# engine/__init__.py
# Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Michael Bayer mike_mp@zzzcomputing.com
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""SQL connections, SQL execution and high-level DB-API interface.
The engine package defines the basic components used to interface
DB-API modules with higher-level statement construction,
connection-management, execution and result contexts. The primary
"entry point" class into this package is the Engine and it's public
constructor ``create_engine()``.
This package includes:
base.py
Defines interface classes and some implementation classes which
comprise the basic components used to interface between a DB-API,
constructed and plain-text statements, connections, transactions,
and results.
default.py
Contains default implementations of some of the components defined
in base.py. All current database dialects use the classes in
default.py as base classes for their own database-specific
implementations.
strategies.py
The mechanics of constructing ``Engine`` objects are represented
here. Defines the ``EngineStrategy`` class which represents how
to go from arguments specified to the ``create_engine()``
function, to a fully constructed ``Engine``, including
initialization of connection pooling, dialects, and specific
subclasses of ``Engine``.
threadlocal.py
The ``TLEngine`` class is defined here, which is a subclass of
the generic ``Engine`` and tracks ``Connection`` and
``Transaction`` objects against the identity of the current
thread. This allows certain programming patterns based around
the concept of a "thread-local connection" to be possible.
The ``TLEngine`` is created by using the "threadlocal" engine
strategy in conjunction with the ``create_engine()`` function.
url.py
Defines the ``URL`` class which represents the individual
components of a string URL passed to ``create_engine()``. Also
defines a basic module-loading strategy for the dialect specifier
within a URL.
"""
# not sure what this was used for
#import sqlalchemy.databases
from sqlalchemy.engine.base import (
BufferedColumnResultProxy,
BufferedColumnRow,
BufferedRowResultProxy,
Compiled,
Connectable,
Connection,
Dialect,
Engine,
ExecutionContext,
NestedTransaction,
ResultProxy,
RootTransaction,
RowProxy,
Transaction,
TwoPhaseTransaction,
TypeCompiler
)
from sqlalchemy.engine import strategies
from sqlalchemy import util
__all__ = (
'BufferedColumnResultProxy',
'BufferedColumnRow',
'BufferedRowResultProxy',
'Compiled',
'Connectable',
'Connection',
'Dialect',
'Engine',
'ExecutionContext',
'NestedTransaction',
'ResultProxy',
'RootTransaction',
'RowProxy',
'Transaction',
'TwoPhaseTransaction',
'TypeCompiler',
'create_engine',
'engine_from_config',
)
default_strategy = 'plain'
def create_engine(*args, **kwargs):
"""Create a new Engine instance.
The standard method of specifying the engine is via URL as the
first positional argument, to indicate the appropriate database
dialect and connection arguments, with additional keyword
arguments sent as options to the dialect and resulting Engine.
The URL is a string in the form
``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 Engine, the underlying Dialect, as well as the
Pool. Specific dialects also accept keyword arguments that
are unique to that dialect. Here, we describe the parameters
that are common to most ``create_engine()`` usage.
:param assert_unicode: Deprecated. A warning is raised in all cases when a non-Unicode
object is passed when SQLAlchemy would coerce into an encoding
(note: but **not** when the DBAPI handles unicode objects natively).
To suppress or raise this warning to an
error, use the Python warnings filter documented at:
http://docs.python.org/library/warnings.html
:param connect_args: a dictionary of options which will be
passed directly to the DBAPI's ``connect()`` method as
additional keyword arguments.
:param convert_unicode=False: if set to True, all
String/character based types will convert Unicode values to raw
byte values going into the database, and all raw byte values to
Python Unicode coming out in result sets. This is an
engine-wide method to provide unicode conversion across the
board. For unicode conversion on a column-by-column level, use
the ``Unicode`` column type instead, described in `types`.
: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.
:param echo=False: if True, the Engine will log all statements
as well as a repr() of their parameter lists to the engines
logger, which defaults to sys.stdout. The ``echo`` attribute of
``Engine`` can be modified at any time to turn logging on and
off. If set to the string ``"debug"``, result rows will be
printed to the standard output as well. This flag ultimately
controls a Python logger; see :ref:`dbengine_logging` for
information on how to configure logging directly.
:param echo_pool=False: if True, the connection pool will log
all checkouts/checkins to the logging stream, which defaults to
sys.stdout. This flag ultimately controls a Python logger; see
:ref:`dbengine_logging` for information on how to configure logging
directly.
:param encoding='utf-8': the encoding to use for all Unicode
translations, both by engine-wide unicode conversion as well as
the ``Unicode`` type object.
: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`` is used instead.
:param listeners: A list of one or more
:class:`~sqlalchemy.interfaces.PoolListener` objects which will
receive connection pool events.
: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.
: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: used by database implementations which
support multiple DBAPI modules, this is a reference to a DBAPI2
module to be used instead of the engine's default module. For
PostgreSQL, the default is psycopg2. For Oracle, it's cx_Oracle.
: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 `pooling`.
: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.
: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`.
: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).
: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`.
:param strategy='plain': used to invoke alternate :class:`~sqlalchemy.engine.base.Engine.`
implementations. Currently available is the ``threadlocal``
strategy, which is described in :ref:`threadlocal_strategy`.
"""
strategy = kwargs.pop('strategy', default_strategy)
strategy = strategies.strategies[strategy]
return strategy.create(*args, **kwargs)
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 where keys
are prefixed, such as sqlalchemy.url, sqlalchemy.echo, etc. The
'prefix' argument indicates the prefix to be searched for.
A select set of keyword arguments will be "coerced" to their
expected type based on string values. In a future release, this
functionality will be expanded and include dialect-specific
arguments.
"""
opts = _coerce_config(configuration, prefix)
opts.update(kwargs)
url = opts.pop('url')
return create_engine(url, **opts)
def _coerce_config(configuration, prefix):
"""Convert configuration values to expected types."""
options = dict((key[len(prefix):], configuration[key])
for key in configuration
if key.startswith(prefix))
for option, type_ in (
('convert_unicode', bool),
('pool_timeout', int),
('echo', bool),
('echo_pool', bool),
('pool_recycle', int),
('pool_size', int),
('max_overflow', int),
('pool_threadlocal', bool),
):
util.coerce_kw_type(options, option, type_)
return options
|