Edit File: strategies.py
# engine/strategies.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 """Strategies for creating new instances of Engine types. These are semi-private implementation classes which provide the underlying behavior for the "strategy" keyword argument available on :func:`~sqlalchemy.engine.create_engine`. Current available options are ``plain``, ``threadlocal``, and ``mock``. New strategies can be added via new ``EngineStrategy`` classes. """ from operator import attrgetter from . import base from . import threadlocal from . import url from .. import event from .. import pool as poollib from .. import util from ..sql import schema strategies = {} class EngineStrategy(object): """An adaptor that processes input arguments and produces an Engine. Provides a ``create`` method that receives input arguments and produces an instance of base.Engine or a subclass. """ def __init__(self): strategies[self.name] = self def create(self, *args, **kwargs): """Given arguments, returns a new Engine instance.""" raise NotImplementedError() class DefaultEngineStrategy(EngineStrategy): """Base class for built-in strategies.""" def create(self, name_or_url, **kwargs): # create url.URL object u = url.make_url(name_or_url) plugins = u._instantiate_plugins(kwargs) u.query.pop("plugin", None) kwargs.pop("plugins", None) 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 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_cls.get_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", "use_threadlocal": "pool_threadlocal", "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) else: pool = pool pool._dialect = dialect # create engine. engineclass = self.engine_cls engine_args = {} for k in util.get_cls_kwargs(engineclass): if k in kwargs: engine_args[k] = pop_kwarg(k) _initialize = kwargs.pop("_initialize", True) # 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() if do_on_connect: def on_connect(dbapi_connection, connection_record): conn = getattr( dbapi_connection, "_sqla_unwrap", dbapi_connection ) if conn is None: return do_on_connect(conn) event.listen(pool, "first_connect", on_connect) event.listen(pool, "connect", on_connect) def first_connect(dbapi_connection, connection_record): c = base.Connection( engine, connection=dbapi_connection, _has_events=False ) c._execution_options = util.immutabledict() dialect.initialize(c) dialect.do_rollback(c.connection) event.listen( pool, "first_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 class PlainEngineStrategy(DefaultEngineStrategy): """Strategy for configuring a regular Engine.""" name = "plain" engine_cls = base.Engine PlainEngineStrategy() class ThreadLocalEngineStrategy(DefaultEngineStrategy): """Strategy for configuring an Engine with threadlocal behavior.""" name = "threadlocal" engine_cls = threadlocal.TLEngine ThreadLocalEngineStrategy() class MockEngineStrategy(EngineStrategy): """Strategy for configuring an Engine-like object with mocked execution. Produces a single mock Connectable object which dispatches statement execution to a passed-in function. """ name = "mock" def create(self, name_or_url, executor, **kwargs): # create url.URL object u = url.make_url(name_or_url) dialect_cls = u.get_dialect() dialect_args = {} # consume dialect arguments from kwargs for k in util.get_cls_kwargs(dialect_cls): if k in kwargs: dialect_args[k] = kwargs.pop(k) # create dialect dialect = dialect_cls(**dialect_args) return MockEngineStrategy.MockConnection(dialect, executor) class MockConnection(base.Connectable): def __init__(self, dialect, execute): self._dialect = dialect self.execute = execute engine = property(lambda s: s) dialect = property(attrgetter("_dialect")) name = property(lambda s: s._dialect.name) schema_for_object = schema._schema_getter(None) def contextual_connect(self, **kwargs): return self def connect(self, **kwargs): return self def execution_options(self, **kw): return self def compiler(self, statement, parameters, **kwargs): return self._dialect.compiler( statement, parameters, engine=self, **kwargs ) def create(self, entity, **kwargs): kwargs["checkfirst"] = False from sqlalchemy.engine import ddl ddl.SchemaGenerator(self.dialect, self, **kwargs).traverse_single( entity ) def drop(self, entity, **kwargs): kwargs["checkfirst"] = False from sqlalchemy.engine import ddl ddl.SchemaDropper(self.dialect, self, **kwargs).traverse_single( entity ) def _run_visitor( self, visitorcallable, element, connection=None, **kwargs ): kwargs["checkfirst"] = False visitorcallable(self.dialect, self, **kwargs).traverse_single( element ) def execute(self, object_, *multiparams, **params): raise NotImplementedError() MockEngineStrategy()