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1# engine/create.py
2# Copyright (C) 2005-2023 the SQLAlchemy authors and contributors
3# <see AUTHORS file>
4#
5# This module is part of SQLAlchemy and is released under
6# the MIT License: https://www.opensource.org/licenses/mit-license.php
9from . import base
10from . import url as _url
11from .mock import create_mock_engine
12from .. import event
13from .. import exc
14from .. import pool as poollib
15from .. import util
16from ..sql import compiler
19@util.deprecated_params(
20 strategy=(
21 "1.4",
22 "The :paramref:`_sa.create_engine.strategy` keyword is deprecated, "
23 "and the only argument accepted is 'mock'; please use "
24 ":func:`.create_mock_engine` going forward. For general "
25 "customization of create_engine which may have been accomplished "
26 "using strategies, see :class:`.CreateEnginePlugin`.",
27 ),
28 empty_in_strategy=(
29 "1.4",
30 "The :paramref:`_sa.create_engine.empty_in_strategy` keyword is "
31 "deprecated, and no longer has any effect. All IN expressions "
32 "are now rendered using "
33 'the "expanding parameter" strategy which renders a set of bound'
34 'expressions, or an "empty set" SELECT, at statement execution'
35 "time.",
36 ),
37 case_sensitive=(
38 "1.4",
39 "The :paramref:`_sa.create_engine.case_sensitive` parameter "
40 "is deprecated and will be removed in a future release. "
41 "Applications should work with result column names in a case "
42 "sensitive fashion.",
43 ),
44)
45def create_engine(url, **kwargs):
46 """Create a new :class:`_engine.Engine` instance.
48 The standard calling form is to send the :ref:`URL <database_urls>` as the
49 first positional argument, usually a string
50 that indicates database dialect and connection arguments::
52 engine = create_engine("postgresql://scott:tiger@localhost/test")
54 .. note::
56 Please review :ref:`database_urls` for general guidelines in composing
57 URL strings. In particular, special characters, such as those often
58 part of passwords, must be URL encoded to be properly parsed.
60 Additional keyword arguments may then follow it which
61 establish various options on the resulting :class:`_engine.Engine`
62 and its underlying :class:`.Dialect` and :class:`_pool.Pool`
63 constructs::
65 engine = create_engine("mysql://scott:tiger@hostname/dbname",
66 encoding='latin1', echo=True)
68 The string form of the URL is
69 ``dialect[+driver]://user:password@host/dbname[?key=value..]``, where
70 ``dialect`` is a database name such as ``mysql``, ``oracle``,
71 ``postgresql``, etc., and ``driver`` the name of a DBAPI, such as
72 ``psycopg2``, ``pyodbc``, ``cx_oracle``, etc. Alternatively,
73 the URL can be an instance of :class:`~sqlalchemy.engine.url.URL`.
75 ``**kwargs`` takes a wide variety of options which are routed
76 towards their appropriate components. Arguments may be specific to
77 the :class:`_engine.Engine`, the underlying :class:`.Dialect`,
78 as well as the
79 :class:`_pool.Pool`. Specific dialects also accept keyword arguments that
80 are unique to that dialect. Here, we describe the parameters
81 that are common to most :func:`_sa.create_engine()` usage.
83 Once established, the newly resulting :class:`_engine.Engine` will
84 request a connection from the underlying :class:`_pool.Pool` once
85 :meth:`_engine.Engine.connect` is called, or a method which depends on it
86 such as :meth:`_engine.Engine.execute` is invoked. The
87 :class:`_pool.Pool` in turn
88 will establish the first actual DBAPI connection when this request
89 is received. The :func:`_sa.create_engine` call itself does **not**
90 establish any actual DBAPI connections directly.
92 .. seealso::
94 :doc:`/core/engines`
96 :doc:`/dialects/index`
98 :ref:`connections_toplevel`
100 :param case_sensitive: if False, result column names
101 will match in a case-insensitive fashion, that is,
102 ``row['SomeColumn']``.
104 :param connect_args: a dictionary of options which will be
105 passed directly to the DBAPI's ``connect()`` method as
106 additional keyword arguments. See the example
107 at :ref:`custom_dbapi_args`.
109 :param convert_unicode=False: if set to True, causes
110 all :class:`.String` datatypes to act as though the
111 :paramref:`.String.convert_unicode` flag has been set to ``True``,
112 regardless of a setting of ``False`` on an individual :class:`.String`
113 type. This has the effect of causing all :class:`.String` -based
114 columns to accommodate Python Unicode objects directly as though the
115 datatype were the :class:`.Unicode` type.
117 .. deprecated:: 1.3
119 The :paramref:`_sa.create_engine.convert_unicode` parameter
120 is deprecated and will be removed in a future release.
121 All modern DBAPIs now support Python Unicode directly and this
122 parameter is unnecessary.
124 :param creator: a callable which returns a DBAPI connection.
125 This creation function will be passed to the underlying
126 connection pool and will be used to create all new database
127 connections. Usage of this function causes connection
128 parameters specified in the URL argument to be bypassed.
130 This hook is not as flexible as the newer
131 :meth:`_events.DialectEvents.do_connect` hook which allows complete
132 control over how a connection is made to the database, given the full
133 set of URL arguments and state beforehand.
135 .. seealso::
137 :meth:`_events.DialectEvents.do_connect` - event hook that allows
138 full control over DBAPI connection mechanics.
140 :ref:`custom_dbapi_args`
142 :param echo=False: if True, the Engine will log all statements
143 as well as a ``repr()`` of their parameter lists to the default log
144 handler, which defaults to ``sys.stdout`` for output. If set to the
145 string ``"debug"``, result rows will be printed to the standard output
146 as well. The ``echo`` attribute of ``Engine`` can be modified at any
147 time to turn logging on and off; direct control of logging is also
148 available using the standard Python ``logging`` module.
150 .. seealso::
152 :ref:`dbengine_logging` - further detail on how to configure
153 logging.
156 :param echo_pool=False: if True, the connection pool will log
157 informational output such as when connections are invalidated
158 as well as when connections are recycled to the default log handler,
159 which defaults to ``sys.stdout`` for output. If set to the string
160 ``"debug"``, the logging will include pool checkouts and checkins.
161 Direct control of logging is also available using the standard Python
162 ``logging`` module.
164 .. seealso::
166 :ref:`dbengine_logging` - further detail on how to configure
167 logging.
170 :param empty_in_strategy: No longer used; SQLAlchemy now uses
171 "empty set" behavior for IN in all cases.
173 :param enable_from_linting: defaults to True. Will emit a warning
174 if a given SELECT statement is found to have un-linked FROM elements
175 which would cause a cartesian product.
177 .. versionadded:: 1.4
179 .. seealso::
181 :ref:`change_4737`
183 :param encoding: **legacy Python 2 value only, where it only applies to
184 specific DBAPIs, not used in Python 3 for any modern DBAPI driver.
185 Please refer to individual dialect documentation for client encoding
186 behaviors.** Defaults to the string value ``utf-8``. This value
187 refers **only** to the character encoding that is used when SQLAlchemy
188 sends or receives data from a :term:`DBAPI` that does not support
189 Python Unicode and **is only used under Python 2**, only for certain
190 DBAPI drivers, and only in certain circumstances. **Python 3 users
191 please DISREGARD this parameter and refer to the documentation for the
192 specific dialect in use in order to configure character encoding
193 behavior.**
195 .. note:: The ``encoding`` parameter deals only with in-Python
196 encoding issues that were prevalent with **some DBAPIS only**
197 under **Python 2 only**. Under Python 3 it is not used by
198 any modern dialect. For DBAPIs that require
199 client encoding configurations, which are most of those outside
200 of SQLite, please consult specific :ref:`dialect documentation
201 <dialect_toplevel>` for details.
203 All modern DBAPIs that work in Python 3 necessarily feature direct
204 support for Python unicode strings. Under Python 2, this was not
205 always the case. For those scenarios where the DBAPI is detected as
206 not supporting a Python ``unicode`` object under Python 2, this
207 encoding is used to determine the source/destination encoding. It is
208 **not used** for those cases where the DBAPI handles unicode directly.
210 To properly configure a system to accommodate Python ``unicode``
211 objects, the DBAPI should be configured to handle unicode to the
212 greatest degree as is appropriate - see the notes on unicode pertaining
213 to the specific target database in use at :ref:`dialect_toplevel`.
215 Areas where string encoding may need to be accommodated
216 outside of the DBAPI, nearly always under **Python 2 only**,
217 include zero or more of:
219 * the values passed to bound parameters, corresponding to
220 the :class:`.Unicode` type or the :class:`.String` type
221 when ``convert_unicode`` is ``True``;
222 * the values returned in result set columns corresponding
223 to the :class:`.Unicode` type or the :class:`.String`
224 type when ``convert_unicode`` is ``True``;
225 * the string SQL statement passed to the DBAPI's
226 ``cursor.execute()`` method;
227 * the string names of the keys in the bound parameter
228 dictionary passed to the DBAPI's ``cursor.execute()``
229 as well as ``cursor.setinputsizes()`` methods;
230 * the string column names retrieved from the DBAPI's
231 ``cursor.description`` attribute.
233 When using Python 3, the DBAPI is required to support all of the above
234 values as Python ``unicode`` objects, which in Python 3 are just known
235 as ``str``. In Python 2, the DBAPI does not specify unicode behavior
236 at all, so SQLAlchemy must make decisions for each of the above values
237 on a per-DBAPI basis - implementations are completely inconsistent in
238 their behavior.
240 :param execution_options: Dictionary execution options which will
241 be applied to all connections. See
242 :meth:`~sqlalchemy.engine.Connection.execution_options`
244 :param future: Use the 2.0 style :class:`_future.Engine` and
245 :class:`_future.Connection` API.
247 .. versionadded:: 1.4
249 .. seealso::
251 :ref:`migration_20_toplevel`
253 :param hide_parameters: Boolean, when set to True, SQL statement parameters
254 will not be displayed in INFO logging nor will they be formatted into
255 the string representation of :class:`.StatementError` objects.
257 .. versionadded:: 1.3.8
259 .. seealso::
261 :ref:`dbengine_logging` - further detail on how to configure
262 logging.
264 :param implicit_returning=True: Legacy flag that when set to ``False``
265 will disable the use of ``RETURNING`` on supporting backends where it
266 would normally be used to fetch newly generated primary key values for
267 single-row INSERT statements that do not otherwise specify a RETURNING
268 clause. This behavior applies primarily to the PostgreSQL, Oracle,
269 SQL Server backends.
271 .. warning:: this flag originally allowed the "implicit returning"
272 feature to be *enabled* back when it was very new and there was not
273 well-established database support. In modern SQLAlchemy, this flag
274 should **always be set to True**. Some SQLAlchemy features will
275 fail to function properly if this flag is set to ``False``.
277 :param isolation_level: this string parameter is interpreted by various
278 dialects in order to affect the transaction isolation level of the
279 database connection. The parameter essentially accepts some subset of
280 these string arguments: ``"SERIALIZABLE"``, ``"REPEATABLE READ"``,
281 ``"READ COMMITTED"``, ``"READ UNCOMMITTED"`` and ``"AUTOCOMMIT"``.
282 Behavior here varies per backend, and
283 individual dialects should be consulted directly.
285 Note that the isolation level can also be set on a
286 per-:class:`_engine.Connection` basis as well, using the
287 :paramref:`.Connection.execution_options.isolation_level`
288 feature.
290 .. seealso::
292 :ref:`dbapi_autocommit`
294 :param json_deserializer: for dialects that support the
295 :class:`_types.JSON`
296 datatype, this is a Python callable that will convert a JSON string
297 to a Python object. By default, the Python ``json.loads`` function is
298 used.
300 .. versionchanged:: 1.3.7 The SQLite dialect renamed this from
301 ``_json_deserializer``.
303 :param json_serializer: for dialects that support the :class:`_types.JSON`
304 datatype, this is a Python callable that will render a given object
305 as JSON. By default, the Python ``json.dumps`` function is used.
307 .. versionchanged:: 1.3.7 The SQLite dialect renamed this from
308 ``_json_serializer``.
311 :param label_length=None: optional integer value which limits
312 the size of dynamically generated column labels to that many
313 characters. If less than 6, labels are generated as
314 "_(counter)". If ``None``, the value of
315 ``dialect.max_identifier_length``, which may be affected via the
316 :paramref:`_sa.create_engine.max_identifier_length` parameter,
317 is used instead. The value of
318 :paramref:`_sa.create_engine.label_length`
319 may not be larger than that of
320 :paramref:`_sa.create_engine.max_identfier_length`.
322 .. seealso::
324 :paramref:`_sa.create_engine.max_identifier_length`
326 :param logging_name: String identifier which will be used within
327 the "name" field of logging records generated within the
328 "sqlalchemy.engine" logger. Defaults to a hexstring of the
329 object's id.
331 .. seealso::
333 :ref:`dbengine_logging` - further detail on how to configure
334 logging.
336 :paramref:`_engine.Connection.execution_options.logging_token`
340 :param max_identifier_length: integer; override the max_identifier_length
341 determined by the dialect. if ``None`` or zero, has no effect. This
342 is the database's configured maximum number of characters that may be
343 used in a SQL identifier such as a table name, column name, or label
344 name. All dialects determine this value automatically, however in the
345 case of a new database version for which this value has changed but
346 SQLAlchemy's dialect has not been adjusted, the value may be passed
347 here.
349 .. versionadded:: 1.3.9
351 .. seealso::
353 :paramref:`_sa.create_engine.label_length`
355 :param max_overflow=10: the number of connections to allow in
356 connection pool "overflow", that is connections that can be
357 opened above and beyond the pool_size setting, which defaults
358 to five. this is only used with :class:`~sqlalchemy.pool.QueuePool`.
360 :param module=None: reference to a Python module object (the module
361 itself, not its string name). Specifies an alternate DBAPI module to
362 be used by the engine's dialect. Each sub-dialect references a
363 specific DBAPI which will be imported before first connect. This
364 parameter causes the import to be bypassed, and the given module to
365 be used instead. Can be used for testing of DBAPIs as well as to
366 inject "mock" DBAPI implementations into the :class:`_engine.Engine`.
368 :param paramstyle=None: The `paramstyle <https://legacy.python.org/dev/peps/pep-0249/#paramstyle>`_
369 to use when rendering bound parameters. This style defaults to the
370 one recommended by the DBAPI itself, which is retrieved from the
371 ``.paramstyle`` attribute of the DBAPI. However, most DBAPIs accept
372 more than one paramstyle, and in particular it may be desirable
373 to change a "named" paramstyle into a "positional" one, or vice versa.
374 When this attribute is passed, it should be one of the values
375 ``"qmark"``, ``"numeric"``, ``"named"``, ``"format"`` or
376 ``"pyformat"``, and should correspond to a parameter style known
377 to be supported by the DBAPI in use.
379 :param pool=None: an already-constructed instance of
380 :class:`~sqlalchemy.pool.Pool`, such as a
381 :class:`~sqlalchemy.pool.QueuePool` instance. If non-None, this
382 pool will be used directly as the underlying connection pool
383 for the engine, bypassing whatever connection parameters are
384 present in the URL argument. For information on constructing
385 connection pools manually, see :ref:`pooling_toplevel`.
387 :param poolclass=None: a :class:`~sqlalchemy.pool.Pool`
388 subclass, which will be used to create a connection pool
389 instance using the connection parameters given in the URL. Note
390 this differs from ``pool`` in that you don't actually
391 instantiate the pool in this case, you just indicate what type
392 of pool to be used.
394 :param pool_logging_name: String identifier which will be used within
395 the "name" field of logging records generated within the
396 "sqlalchemy.pool" logger. Defaults to a hexstring of the object's
397 id.
400 .. seealso::
402 :ref:`dbengine_logging` - further detail on how to configure
403 logging.
406 :param pool_pre_ping: boolean, if True will enable the connection pool
407 "pre-ping" feature that tests connections for liveness upon
408 each checkout.
410 .. versionadded:: 1.2
412 .. seealso::
414 :ref:`pool_disconnects_pessimistic`
416 :param pool_size=5: the number of connections to keep open
417 inside the connection pool. This used with
418 :class:`~sqlalchemy.pool.QueuePool` as
419 well as :class:`~sqlalchemy.pool.SingletonThreadPool`. With
420 :class:`~sqlalchemy.pool.QueuePool`, a ``pool_size`` setting
421 of 0 indicates no limit; to disable pooling, set ``poolclass`` to
422 :class:`~sqlalchemy.pool.NullPool` instead.
424 :param pool_recycle=-1: this setting causes the pool to recycle
425 connections after the given number of seconds has passed. It
426 defaults to -1, or no timeout. For example, setting to 3600
427 means connections will be recycled after one hour. Note that
428 MySQL in particular will disconnect automatically if no
429 activity is detected on a connection for eight hours (although
430 this is configurable with the MySQLDB connection itself and the
431 server configuration as well).
433 .. seealso::
435 :ref:`pool_setting_recycle`
437 :param pool_reset_on_return='rollback': set the
438 :paramref:`_pool.Pool.reset_on_return` parameter of the underlying
439 :class:`_pool.Pool` object, which can be set to the values
440 ``"rollback"``, ``"commit"``, or ``None``.
442 .. seealso::
444 :ref:`pool_reset_on_return`
446 :param pool_timeout=30: number of seconds to wait before giving
447 up on getting a connection from the pool. This is only used
448 with :class:`~sqlalchemy.pool.QueuePool`. This can be a float but is
449 subject to the limitations of Python time functions which may not be
450 reliable in the tens of milliseconds.
452 .. note: don't use 30.0 above, it seems to break with the :param tag
454 :param pool_use_lifo=False: use LIFO (last-in-first-out) when retrieving
455 connections from :class:`.QueuePool` instead of FIFO
456 (first-in-first-out). Using LIFO, a server-side timeout scheme can
457 reduce the number of connections used during non- peak periods of
458 use. When planning for server-side timeouts, ensure that a recycle or
459 pre-ping strategy is in use to gracefully handle stale connections.
461 .. versionadded:: 1.3
463 .. seealso::
465 :ref:`pool_use_lifo`
467 :ref:`pool_disconnects`
469 :param plugins: string list of plugin names to load. See
470 :class:`.CreateEnginePlugin` for background.
472 .. versionadded:: 1.2.3
474 :param query_cache_size: size of the cache used to cache the SQL string
475 form of queries. Set to zero to disable caching.
477 The cache is pruned of its least recently used items when its size reaches
478 N * 1.5. Defaults to 500, meaning the cache will always store at least
479 500 SQL statements when filled, and will grow up to 750 items at which
480 point it is pruned back down to 500 by removing the 250 least recently
481 used items.
483 Caching is accomplished on a per-statement basis by generating a
484 cache key that represents the statement's structure, then generating
485 string SQL for the current dialect only if that key is not present
486 in the cache. All statements support caching, however some features
487 such as an INSERT with a large set of parameters will intentionally
488 bypass the cache. SQL logging will indicate statistics for each
489 statement whether or not it were pull from the cache.
491 .. note:: some ORM functions related to unit-of-work persistence as well
492 as some attribute loading strategies will make use of individual
493 per-mapper caches outside of the main cache.
496 .. seealso::
498 :ref:`sql_caching`
500 .. versionadded:: 1.4
502 """ # noqa
504 if "strategy" in kwargs:
505 strat = kwargs.pop("strategy")
506 if strat == "mock":
507 return create_mock_engine(url, **kwargs)
508 else:
509 raise exc.ArgumentError("unknown strategy: %r" % strat)
511 kwargs.pop("empty_in_strategy", None)
513 # create url.URL object
514 u = _url.make_url(url)
516 u, plugins, kwargs = u._instantiate_plugins(kwargs)
518 entrypoint = u._get_entrypoint()
519 dialect_cls = entrypoint.get_dialect_cls(u)
521 if kwargs.pop("_coerce_config", False):
523 def pop_kwarg(key, default=None):
524 value = kwargs.pop(key, default)
525 if key in dialect_cls.engine_config_types:
526 value = dialect_cls.engine_config_types[key](value)
527 return value
529 else:
530 pop_kwarg = kwargs.pop
532 dialect_args = {}
533 # consume dialect arguments from kwargs
534 for k in util.get_cls_kwargs(dialect_cls):
535 if k in kwargs:
536 dialect_args[k] = pop_kwarg(k)
538 dbapi = kwargs.pop("module", None)
539 if dbapi is None:
540 dbapi_args = {}
541 for k in util.get_func_kwargs(dialect_cls.dbapi):
542 if k in kwargs:
543 dbapi_args[k] = pop_kwarg(k)
544 dbapi = dialect_cls.dbapi(**dbapi_args)
546 dialect_args["dbapi"] = dbapi
548 dialect_args.setdefault("compiler_linting", compiler.NO_LINTING)
549 enable_from_linting = kwargs.pop("enable_from_linting", True)
550 if enable_from_linting:
551 dialect_args["compiler_linting"] ^= compiler.COLLECT_CARTESIAN_PRODUCTS
553 for plugin in plugins:
554 plugin.handle_dialect_kwargs(dialect_cls, dialect_args)
556 # create dialect
557 dialect = dialect_cls(**dialect_args)
559 # assemble connection arguments
560 (cargs, cparams) = dialect.create_connect_args(u)
561 cparams.update(pop_kwarg("connect_args", {}))
562 cargs = list(cargs) # allow mutability
564 # look for existing pool or create
565 pool = pop_kwarg("pool", None)
566 if pool is None:
568 def connect(connection_record=None):
569 if dialect._has_events:
570 for fn in dialect.dispatch.do_connect:
571 connection = fn(dialect, connection_record, cargs, cparams)
572 if connection is not None:
573 return connection
574 return dialect.connect(*cargs, **cparams)
576 creator = pop_kwarg("creator", connect)
578 poolclass = pop_kwarg("poolclass", None)
579 if poolclass is None:
580 poolclass = dialect.get_dialect_pool_class(u)
581 pool_args = {"dialect": dialect}
583 # consume pool arguments from kwargs, translating a few of
584 # the arguments
585 translate = {
586 "logging_name": "pool_logging_name",
587 "echo": "echo_pool",
588 "timeout": "pool_timeout",
589 "recycle": "pool_recycle",
590 "events": "pool_events",
591 "reset_on_return": "pool_reset_on_return",
592 "pre_ping": "pool_pre_ping",
593 "use_lifo": "pool_use_lifo",
594 }
595 for k in util.get_cls_kwargs(poolclass):
596 tk = translate.get(k, k)
597 if tk in kwargs:
598 pool_args[k] = pop_kwarg(tk)
600 for plugin in plugins:
601 plugin.handle_pool_kwargs(poolclass, pool_args)
603 pool = poolclass(creator, **pool_args)
604 else:
605 if isinstance(pool, poollib.dbapi_proxy._DBProxy):
606 pool = pool.get_pool(*cargs, **cparams)
608 pool._dialect = dialect
610 # create engine.
611 if pop_kwarg("future", False):
612 from sqlalchemy import future
614 default_engine_class = future.Engine
615 else:
616 default_engine_class = base.Engine
618 engineclass = kwargs.pop("_future_engine_class", default_engine_class)
620 engine_args = {}
621 for k in util.get_cls_kwargs(engineclass):
622 if k in kwargs:
623 engine_args[k] = pop_kwarg(k)
625 # internal flags used by the test suite for instrumenting / proxying
626 # engines with mocks etc.
627 _initialize = kwargs.pop("_initialize", True)
628 _wrap_do_on_connect = kwargs.pop("_wrap_do_on_connect", None)
630 # all kwargs should be consumed
631 if kwargs:
632 raise TypeError(
633 "Invalid argument(s) %s sent to create_engine(), "
634 "using configuration %s/%s/%s. Please check that the "
635 "keyword arguments are appropriate for this combination "
636 "of components."
637 % (
638 ",".join("'%s'" % k for k in kwargs),
639 dialect.__class__.__name__,
640 pool.__class__.__name__,
641 engineclass.__name__,
642 )
643 )
645 engine = engineclass(pool, dialect, u, **engine_args)
647 if _initialize:
648 do_on_connect = dialect.on_connect_url(u)
649 if do_on_connect:
650 if _wrap_do_on_connect:
651 do_on_connect = _wrap_do_on_connect(do_on_connect)
653 def on_connect(dbapi_connection, connection_record):
654 do_on_connect(dbapi_connection)
656 event.listen(pool, "connect", on_connect)
658 def first_connect(dbapi_connection, connection_record):
659 c = base.Connection(
660 engine,
661 connection=dbapi_connection,
662 _has_events=False,
663 # reconnecting will be a reentrant condition, so if the
664 # connection goes away, Connection is then closed
665 _allow_revalidate=False,
666 )
667 c._execution_options = util.EMPTY_DICT
669 try:
670 dialect.initialize(c)
671 finally:
672 # note that "invalidated" and "closed" are mutually
673 # exclusive in 1.4 Connection.
674 if not c.invalidated and not c.closed:
675 # transaction is rolled back otherwise, tested by
676 # test/dialect/postgresql/test_dialect.py
677 # ::MiscBackendTest::test_initial_transaction_state
678 dialect.do_rollback(c.connection)
680 # previously, the "first_connect" event was used here, which was then
681 # scaled back if the "on_connect" handler were present. now,
682 # since "on_connect" is virtually always present, just use
683 # "connect" event with once_unless_exception in all cases so that
684 # the connection event flow is consistent in all cases.
685 event.listen(
686 pool, "connect", first_connect, _once_unless_exception=True
687 )
689 dialect_cls.engine_created(engine)
690 if entrypoint is not dialect_cls:
691 entrypoint.engine_created(engine)
693 for plugin in plugins:
694 plugin.engine_created(engine)
696 return engine
699def engine_from_config(configuration, prefix="sqlalchemy.", **kwargs):
700 """Create a new Engine instance using a configuration dictionary.
702 The dictionary is typically produced from a config file.
704 The keys of interest to ``engine_from_config()`` should be prefixed, e.g.
705 ``sqlalchemy.url``, ``sqlalchemy.echo``, etc. The 'prefix' argument
706 indicates the prefix to be searched for. Each matching key (after the
707 prefix is stripped) is treated as though it were the corresponding keyword
708 argument to a :func:`_sa.create_engine` call.
710 The only required key is (assuming the default prefix) ``sqlalchemy.url``,
711 which provides the :ref:`database URL <database_urls>`.
713 A select set of keyword arguments will be "coerced" to their
714 expected type based on string values. The set of arguments
715 is extensible per-dialect using the ``engine_config_types`` accessor.
717 :param configuration: A dictionary (typically produced from a config file,
718 but this is not a requirement). Items whose keys start with the value
719 of 'prefix' will have that prefix stripped, and will then be passed to
720 :func:`_sa.create_engine`.
722 :param prefix: Prefix to match and then strip from keys
723 in 'configuration'.
725 :param kwargs: Each keyword argument to ``engine_from_config()`` itself
726 overrides the corresponding item taken from the 'configuration'
727 dictionary. Keyword arguments should *not* be prefixed.
729 """
731 options = dict(
732 (key[len(prefix) :], configuration[key])
733 for key in configuration
734 if key.startswith(prefix)
735 )
736 options["_coerce_config"] = True
737 options.update(kwargs)
738 url = options.pop("url")
739 return create_engine(url, **options)