)
try:
meth = object_._execute_on_connection
except AttributeError as err:
util.raise_(
exc.ObjectNotExecutableError(object_), replace_context=err
)
else:
return meth(self, multiparams, params)
def _execute_function(self, func, multiparams, params):
"""Execute a sql.FunctionElement object."""
return self._execute_clauseelement(func.select(), multiparams, params)
def _execute_default(self, default, multiparams, params):
"""Execute a schema.ColumnDefault object."""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_execute:
default, multiparams, params = fn(
self, default, multiparams, params
)
try:
try:
conn = self.__connection
except AttributeError:
# escape "except AttributeError" before revalidating
# to prevent misleading stacktraces in Py3K
conn = None
if conn is None:
conn = self._revalidate_connection()
dialect = self.dialect
ctx = dialect.execution_ctx_cls._init_default(dialect, self, conn)
except BaseException as e:
self._handle_dbapi_exception(e, None, None, None, None)
ret = ctx._exec_default(None, default, None)
if self.should_close_with_result:
self.close()
if self._has_events or self.engine._has_events:
self.dispatch.after_execute(
self, default, multiparams, params, ret
)
return ret
def _execute_ddl(self, ddl, multiparams, params):
"""Execute a schema.DDL object."""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_execute:
ddl, multiparams, params = fn(self, ddl, multiparams, params)
dialect = self.dialect
compiled = ddl.compile(
dialect=dialect,
schema_translate_map=self.schema_for_object
if not self.schema_for_object.is_default
else None,
)
ret = self._execute_context(
dialect,
dialect.execution_ctx_cls._init_ddl,
compiled,
None,
compiled,
)
if self._has_events or self.engine._has_events:
self.dispatch.after_execute(self, ddl, multiparams, params, ret)
return ret
def _execute_clauseelement(self, elem, multiparams, params):
"""Execute a sql.ClauseElement object."""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_execute:
elem, multiparams, params = fn(self, elem, multiparams, params)
distilled_params = _distill_params(multiparams, params)
if distilled_params:
# ensure we don't retain a link to the view object for keys()
# which links to the values, which we don't want to cache
keys = list(distilled_params[0].keys())
else:
keys = []
dialect = self.dialect
if "compiled_cache" in self._execution_options:
key = (
dialect,
elem,
tuple(sorted(keys)),
self.schema_for_object.hash_key,
len(distilled_params) > 1,
)
compiled_sql = self._execution_options["compiled_cache"].get(key)
if compiled_sql is None:
compiled_sql = elem.compile(
dialect=dialect,
column_keys=keys,
inline=len(distilled_params) > 1,
schema_translate_map=self.schema_for_object
if not self.schema_for_object.is_default
else None,
)
self._execution_options["compiled_cache"][key] = compiled_sql
else:
compiled_sql = elem.compile(
dialect=dialect,
column_keys=keys,
inline=len(distilled_params) > 1,
schema_translate_map=self.schema_for_object
if not self.schema_for_object.is_default
else None,
)
ret = self._execute_context(
dialect,
dialect.execution_ctx_cls._init_compiled,
compiled_sql,
distilled_params,
compiled_sql,
distilled_params,
)
if self._has_events or self.engine._has_events:
self.dispatch.after_execute(self, elem, multiparams, params, ret)
return ret
def _execute_compiled(self, compiled, multiparams, params):
"""Execute a sql.Compiled object."""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_execute:
compiled, multiparams, params = fn(
self, compiled, multiparams, params
)
dialect = self.dialect
parameters = _distill_params(multiparams, params)
ret = self._execute_context(
dialect,
dialect.execution_ctx_cls._init_compiled,
compiled,
parameters,
compiled,
parameters,
)
if self._has_events or self.engine._has_events:
self.dispatch.after_execute(
self, compiled, multiparams, params, ret
)
return ret
def _execute_text(self, statement, multiparams, params):
"""Execute a string SQL statement."""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_execute:
statement, multiparams, params = fn(
self, statement, multiparams, params
)
dialect = self.dialect
parameters = _distill_params(multiparams, params)
ret = self._execute_context(
dialect,
dialect.execution_ctx_cls._init_statement,
statement,
parameters,
statement,
parameters,
)
if self._has_events or self.engine._has_events:
self.dispatch.after_execute(
self, statement, multiparams, params, ret
)
return ret
def _execute_context(
self, dialect, constructor, statement, parameters, *args
):
"""Create an :class:`.ExecutionContext` and execute, returning
a :class:`_engine.ResultProxy`.
"""
try:
try:
conn = self.__connection
except AttributeError:
# escape "except AttributeError" before revalidating
# to prevent misleading stacktraces in Py3K
conn = None
if conn is None:
conn = self._revalidate_connection()
context = constructor(dialect, self, conn, *args)
except BaseException as e:
self._handle_dbapi_exception(
e, util.text_type(statement), parameters, None, None
)
if context.compiled:
context.pre_exec()
cursor, statement, parameters = (
context.cursor,
context.statement,
context.parameters,
)
if not context.executemany:
parameters = parameters[0]
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_cursor_execute:
statement, parameters = fn(
self,
cursor,
statement,
parameters,
context,
context.executemany,
)
if self._echo:
self.engine.logger.info(statement)
if not self.engine.hide_parameters:
self.engine.logger.info(
"%r",
sql_util._repr_params(
parameters, batches=10, ismulti=context.executemany
),
)
else:
self.engine.logger.info(
"[SQL parameters hidden due to hide_parameters=True]"
)
evt_handled = False
try:
if context.executemany:
if self.dialect._has_events:
for fn in self.dialect.dispatch.do_executemany:
if fn(cursor, statement, parameters, context):
evt_handled = True
break
if not evt_handled:
self.dialect.do_executemany(
cursor, statement, parameters, context
)
elif not parameters and context.no_parameters:
if self.dialect._has_events:
for fn in self.dialect.dispatch.do_execute_no_params:
if fn(cursor, statement, context):
evt_handled = True
break
if not evt_handled:
self.dialect.do_execute_no_params(
cursor, statement, context
)
else:
if self.dialect._has_events:
for fn in self.dialect.dispatch.do_execute:
if fn(cursor, statement, parameters, context):
evt_handled = True
break
if not evt_handled:
self.dialect.do_execute(
cursor, statement, parameters, context
)
if self._has_events or self.engine._has_events:
self.dispatch.after_cursor_execute(
self,
cursor,
statement,
parameters,
context,
context.executemany,
)
if context.compiled:
context.post_exec()
if context.is_crud or context.is_text:
result = context._setup_crud_result_proxy()
else:
result = context.get_result_proxy()
if result._metadata is None:
result._soft_close()
if context.should_autocommit and self._root.__transaction is None:
self._root._commit_impl(autocommit=True)
# for "connectionless" execution, we have to close this
# Connection after the statement is complete.
if self.should_close_with_result:
# ResultProxy already exhausted rows / has no rows.
# close us now
if result._soft_closed:
self.close()
else:
# ResultProxy will close this Connection when no more
# rows to fetch.
result._autoclose_connection = True
except BaseException as e:
self._handle_dbapi_exception(
e, statement, parameters, cursor, context
)
return result
def _cursor_execute(self, cursor, statement, parameters, context=None):
"""Execute a statement + params on the given cursor.
Adds appropriate logging and exception handling.
This method is used by DefaultDialect for special-case
executions, such as for sequences and column defaults.
The path of statement execution in the majority of cases
terminates at _execute_context().
"""
if self._has_events or self.engine._has_events:
for fn in self.dispatch.before_cursor_execute:
statement, parameters = fn(
self, cursor, statement, parameters, context, False
)
if self._echo:
self.engine.logger.info(statement)
self.engine.logger.info("%r", parameters)
try:
for fn in (
()
if not self.dialect._has_events
else self.dialect.dispatch.do_execute
):
if fn(cursor, statement, parameters, context):
break
else:
self.dialect.do_execute(cursor, statement, parameters, context)
except BaseException as e:
self._handle_dbapi_exception(
e, statement, parameters, cursor, context
)
if self._has_events or self.engine._has_events:
self.dispatch.after_cursor_execute(
self, cursor, statement, parameters, context, False
)
def _safe_close_cursor(self, cursor):
"""Close the given cursor, catching exceptions
and turning into log warnings.
"""
try:
cursor.close()
except Exception:
# log the error through the connection pool's logger.
self.engine.pool.logger.error(
"Error closing cursor", exc_info=True
)
_reentrant_error = False
_is_disconnect = False
def _handle_dbapi_exception(
self, e, statement, parameters, cursor, context
):
exc_info = sys.exc_info()
if context and context.exception is None:
context.exception = e
is_exit_exception = not isinstance(e, Exception)
if not self._is_disconnect:
self._is_disconnect = (
isinstance(e, self.dialect.dbapi.Error)
and not self.closed
and self.dialect.is_disconnect(
e,
self.__connection if not self.invalidated else None,
cursor,
)
) or (is_exit_exception and not self.closed)
if context:
context.is_disconnect = self._is_disconnect
invalidate_pool_on_disconnect = not is_exit_exception
if self._reentrant_error:
util.raise_(
exc.DBAPIError.instance(
statement,
parameters,
e,
self.dialect.dbapi.Error,
hide_parameters=self.engine.hide_parameters,
dialect=self.dialect,
ismulti=context.executemany
if context is not None
else None,
),
with_traceback=exc_info[2],
from_=e,
)
self._reentrant_error = True
try:
# non-DBAPI error - if we already got a context,
# or there's no string statement, don't wrap it
should_wrap = isinstance(e, self.dialect.dbapi.Error) or (
statement is not None
and context is None
and not is_exit_exception
)
if should_wrap:
sqlalchemy_exception = exc.DBAPIError.instance(
statement,
parameters,
e,
self.dialect.dbapi.Error,
hide_parameters=self.engine.hide_parameters,
connection_invalidated=self._is_disconnect,
dialect=self.dialect,
ismulti=context.executemany
if context is not None
else None,
)
else:
sqlalchemy_exception = None
newraise = None
if (
self._has_events or self.engine._has_events
) and not self._execution_options.get(
"skip_user_error_events", False
):
# legacy dbapi_error event
if should_wrap and context:
self.dispatch.dbapi_error(
self, cursor, statement, parameters, context, e
)
# new handle_error event
ctx = ExceptionContextImpl(
e,
sqlalchemy_exception,
self.engine,
self,
cursor,
statement,
parameters,
context,
self._is_disconnect,
invalidate_pool_on_disconnect,
)
for fn in self.dispatch.handle_error:
try:
# handler returns an exception;
# call next handler in a chain
per_fn = fn(ctx)
if per_fn is not None:
ctx.chained_exception = newraise = per_fn
except Exception as _raised:
# handler raises an exception - stop processing
newraise = _raised
break
if self._is_disconnect != ctx.is_disconnect:
self._is_disconnect = ctx.is_disconnect
if sqlalchemy_exception:
sqlalchemy_exception.connection_invalidated = (
ctx.is_disconnect
)
# set up potentially user-defined value for
# invalidate pool.
invalidate_pool_on_disconnect = (
ctx.invalidate_pool_on_disconnect
)
if should_wrap and context:
context.handle_dbapi_exception(e)
if not self._is_disconnect:
if cursor:
self._safe_close_cursor(cursor)
with util.safe_reraise(warn_only=True):
self._autorollback()
if newraise:
util.raise_(newraise, with_traceback=exc_info[2], from_=e)
elif should_wrap:
util.raise_(
sqlalchemy_exception, with_traceback=exc_info[2], from_=e
)
else:
util.raise_(exc_info[1], with_traceback=exc_info[2])
finally:
del self._reentrant_error
if self._is_disconnect:
del self._is_disconnect
if not self.invalidated:
dbapi_conn_wrapper = self.__connection
if invalidate_pool_on_disconnect:
self.engine.pool._invalidate(dbapi_conn_wrapper, e)
self.invalidate(e)
if self.should_close_with_result:
self.close()
@classmethod
def _handle_dbapi_exception_noconnection(cls, e, dialect, engine):
exc_info = sys.exc_info()
is_disconnect = dialect.is_disconnect(e, None, None)
should_wrap = isinstance(e, dialect.dbapi.Error)
if should_wrap:
sqlalchemy_exception = exc.DBAPIError.instance(
None,
None,
e,
dialect.dbapi.Error,
hide_parameters=engine.hide_parameters,
connection_invalidated=is_disconnect,
)
else:
sqlalchemy_exception = None
newraise = None
if engine._has_events:
ctx = ExceptionContextImpl(
e,
sqlalchemy_exception,
engine,
None,
None,
None,
None,
None,
is_disconnect,
True,
)
for fn in engine.dispatch.handle_error:
try:
# handler returns an exception;
# call next handler in a chain
per_fn = fn(ctx)
if per_fn is not None:
ctx.chained_exception = newraise = per_fn
except Exception as _raised:
# handler raises an exception - stop processing
newraise = _raised
break
if sqlalchemy_exception and is_disconnect != ctx.is_disconnect:
sqlalchemy_exception.connection_invalidated = (
is_disconnect
) = ctx.is_disconnect
if newraise:
util.raise_(newraise, with_traceback=exc_info[2], from_=e)
elif should_wrap:
util.raise_(
sqlalchemy_exception, with_traceback=exc_info[2], from_=e
)
else:
util.raise_(exc_info[1], with_traceback=exc_info[2])
def transaction(self, callable_, *args, **kwargs):
r"""Execute the given function within a transaction boundary.
The function is passed this :class:`_engine.Connection`
as the first argument, followed by the given \*args and \**kwargs,
e.g.::
def do_something(conn, x, y):
conn.execute("some statement", {'x':x, 'y':y})
conn.transaction(do_something, 5, 10)
The operations inside the function are all invoked within the
context of a single :class:`.Transaction`.
Upon success, the transaction is committed. If an
exception is raised, the transaction is rolled back
before propagating the exception.
.. note::
The :meth:`.transaction` method is superseded by
the usage of the Python ``with:`` statement, which can
be used with :meth:`_engine.Connection.begin`::
with conn.begin():
conn.execute("some statement", {'x':5, 'y':10})
As well as with :meth:`_engine.Engine.begin`::
with engine.begin() as conn:
conn.execute("some statement", {'x':5, 'y':10})
.. seealso::
:meth:`_engine.Engine.begin` - engine-level transactional
context
:meth:`_engine.Engine.transaction` - engine-level version of
:meth:`_engine.Connection.transaction`
"""
trans = self.begin()
try:
ret = self.run_callable(callable_, *args, **kwargs)
trans.commit()
return ret
except:
with util.safe_reraise():
trans.rollback()
def run_callable(self, callable_, *args, **kwargs):
r"""Given a callable object or function, execute it, passing
a :class:`_engine.Connection` as the first argument.
The given \*args and \**kwargs are passed subsequent
to the :class:`_engine.Connection` argument.
This function, along with :meth:`_engine.Engine.run_callable`,
allows a function to be run with a :class:`_engine.Connection`
or :class:`_engine.Engine` object without the need to know
which one is being dealt with.
"""
return callable_(self, *args, **kwargs)
def _run_visitor(self, visitorcallable, element, **kwargs):
visitorcallable(self.dialect, self, **kwargs).traverse_single(element)
class ExceptionContextImpl(ExceptionContext):
"""Implement the :class:`.ExceptionContext` interface."""
def __init__(
self,
exception,
sqlalchemy_exception,
engine,
connection,
cursor,
statement,
parameters,
context,
is_disconnect,
invalidate_pool_on_disconnect,
):
self.engine = engine
self.connection = connection
self.sqlalchemy_exception = sqlalchemy_exception
self.original_exception = exception
self.execution_context = context
self.statement = statement
self.parameters = parameters
self.is_disconnect = is_disconnect
self.invalidate_pool_on_disconnect = invalidate_pool_on_disconnect
class Transaction(object):
"""Represent a database transaction in progress.
The :class:`.Transaction` object is procured by
calling the :meth:`_engine.Connection.begin` method of
:class:`_engine.Connection`::
from sqlalchemy import create_engine
engine = create_engine("postgresql://scott:tiger@localhost/test")
connection = engine.connect()
trans = connection.begin()
connection.execute("insert into x (a, b) values (1, 2)")
trans.commit()
The object provides :meth:`.rollback` and :meth:`.commit`
methods in order to control transaction boundaries. It
also implements a context manager interface so that
the Python ``with`` statement can be used with the
:meth:`_engine.Connection.begin` method::
with connection.begin():
connection.execute("insert into x (a, b) values (1, 2)")
The Transaction object is **not** threadsafe.
.. seealso::
:meth:`_engine.Connection.begin`
:meth:`_engine.Connection.begin_twophase`
:meth:`_engine.Connection.begin_nested`
.. index::
single: thread safety; Transaction
"""
def __init__(self, connection, parent):
self.connection = connection
self._actual_parent = parent
self.is_active = True
@property
def _parent(self):
return self._actual_parent or self
def close(self):
"""Close this :class:`.Transaction`.
If this transaction is the base transaction in a begin/commit
nesting, the transaction will rollback(). Otherwise, the
method returns.
This is used to cancel a Transaction without affecting the scope of
an enclosing transaction.
"""
if self._parent.is_active and self._parent is self:
self.rollback()
self.connection._discard_transaction(self)
def rollback(self):
"""Roll back this :class:`.Transaction`."""
if self._parent.is_active:
self._do_rollback()
self.is_active = False
def _do_rollback(self):
self._parent.rollback()
def commit(self):
"""Commit this :class:`.Transaction`."""
if not self._parent.is_active:
raise exc.InvalidRequestError("This transaction is inactive")
self._do_commit()
self.is_active = False
def _do_commit(self):
pass
def __enter__(self):
return self
def __exit__(self, type_, value, traceback):
if type_ is None and self.is_active:
try:
self.commit()
except:
with util.safe_reraise():
self.rollback()
else:
self.rollback()
class RootTransaction(Transaction):
def __init__(self, connection):
super(RootTransaction, self).__init__(connection, None)
self.connection._begin_impl(self)
def _do_rollback(self):
if self.is_active:
self.connection._rollback_impl()
def _do_commit(self):
if self.is_active:
self.connection._commit_impl()
class NestedTransaction(Transaction):
"""Represent a 'nested', or SAVEPOINT transaction.
A new :class:`.NestedTransaction` object may be procured
using the :meth:`_engine.Connection.begin_nested` method.
The interface is the same as that of :class:`.Transaction`.
"""
def __init__(self, connection, parent):
super(NestedTransaction, self).__init__(connection, parent)
self._savepoint = self.connection._savepoint_impl()
def _do_rollback(self):
if self.is_active:
self.connection._rollback_to_savepoint_impl(
self._savepoint, self._parent
)
def _do_commit(self):
if self.is_active:
self.connection._release_savepoint_impl(
self._savepoint, self._parent
)
class TwoPhaseTransaction(Transaction):
"""Represent a two-phase transaction.
A new :class:`.TwoPhaseTransaction` object may be procured
using the :meth:`_engine.Connection.begin_twophase` method.
The interface is the same as that of :class:`.Transaction`
with the addition of the :meth:`prepare` method.
"""
def __init__(self, connection, xid):
super(TwoPhaseTransaction, self).__init__(connection, None)
self._is_prepared = False
self.xid = xid
self.connection._begin_twophase_impl(self)
def prepare(self):
"""Prepare this :class:`.TwoPhaseTransaction`.
After a PREPARE, the transaction can be committed.
"""
if not self._parent.is_active:
raise exc.InvalidRequestError("This transaction is inactive")
self.connection._prepare_twophase_impl(self.xid)
self._is_prepared = True
def _do_rollback(self):
self.connection._rollback_twophase_impl(self.xid, self._is_prepared)
def _do_commit(self):
self.connection._commit_twophase_impl(self.xid, self._is_prepared)
class Engine(Connectable, log.Identified):
"""
Connects a :class:`~sqlalchemy.pool.Pool` and
:class:`~sqlalchemy.engine.interfaces.Dialect` together to provide a
source of database connectivity and behavior.
An :class:`_engine.Engine` object is instantiated publicly using the
:func:`~sqlalchemy.create_engine` function.
.. seealso::
:doc:`/core/engines`
:ref:`connections_toplevel`
"""
_execution_options = util.immutabledict()
_has_events = False
_connection_cls = Connection
schema_for_object = schema._schema_getter(None)
"""Return the ".schema" attribute for an object.
Used for :class:`_schema.Table`, :class:`.Sequence` and similar objects,
and takes into account
the :paramref:`.Connection.execution_options.schema_translate_map`
parameter.
.. versionadded:: 1.1
.. seealso::
:ref:`schema_translating`
"""
def __init__(
self,
pool,
dialect,
url,
logging_name=None,
echo=None,
proxy=None,
execution_options=None,
hide_parameters=False,
):
self.pool = pool
self.url = url
self.dialect = dialect
if logging_name:
self.logging_name = logging_name
self.echo = echo
self.hide_parameters = hide_parameters
log.instance_logger(self, echoflag=echo)
if proxy:
interfaces.ConnectionProxy._adapt_listener(self, proxy)
if execution_options:
self.update_execution_options(**execution_options)
@property
def engine(self):
return self
def update_execution_options(self, **opt):
r"""Update the default execution_options dictionary
of this :class:`_engine.Engine`.
The given keys/values in \**opt are added to the
default execution options that will be used for
all connections. The initial contents of this dictionary
can be sent via the ``execution_options`` parameter
to :func:`_sa.create_engine`.
.. seealso::
:meth:`_engine.Connection.execution_options`
:meth:`_engine.Engine.execution_options`
"""
self._execution_options = self._execution_options.union(opt)
self.dispatch.set_engine_execution_options(self, opt)
self.dialect.set_engine_execution_options(self, opt)
def execution_options(self, **opt):
"""Return a new :class:`_engine.Engine` that will provide
:class:`_engine.Connection` objects with the given execution options.
The returned :class:`_engine.Engine` remains related to the original
:class:`_engine.Engine` in that it shares the same connection pool and
other state:
* The :class:`_pool.Pool` used by the new :class:`_engine.Engine`
is the
same instance. The :meth:`_engine.Engine.dispose`
method will replace
the connection pool instance for the parent engine as well
as this one.
* Event listeners are "cascaded" - meaning, the new
:class:`_engine.Engine`
inherits the events of the parent, and new events can be associated
with the new :class:`_engine.Engine` individually.
* The logging configuration and logging_name is copied from the parent
:class:`_engine.Engine`.
The intent of the :meth:`_engine.Engine.execution_options` method is
to implement "sharding" schemes where multiple :class:`_engine.Engine`
objects refer to the same connection pool, but are differentiated
by options that would be consumed by a custom event::
primary_engine = create_engine("mysql://")
shard1 = primary_engine.execution_options(shard_id="shard1")
shard2 = primary_engine.execution_options(shard_id="shard2")
Above, the ``shard1`` engine serves as a factory for
:class:`_engine.Connection`
objects that will contain the execution option
``shard_id=shard1``, and ``shard2`` will produce
:class:`_engine.Connection`
objects that contain the execution option ``shard_id=shard2``.
An event handler can consume the above execution option to perform
a schema switch or other operation, given a connection. Below
we emit a MySQL ``use`` statement to switch databases, at the same
time keeping track of which database we've established using the
:attr:`_engine.Connection.info` dictionary,
which gives us a persistent
storage space that follows the DBAPI connection::
from sqlalchemy import event
from sqlalchemy.engine import Engine
shards = {"default": "base", shard_1: "db1", "shard_2": "db2"}
@event.listens_for(Engine, "before_cursor_execute")
def _switch_shard(conn, cursor, stmt,
params, context, executemany):
shard_id = conn._execution_options.get('shard_id', "default")
current_shard = conn.info.get("current_shard", None)
if current_shard != shard_id:
cursor.execute("use %s" % shards[shard_id])
conn.info["current_shard"] = shard_id
.. seealso::
:meth:`_engine.Connection.execution_options`
- update execution options
on a :class:`_engine.Connection` object.
:meth:`_engine.Engine.update_execution_options`
- update the execution
options for a given :class:`_engine.Engine` in place.
:meth:`_engine.Engine.get_execution_options`
"""
return OptionEngine(self, opt)
def get_execution_options(self):
"""Get the non-SQL options which will take effect during execution.
.. versionadded: 1.3
.. seealso::
:meth:`_engine.Engine.execution_options`
"""
return self._execution_options
@property
def name(self):
"""String name of the :class:`~sqlalchemy.engine.interfaces.Dialect`
in use by this :class:`Engine`."""
return self.dialect.name
@property
def driver(self):
"""Driver name of the :class:`~sqlalchemy.engine.interfaces.Dialect`
in use by this :class:`Engine`."""
return self.dialect.driver
echo = log.echo_property()
def __repr__(self):
return "Engine(%r)" % self.url
def dispose(self):
"""Dispose of the connection pool used by this
:class:`_engine.Engine`.
This has the effect of fully closing all **currently checked in**
database connections. Connections that are still checked out
will **not** be closed, however they will no longer be associated
with this :class:`_engine.Engine`,
so when they are closed individually,
eventually the :class:`_pool.Pool` which they are associated with will
be garbage collected and they will be closed out fully, if
not already closed on checkin.
A new connection pool is created immediately after the old one has
been disposed. This new pool, like all SQLAlchemy connection pools,
does not make any actual connections to the database until one is
first requested, so as long as the :class:`_engine.Engine`
isn't used again,
no new connections will be made.
.. seealso::
:ref:`engine_disposal`
"""
self.pool.dispose()
self.pool = self.pool.recreate()
self.dispatch.engine_disposed(self)
def _execute_default(self, default):
with self._contextual_connect() as conn:
return conn._execute_default(default, (), {})
@contextlib.contextmanager
def _optional_conn_ctx_manager(self, connection=None):
if connection is None:
with self._contextual_connect() as conn:
yield conn
else:
yield connection
def _run_visitor(
self, visitorcallable, element, connection=None, **kwargs
):
with self._optional_conn_ctx_manager(connection) as conn:
conn._run_visitor(visitorcallable, element, **kwargs)
class _trans_ctx(object):
def __init__(self, conn, transaction, close_with_result):
self.conn = conn
self.transaction = transaction
self.close_with_result = close_with_result
def __enter__(self):
return self.conn
def __exit__(self, type_, value, traceback):
if type_ is not None:
self.transaction.rollback()
else:
self.transaction.commit()
if not self.close_with_result:
self.conn.close()
def begin(self, close_with_result=False):
"""Return a context manager delivering a :class:`_engine.Connection`
with a :class:`.Transaction` established.
E.g.::
with engine.begin() as conn:
conn.execute("insert into table (x, y, z) values (1, 2, 3)")
conn.execute("my_special_procedure(5)")
Upon successful operation, the :class:`.Transaction`
is committed. If an error is raised, the :class:`.Transaction`
is rolled back.
The ``close_with_result`` flag is normally ``False``, and indicates
that the :class:`_engine.Connection` will be closed when the operation
is complete. When set to ``True``, it indicates the
:class:`_engine.Connection` is in "single use" mode, where the
:class:`_engine.ResultProxy` returned by the first call to
:meth:`_engine.Connection.execute` will close the
:class:`_engine.Connection` when
that :class:`_engine.ResultProxy` has exhausted all result rows.
.. seealso::
:meth:`_engine.Engine.connect` - procure a
:class:`_engine.Connection` from
an :class:`_engine.Engine`.
:meth:`_engine.Connection.begin` - start a :class:`.Transaction`
for a particular :class:`_engine.Connection`.
"""
conn = self._contextual_connect(close_with_result=close_with_result)
try:
trans = conn.begin()
except:
with util.safe_reraise():
conn.close()
return Engine._trans_ctx(conn, trans, close_with_result)
def transaction(self, callable_, *args, **kwargs):
r"""Execute the given function within a transaction boundary.
The function is passed a :class:`_engine.Connection` newly procured
from :meth:`_engine.Engine.contextual_connect` as the first argument,
followed by the given \*args and \**kwargs.
e.g.::
def do_something(conn, x, y):
conn.execute("some statement", {'x':x, 'y':y})
engine.transaction(do_something, 5, 10)
The operations inside the function are all invoked within the
context of a single :class:`.Transaction`.
Upon success, the transaction is committed. If an
exception is raised, the transaction is rolled back
before propagating the exception.
.. note::
The :meth:`.transaction` method is superseded by
the usage of the Python ``with:`` statement, which can
be used with :meth:`_engine.Engine.begin`::
with engine.begin() as conn:
conn.execute("some statement", {'x':5, 'y':10})
.. seealso::
:meth:`_engine.Engine.begin` - engine-level transactional
context
:meth:`_engine.Connection.transaction`
- connection-level version of
:meth:`_engine.Engine.transaction`
"""
with self._contextual_connect() as conn:
return conn.transaction(callable_, *args, **kwargs)
def run_callable(self, callable_, *args, **kwargs):
r"""Given a callable object or function, execute it, passing
a :class:`_engine.Connection` as the first argument.
The given \*args and \**kwargs are passed subsequent
to the :class:`_engine.Connection` argument.
This function, along with :meth:`_engine.Connection.run_callable`,
allows a function to be run with a :class:`_engine.Connection`
or :class:`_engine.Engine` object without the need to know
which one is being dealt with.
"""
with self._contextual_connect() as conn:
return conn.run_callable(callable_, *args, **kwargs)
def execute(self, statement, *multiparams, **params):
"""Executes the given construct and returns a
:class:`_engine.ResultProxy`.
The arguments are the same as those used by
:meth:`_engine.Connection.execute`.
Here, a :class:`_engine.Connection` is acquired using the
:meth:`_engine.Engine.contextual_connect` method,
and the statement executed
with that connection. The returned :class:`_engine.ResultProxy`
is flagged
such that when the :class:`_engine.ResultProxy` is exhausted and its
underlying cursor is closed, the :class:`_engine.Connection`
created here
will also be closed, which allows its associated DBAPI connection
resource to be returned to the connection pool.
"""
connection = self._contextual_connect(close_with_result=True)
return connection.execute(statement, *multiparams, **params)
def scalar(self, statement, *multiparams, **params):
return self.execute(statement, *multiparams, **params).scalar()
def _execute_clauseelement(self, elem, multiparams=None, params=None):
connection = self._contextual_connect(close_with_result=True)
return connection._execute_clauseelement(elem, multiparams, params)
def _execute_compiled(self, compiled, multiparams, params):
connection = self._contextual_connect(close_with_result=True)
return connection._execute_compiled(compiled, multiparams, params)
def connect(self, **kwargs):
"""Return a new :class:`_engine.Connection` object.
The :class:`_engine.Connection` object is a facade that uses a DBAPI
connection internally in order to communicate with the database. This
connection is procured from the connection-holding :class:`_pool.Pool`
referenced by this :class:`_engine.Engine`. When the
:meth:`_engine.Connection.close` method of the
:class:`_engine.Connection` object
is called, the underlying DBAPI connection is then returned to the
connection pool, where it may be used again in a subsequent call to
:meth:`_engine.Engine.connect`.
"""
return self._connection_cls(self, **kwargs)
@util.deprecated(
"1.3",
"The :meth:`_engine.Engine.contextual_connect` method is deprecated. "
"This "
"method is an artifact of the threadlocal engine strategy which is "
"also to be deprecated. For explicit connections from an "
":class:`_engine.Engine`, use the :meth:`_engine.Engine.connect` "
"method.",
)
def contextual_connect(self, close_with_result=False, **kwargs):
"""Return a :class:`_engine.Connection`
object which may be part of some
ongoing context.
By default, this method does the same thing as
:meth:`_engine.Engine.connect`.
Subclasses of :class:`_engine.Engine` may override this method
to provide contextual behavior.
:param close_with_result: When True, the first
:class:`_engine.ResultProxy`
created by the :class:`_engine.Connection` will call the
:meth:`_engine.Connection.close`
method of that connection as soon as any
pending result rows are exhausted. This is used to supply the
"connectionless execution" behavior provided by the
:meth:`_engine.Engine.execute` method.
"""
return self._contextual_connect(
close_with_result=close_with_result, **kwargs
)
def _contextual_connect(self, close_with_result=False, **kwargs):
return self._connection_cls(
self,
self._wrap_pool_connect(self.pool.connect, None),
close_with_result=close_with_result,
**kwargs
)
def table_names(self, schema=None, connection=None):
"""Return a list of all table names available in the database.
:param schema: Optional, retrieve names from a non-default schema.
:param connection: Optional, use a specified connection. Default is
the ``contextual_connect`` for this ``Engine``.
"""
with self._optional_conn_ctx_manager(connection) as conn:
return self.dialect.get_table_names(conn, schema)
def has_table(self, table_name, schema=None):
"""Return True if the given backend has a table of the given name.
.. seealso::
:ref:`metadata_reflection_inspector` - detailed schema inspection
using the :class:`_reflection.Inspector` interface.
:class:`.quoted_name` - used to pass quoting information along
with a schema identifier.
"""
return self.run_callable(self.dialect.has_table, table_name, schema)
def _wrap_pool_connect(self, fn, connection):
dialect = self.dialect
try:
return fn()
except dialect.dbapi.Error as e:
if connection is None:
Connection._handle_dbapi_exception_noconnection(
e, dialect, self
)
else:
util.raise_(
sys.exc_info()[1], with_traceback=sys.exc_info()[2]
)
def raw_connection(self, _connection=None):
"""Return a "raw" DBAPI connection from the connection pool.
The returned object is a proxied version of the DBAPI
connection object used by the underlying driver in use.
The object will have all the same behavior as the real DBAPI
connection, except that its ``close()`` method will result in the
connection being returned to the pool, rather than being closed
for real.
This method provides direct DBAPI connection access for
special situations when the API provided by
:class:`_engine.Connection`
is not needed. When a :class:`_engine.Connection` object is already
present, the DBAPI connection is available using
the :attr:`_engine.Connection.connection` accessor.
.. seealso::
:ref:`dbapi_connections`
"""
return self._wrap_pool_connect(
self.pool.unique_connection, _connection
)
class OptionEngine(Engine):
_sa_propagate_class_events = False
def __init__(self, proxied, execution_options):
self._proxied = proxied
self.url = proxied.url
self.dialect = proxied.dialect
self.logging_name = proxied.logging_name
self.echo = proxied.echo
self.hide_parameters = proxied.hide_parameters
log.instance_logger(self, echoflag=self.echo)
# note: this will propagate events that are assigned to the parent
# engine after this OptionEngine is created. Since we share
# the events of the parent we also disallow class-level events
# to apply to the OptionEngine class directly.
#
# the other way this can work would be to transfer existing
# events only, using:
# self.dispatch._update(proxied.dispatch)
#
# that might be more appropriate however it would be a behavioral
# change for logic that assigns events to the parent engine and
# would like it to take effect for the already-created sub-engine.
self.dispatch = self.dispatch._join(proxied.dispatch)
self._execution_options = proxied._execution_options
self.update_execution_options(**execution_options)
def _get_pool(self):
return self._proxied.pool
def _set_pool(self, pool):
self._proxied.pool = pool
pool = property(_get_pool, _set_pool)
def _get_has_events(self):
return self._proxied._has_events or self.__dict__.get(
"_has_events", False
)
def _set_has_events(self, value):
self.__dict__["_has_events"] = value
_has_events = property(_get_has_events, _set_has_events)
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