root/galaxy-central/eggs/SQLAlchemy-0.5.6_dev_r6498-py2.6.egg/sqlalchemy/interfaces.py

リビジョン 3, 5.5 KB (コミッタ: kohda, 14 年 前)

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1# interfaces.py
2# Copyright (C) 2007 Jason Kirtland jek@discorporate.us
3#
4# This module is part of SQLAlchemy and is released under
5# the MIT License: http://www.opensource.org/licenses/mit-license.php
6
7"""Interfaces and abstract types."""
8
9
10class PoolListener(object):
11    """Hooks into the lifecycle of connections in a ``Pool``.
12
13    Usage::
14   
15        class MyListener(PoolListener):
16            def connect(self, dbapi_con, con_record):
17                '''perform connect operations'''
18            # etc.
19           
20        # create a new pool with a listener
21        p = QueuePool(..., listeners=[MyListener()])
22       
23        # add a listener after the fact
24        p.add_listener(MyListener())
25       
26        # usage with create_engine()
27        e = create_engine("url://", listeners=[MyListener()])
28       
29    All of the standard connection :class:`~sqlalchemy.pool.Pool` types can
30    accept event listeners for key connection lifecycle events:
31    creation, pool check-out and check-in.  There are no events fired
32    when a connection closes.
33
34    For any given DB-API connection, there will be one ``connect``
35    event, `n` number of ``checkout`` events, and either `n` or `n - 1`
36    ``checkin`` events.  (If a ``Connection`` is detached from its
37    pool via the ``detach()`` method, it won't be checked back in.)
38
39    These are low-level events for low-level objects: raw Python
40    DB-API connections, without the conveniences of the SQLAlchemy
41    ``Connection`` wrapper, ``Dialect`` services or ``ClauseElement``
42    execution.  If you execute SQL through the connection, explicitly
43    closing all cursors and other resources is recommended.
44
45    Events also receive a ``_ConnectionRecord``, a long-lived internal
46    ``Pool`` object that basically represents a "slot" in the
47    connection pool.  ``_ConnectionRecord`` objects have one public
48    attribute of note: ``info``, a dictionary whose contents are
49    scoped to the lifetime of the DB-API connection managed by the
50    record.  You can use this shared storage area however you like.
51
52    There is no need to subclass ``PoolListener`` to handle events.
53    Any class that implements one or more of these methods can be used
54    as a pool listener.  The ``Pool`` will inspect the methods
55    provided by a listener object and add the listener to one or more
56    internal event queues based on its capabilities.  In terms of
57    efficiency and function call overhead, you're much better off only
58    providing implementations for the hooks you'll be using.
59   
60    """
61
62    def connect(self, dbapi_con, con_record):
63        """Called once for each new DB-API connection or Pool's ``creator()``.
64
65        dbapi_con
66          A newly connected raw DB-API connection (not a SQLAlchemy
67          ``Connection`` wrapper).
68
69        con_record
70          The ``_ConnectionRecord`` that persistently manages the connection
71
72        """
73
74    def checkout(self, dbapi_con, con_record, con_proxy):
75        """Called when a connection is retrieved from the Pool.
76
77        dbapi_con
78          A raw DB-API connection
79
80        con_record
81          The ``_ConnectionRecord`` that persistently manages the connection
82
83        con_proxy
84          The ``_ConnectionFairy`` which manages the connection for the span of
85          the current checkout.
86
87        If you raise an ``exc.DisconnectionError``, the current
88        connection will be disposed and a fresh connection retrieved.
89        Processing of all checkout listeners will abort and restart
90        using the new connection.
91        """
92
93    def checkin(self, dbapi_con, con_record):
94        """Called when a connection returns to the pool.
95
96        Note that the connection may be closed, and may be None if the
97        connection has been invalidated.  ``checkin`` will not be called
98        for detached connections.  (They do not return to the pool.)
99
100        dbapi_con
101          A raw DB-API connection
102
103        con_record
104          The ``_ConnectionRecord`` that persistently manages the connection
105
106        """
107
108class ConnectionProxy(object):
109    """Allows interception of statement execution by Connections.
110   
111    Either or both of the ``execute()`` and ``cursor_execute()``
112    may be implemented to intercept compiled statement and
113    cursor level executions, e.g.::
114   
115        class MyProxy(ConnectionProxy):
116            def execute(self, conn, execute, clauseelement, *multiparams, **params):
117                print "compiled statement:", clauseelement
118                return execute(clauseelement, *multiparams, **params)
119               
120            def cursor_execute(self, execute, cursor, statement, parameters, context, executemany):
121                print "raw statement:", statement
122                return execute(cursor, statement, parameters, context)
123
124    The ``execute`` argument is a function that will fulfill the default
125    execution behavior for the operation.  The signature illustrated
126    in the example should be used.
127   
128    The proxy is installed into an :class:`~sqlalchemy.engine.Engine` via
129    the ``proxy`` argument::
130   
131        e = create_engine('someurl://', proxy=MyProxy())
132   
133    """
134    def execute(self, conn, execute, clauseelement, *multiparams, **params):
135        """Intercept high level execute() events."""
136       
137        return execute(clauseelement, *multiparams, **params)
138
139    def cursor_execute(self, execute, cursor, statement, parameters, context, executemany):
140        """Intercept low-level cursor execute() events."""
141       
142        return execute(cursor, statement, parameters, context)
143
144       
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