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Edit File: create.py
# engine/create.py # Copyright (C) 2005-2024 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: https://www.opensource.org/licenses/mit-license.php from . import base from . import url as _url from .mock import create_mock_engine from .. import event from .. import exc from .. import pool as poollib from .. import util from ..sql import compiler @util.deprecated_params( strategy=( "1.4", "The :paramref:`_sa.create_engine.strategy` keyword is deprecated, " "and the only argument accepted is 'mock'; please use " ":func:`.create_mock_engine` going forward. For general " "customization of create_engine which may have been accomplished " "using strategies, see :class:`.CreateEnginePlugin`.", ), empty_in_strategy=( "1.4", "The :paramref:`_sa.create_engine.empty_in_strategy` keyword is " "deprecated, and no longer has any effect. All IN expressions " "are now rendered using " 'the "expanding parameter" strategy which renders a set of bound' 'expressions, or an "empty set" SELECT, at statement execution' "time.", ), case_sensitive=( "1.4", "The :paramref:`_sa.create_engine.case_sensitive` parameter " "is deprecated and will be removed in a future release. " "Applications should work with result column names in a case " "sensitive fashion.", ), ) def create_engine(url, **kwargs): """Create a new :class:`_engine.Engine` instance. The standard calling form is to send the :ref:`URL <database_urls>` as the first positional argument, usually a string that indicates database dialect and connection arguments:: engine = create_engine("postgresql://scott:tiger@localhost/test") .. note:: Please review :ref:`database_urls` for general guidelines in composing URL strings. In particular, special characters, such as those often part of passwords, must be URL encoded to be properly parsed. Additional keyword arguments may then follow it which establish various options on the resulting :class:`_engine.Engine` and its underlying :class:`.Dialect` and :class:`_pool.Pool` constructs:: engine = create_engine("mysql://scott:tiger@hostname/dbname", encoding='latin1', echo=True) The string form of the URL is ``dialect[+driver]://user:password@host/dbname[?key=value..]``, where ``dialect`` is a database name such as ``mysql``, ``oracle``, ``postgresql``, etc., and ``driver`` the name of a DBAPI, such as ``psycopg2``, ``pyodbc``, ``cx_oracle``, etc. Alternatively, the URL can be an instance of :class:`~sqlalchemy.engine.url.URL`. ``**kwargs`` takes a wide variety of options which are routed towards their appropriate components. Arguments may be specific to the :class:`_engine.Engine`, the underlying :class:`.Dialect`, as well as the :class:`_pool.Pool`. Specific dialects also accept keyword arguments that are unique to that dialect. Here, we describe the parameters that are common to most :func:`_sa.create_engine()` usage. Once established, the newly resulting :class:`_engine.Engine` will request a connection from the underlying :class:`_pool.Pool` once :meth:`_engine.Engine.connect` is called, or a method which depends on it such as :meth:`_engine.Engine.execute` is invoked. The :class:`_pool.Pool` in turn will establish the first actual DBAPI connection when this request is received. The :func:`_sa.create_engine` call itself does **not** establish any actual DBAPI connections directly. .. seealso:: :doc:`/core/engines` :doc:`/dialects/index` :ref:`connections_toplevel` :param case_sensitive: if False, result column names will match in a case-insensitive fashion, that is, ``row['SomeColumn']``. :param connect_args: a dictionary of options which will be passed directly to the DBAPI's ``connect()`` method as additional keyword arguments. See the example at :ref:`custom_dbapi_args`. :param convert_unicode=False: if set to True, causes all :class:`.String` datatypes to act as though the :paramref:`.String.convert_unicode` flag has been set to ``True``, regardless of a setting of ``False`` on an individual :class:`.String` type. This has the effect of causing all :class:`.String` -based columns to accommodate Python Unicode objects directly as though the datatype were the :class:`.Unicode` type. .. deprecated:: 1.3 The :paramref:`_sa.create_engine.convert_unicode` parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary. :param creator: a callable which returns a DBAPI connection. This creation function will be passed to the underlying connection pool and will be used to create all new database connections. Usage of this function causes connection parameters specified in the URL argument to be bypassed. This hook is not as flexible as the newer :meth:`_events.DialectEvents.do_connect` hook which allows complete control over how a connection is made to the database, given the full set of URL arguments and state beforehand. .. seealso:: :meth:`_events.DialectEvents.do_connect` - event hook that allows full control over DBAPI connection mechanics. :ref:`custom_dbapi_args` :param echo=False: if True, the Engine will log all statements as well as a ``repr()`` of their parameter lists to the default log handler, which defaults to ``sys.stdout`` for output. If set to the string ``"debug"``, result rows will be printed to the standard output as well. The ``echo`` attribute of ``Engine`` can be modified at any time to turn logging on and off; direct control of logging is also available using the standard Python ``logging`` module. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param echo_pool=False: if True, the connection pool will log informational output such as when connections are invalidated as well as when connections are recycled to the default log handler, which defaults to ``sys.stdout`` for output. If set to the string ``"debug"``, the logging will include pool checkouts and checkins. Direct control of logging is also available using the standard Python ``logging`` module. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param empty_in_strategy: No longer used; SQLAlchemy now uses "empty set" behavior for IN in all cases. :param enable_from_linting: defaults to True. Will emit a warning if a given SELECT statement is found to have un-linked FROM elements which would cause a cartesian product. .. versionadded:: 1.4 .. seealso:: :ref:`change_4737` :param encoding: **legacy Python 2 value only, where it only applies to specific DBAPIs, not used in Python 3 for any modern DBAPI driver. Please refer to individual dialect documentation for client encoding behaviors.** Defaults to the string value ``utf-8``. This value refers **only** to the character encoding that is used when SQLAlchemy sends or receives data from a :term:`DBAPI` that does not support Python Unicode and **is only used under Python 2**, only for certain DBAPI drivers, and only in certain circumstances. **Python 3 users please DISREGARD this parameter and refer to the documentation for the specific dialect in use in order to configure character encoding behavior.** .. note:: The ``encoding`` parameter deals only with in-Python encoding issues that were prevalent with **some DBAPIS only** under **Python 2 only**. Under Python 3 it is not used by any modern dialect. For DBAPIs that require client encoding configurations, which are most of those outside of SQLite, please consult specific :ref:`dialect documentation <dialect_toplevel>` for details. All modern DBAPIs that work in Python 3 necessarily feature direct support for Python unicode strings. Under Python 2, this was not always the case. For those scenarios where the DBAPI is detected as not supporting a Python ``unicode`` object under Python 2, this encoding is used to determine the source/destination encoding. It is **not used** for those cases where the DBAPI handles unicode directly. To properly configure a system to accommodate Python ``unicode`` objects, the DBAPI should be configured to handle unicode to the greatest degree as is appropriate - see the notes on unicode pertaining to the specific target database in use at :ref:`dialect_toplevel`. Areas where string encoding may need to be accommodated outside of the DBAPI, nearly always under **Python 2 only**, include zero or more of: * the values passed to bound parameters, corresponding to the :class:`.Unicode` type or the :class:`.String` type when ``convert_unicode`` is ``True``; * the values returned in result set columns corresponding to the :class:`.Unicode` type or the :class:`.String` type when ``convert_unicode`` is ``True``; * the string SQL statement passed to the DBAPI's ``cursor.execute()`` method; * the string names of the keys in the bound parameter dictionary passed to the DBAPI's ``cursor.execute()`` as well as ``cursor.setinputsizes()`` methods; * the string column names retrieved from the DBAPI's ``cursor.description`` attribute. When using Python 3, the DBAPI is required to support all of the above values as Python ``unicode`` objects, which in Python 3 are just known as ``str``. In Python 2, the DBAPI does not specify unicode behavior at all, so SQLAlchemy must make decisions for each of the above values on a per-DBAPI basis - implementations are completely inconsistent in their behavior. :param execution_options: Dictionary execution options which will be applied to all connections. See :meth:`~sqlalchemy.engine.Connection.execution_options` :param future: Use the 2.0 style :class:`_future.Engine` and :class:`_future.Connection` API. .. versionadded:: 1.4 .. seealso:: :ref:`migration_20_toplevel` :param hide_parameters: Boolean, when set to True, SQL statement parameters will not be displayed in INFO logging nor will they be formatted into the string representation of :class:`.StatementError` objects. .. versionadded:: 1.3.8 .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param implicit_returning=True: Legacy flag that when set to ``False`` will disable the use of ``RETURNING`` on supporting backends where it would normally be used to fetch newly generated primary key values for single-row INSERT statements that do not otherwise specify a RETURNING clause. This behavior applies primarily to the PostgreSQL, Oracle, SQL Server backends. .. warning:: this flag originally allowed the "implicit returning" feature to be *enabled* back when it was very new and there was not well-established database support. In modern SQLAlchemy, this flag should **always be set to True**. Some SQLAlchemy features will fail to function properly if this flag is set to ``False``. :param isolation_level: this string parameter is interpreted by various dialects in order to affect the transaction isolation level of the database connection. The parameter essentially accepts some subset of these string arguments: ``"SERIALIZABLE"``, ``"REPEATABLE READ"``, ``"READ COMMITTED"``, ``"READ UNCOMMITTED"`` and ``"AUTOCOMMIT"``. Behavior here varies per backend, and individual dialects should be consulted directly. Note that the isolation level can also be set on a per-:class:`_engine.Connection` basis as well, using the :paramref:`.Connection.execution_options.isolation_level` feature. .. seealso:: :ref:`dbapi_autocommit` :param json_deserializer: for dialects that support the :class:`_types.JSON` datatype, this is a Python callable that will convert a JSON string to a Python object. By default, the Python ``json.loads`` function is used. .. versionchanged:: 1.3.7 The SQLite dialect renamed this from ``_json_deserializer``. :param json_serializer: for dialects that support the :class:`_types.JSON` datatype, this is a Python callable that will render a given object as JSON. By default, the Python ``json.dumps`` function is used. .. versionchanged:: 1.3.7 The SQLite dialect renamed this from ``_json_serializer``. :param label_length=None: optional integer value which limits the size of dynamically generated column labels to that many characters. If less than 6, labels are generated as "_(counter)". If ``None``, the value of ``dialect.max_identifier_length``, which may be affected via the :paramref:`_sa.create_engine.max_identifier_length` parameter, is used instead. The value of :paramref:`_sa.create_engine.label_length` may not be larger than that of :paramref:`_sa.create_engine.max_identfier_length`. .. seealso:: :paramref:`_sa.create_engine.max_identifier_length` :param logging_name: String identifier which will be used within the "name" field of logging records generated within the "sqlalchemy.engine" logger. Defaults to a hexstring of the object's id. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :paramref:`_engine.Connection.execution_options.logging_token` :param max_identifier_length: integer; override the max_identifier_length determined by the dialect. if ``None`` or zero, has no effect. This is the database's configured maximum number of characters that may be used in a SQL identifier such as a table name, column name, or label name. All dialects determine this value automatically, however in the case of a new database version for which this value has changed but SQLAlchemy's dialect has not been adjusted, the value may be passed here. .. versionadded:: 1.3.9 .. seealso:: :paramref:`_sa.create_engine.label_length` :param max_overflow=10: the number of connections to allow in connection pool "overflow", that is connections that can be opened above and beyond the pool_size setting, which defaults to five. this is only used with :class:`~sqlalchemy.pool.QueuePool`. :param module=None: reference to a Python module object (the module itself, not its string name). Specifies an alternate DBAPI module to be used by the engine's dialect. Each sub-dialect references a specific DBAPI which will be imported before first connect. This parameter causes the import to be bypassed, and the given module to be used instead. Can be used for testing of DBAPIs as well as to inject "mock" DBAPI implementations into the :class:`_engine.Engine`. :param paramstyle=None: The `paramstyle <https://legacy.python.org/dev/peps/pep-0249/#paramstyle>`_ to use when rendering bound parameters. This style defaults to the one recommended by the DBAPI itself, which is retrieved from the ``.paramstyle`` attribute of the DBAPI. However, most DBAPIs accept more than one paramstyle, and in particular it may be desirable to change a "named" paramstyle into a "positional" one, or vice versa. When this attribute is passed, it should be one of the values ``"qmark"``, ``"numeric"``, ``"named"``, ``"format"`` or ``"pyformat"``, and should correspond to a parameter style known to be supported by the DBAPI in use. :param pool=None: an already-constructed instance of :class:`~sqlalchemy.pool.Pool`, such as a :class:`~sqlalchemy.pool.QueuePool` instance. If non-None, this pool will be used directly as the underlying connection pool for the engine, bypassing whatever connection parameters are present in the URL argument. For information on constructing connection pools manually, see :ref:`pooling_toplevel`. :param poolclass=None: a :class:`~sqlalchemy.pool.Pool` subclass, which will be used to create a connection pool instance using the connection parameters given in the URL. Note this differs from ``pool`` in that you don't actually instantiate the pool in this case, you just indicate what type of pool to be used. :param pool_logging_name: String identifier which will be used within the "name" field of logging records generated within the "sqlalchemy.pool" logger. Defaults to a hexstring of the object's id. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param pool_pre_ping: boolean, if True will enable the connection pool "pre-ping" feature that tests connections for liveness upon each checkout. .. versionadded:: 1.2 .. seealso:: :ref:`pool_disconnects_pessimistic` :param pool_size=5: the number of connections to keep open inside the connection pool. This used with :class:`~sqlalchemy.pool.QueuePool` as well as :class:`~sqlalchemy.pool.SingletonThreadPool`. With :class:`~sqlalchemy.pool.QueuePool`, a ``pool_size`` setting of 0 indicates no limit; to disable pooling, set ``poolclass`` to :class:`~sqlalchemy.pool.NullPool` instead. :param pool_recycle=-1: this setting causes the pool to recycle connections after the given number of seconds has passed. It defaults to -1, or no timeout. For example, setting to 3600 means connections will be recycled after one hour. Note that MySQL in particular will disconnect automatically if no activity is detected on a connection for eight hours (although this is configurable with the MySQLDB connection itself and the server configuration as well). .. seealso:: :ref:`pool_setting_recycle` :param pool_reset_on_return='rollback': set the :paramref:`_pool.Pool.reset_on_return` parameter of the underlying :class:`_pool.Pool` object, which can be set to the values ``"rollback"``, ``"commit"``, or ``None``. .. seealso:: :ref:`pool_reset_on_return` :param pool_timeout=30: number of seconds to wait before giving up on getting a connection from the pool. This is only used with :class:`~sqlalchemy.pool.QueuePool`. This can be a float but is subject to the limitations of Python time functions which may not be reliable in the tens of milliseconds. .. note: don't use 30.0 above, it seems to break with the :param tag :param pool_use_lifo=False: use LIFO (last-in-first-out) when retrieving connections from :class:`.QueuePool` instead of FIFO (first-in-first-out). Using LIFO, a server-side timeout scheme can reduce the number of connections used during non- peak periods of use. When planning for server-side timeouts, ensure that a recycle or pre-ping strategy is in use to gracefully handle stale connections. .. versionadded:: 1.3 .. seealso:: :ref:`pool_use_lifo` :ref:`pool_disconnects` :param plugins: string list of plugin names to load. See :class:`.CreateEnginePlugin` for background. .. versionadded:: 1.2.3 :param query_cache_size: size of the cache used to cache the SQL string form of queries. Set to zero to disable caching. The cache is pruned of its least recently used items when its size reaches N * 1.5. Defaults to 500, meaning the cache will always store at least 500 SQL statements when filled, and will grow up to 750 items at which point it is pruned back down to 500 by removing the 250 least recently used items. Caching is accomplished on a per-statement basis by generating a cache key that represents the statement's structure, then generating string SQL for the current dialect only if that key is not present in the cache. All statements support caching, however some features such as an INSERT with a large set of parameters will intentionally bypass the cache. SQL logging will indicate statistics for each statement whether or not it were pull from the cache. .. note:: some ORM functions related to unit-of-work persistence as well as some attribute loading strategies will make use of individual per-mapper caches outside of the main cache. .. seealso:: :ref:`sql_caching` .. versionadded:: 1.4 """ # noqa if "strategy" in kwargs: strat = kwargs.pop("strategy") if strat == "mock": return create_mock_engine(url, **kwargs) else: raise exc.ArgumentError("unknown strategy: %r" % strat) kwargs.pop("empty_in_strategy", None) # create url.URL object u = _url.make_url(url) u, plugins, kwargs = u._instantiate_plugins(kwargs) entrypoint = u._get_entrypoint() dialect_cls = entrypoint.get_dialect_cls(u) if kwargs.pop("_coerce_config", False): def pop_kwarg(key, default=None): value = kwargs.pop(key, default) if key in dialect_cls.engine_config_types: value = dialect_cls.engine_config_types[key](value) return value else: pop_kwarg = kwargs.pop dialect_args = {} # consume dialect arguments from kwargs for k in util.get_cls_kwargs(dialect_cls): if k in kwargs: dialect_args[k] = pop_kwarg(k) dbapi = kwargs.pop("module", None) if dbapi is None: dbapi_args = {} for k in util.get_func_kwargs(dialect_cls.dbapi): if k in kwargs: dbapi_args[k] = pop_kwarg(k) dbapi = dialect_cls.dbapi(**dbapi_args) dialect_args["dbapi"] = dbapi dialect_args.setdefault("compiler_linting", compiler.NO_LINTING) enable_from_linting = kwargs.pop("enable_from_linting", True) if enable_from_linting: dialect_args["compiler_linting"] ^= compiler.COLLECT_CARTESIAN_PRODUCTS for plugin in plugins: plugin.handle_dialect_kwargs(dialect_cls, dialect_args) # create dialect dialect = dialect_cls(**dialect_args) # assemble connection arguments (cargs, cparams) = dialect.create_connect_args(u) cparams.update(pop_kwarg("connect_args", {})) cargs = list(cargs) # allow mutability # look for existing pool or create pool = pop_kwarg("pool", None) if pool is None: def connect(connection_record=None): if dialect._has_events: for fn in dialect.dispatch.do_connect: connection = fn(dialect, connection_record, cargs, cparams) if connection is not None: return connection return dialect.connect(*cargs, **cparams) creator = pop_kwarg("creator", connect) poolclass = pop_kwarg("poolclass", None) if poolclass is None: poolclass = dialect.get_dialect_pool_class(u) pool_args = {"dialect": dialect} # consume pool arguments from kwargs, translating a few of # the arguments translate = { "logging_name": "pool_logging_name", "echo": "echo_pool", "timeout": "pool_timeout", "recycle": "pool_recycle", "events": "pool_events", "reset_on_return": "pool_reset_on_return", "pre_ping": "pool_pre_ping", "use_lifo": "pool_use_lifo", } for k in util.get_cls_kwargs(poolclass): tk = translate.get(k, k) if tk in kwargs: pool_args[k] = pop_kwarg(tk) for plugin in plugins: plugin.handle_pool_kwargs(poolclass, pool_args) pool = poolclass(creator, **pool_args) else: if isinstance(pool, poollib.dbapi_proxy._DBProxy): pool = pool.get_pool(*cargs, **cparams) pool._dialect = dialect # create engine. if pop_kwarg("future", False): from sqlalchemy import future default_engine_class = future.Engine else: default_engine_class = base.Engine engineclass = kwargs.pop("_future_engine_class", default_engine_class) engine_args = {} for k in util.get_cls_kwargs(engineclass): if k in kwargs: engine_args[k] = pop_kwarg(k) # internal flags used by the test suite for instrumenting / proxying # engines with mocks etc. _initialize = kwargs.pop("_initialize", True) _wrap_do_on_connect = kwargs.pop("_wrap_do_on_connect", None) # all kwargs should be consumed if kwargs: raise TypeError( "Invalid argument(s) %s sent to create_engine(), " "using configuration %s/%s/%s. Please check that the " "keyword arguments are appropriate for this combination " "of components." % ( ",".join("'%s'" % k for k in kwargs), dialect.__class__.__name__, pool.__class__.__name__, engineclass.__name__, ) ) engine = engineclass(pool, dialect, u, **engine_args) if _initialize: do_on_connect = dialect.on_connect_url(u) if do_on_connect: if _wrap_do_on_connect: do_on_connect = _wrap_do_on_connect(do_on_connect) def on_connect(dbapi_connection, connection_record): do_on_connect(dbapi_connection) event.listen(pool, "connect", on_connect) def first_connect(dbapi_connection, connection_record): c = base.Connection( engine, connection=dbapi_connection, _has_events=False, # reconnecting will be a reentrant condition, so if the # connection goes away, Connection is then closed _allow_revalidate=False, ) c._execution_options = util.EMPTY_DICT try: dialect.initialize(c) finally: # note that "invalidated" and "closed" are mutually # exclusive in 1.4 Connection. if not c.invalidated and not c.closed: # transaction is rolled back otherwise, tested by # test/dialect/postgresql/test_dialect.py # ::MiscBackendTest::test_initial_transaction_state dialect.do_rollback(c.connection) # previously, the "first_connect" event was used here, which was then # scaled back if the "on_connect" handler were present. now, # since "on_connect" is virtually always present, just use # "connect" event with once_unless_exception in all cases so that # the connection event flow is consistent in all cases. event.listen( pool, "connect", first_connect, _once_unless_exception=True ) dialect_cls.engine_created(engine) if entrypoint is not dialect_cls: entrypoint.engine_created(engine) for plugin in plugins: plugin.engine_created(engine) return engine def engine_from_config(configuration, prefix="sqlalchemy.", **kwargs): """Create a new Engine instance using a configuration dictionary. The dictionary is typically produced from a config file. The keys of interest to ``engine_from_config()`` should be prefixed, e.g. ``sqlalchemy.url``, ``sqlalchemy.echo``, etc. The 'prefix' argument indicates the prefix to be searched for. Each matching key (after the prefix is stripped) is treated as though it were the corresponding keyword argument to a :func:`_sa.create_engine` call. The only required key is (assuming the default prefix) ``sqlalchemy.url``, which provides the :ref:`database URL <database_urls>`. A select set of keyword arguments will be "coerced" to their expected type based on string values. The set of arguments is extensible per-dialect using the ``engine_config_types`` accessor. :param configuration: A dictionary (typically produced from a config file, but this is not a requirement). Items whose keys start with the value of 'prefix' will have that prefix stripped, and will then be passed to :func:`_sa.create_engine`. :param prefix: Prefix to match and then strip from keys in 'configuration'. :param kwargs: Each keyword argument to ``engine_from_config()`` itself overrides the corresponding item taken from the 'configuration' dictionary. Keyword arguments should *not* be prefixed. """ options = dict( (key[len(prefix) :], configuration[key]) for key in configuration if key.startswith(prefix) ) options["_coerce_config"] = True options.update(kwargs) url = options.pop("url") return create_engine(url, **options)