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155 lines
4.6 KiB
ReStructuredText
155 lines
4.6 KiB
ReStructuredText
:mod:`psycopg2.extensions` -- Extensions to the DBAPI
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=====================================================
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.. sectionauthor:: Daniele Varrazzo <daniele.varrazzo@gmail.com>
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.. module:: psycopg2.extensions
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The module contains a few objects and function extending the minimum set of
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functionalities defined by the |DBAPI 2.0|.
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.. class:: connection
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Is the class usually returned by the :func:`psycopg2.connect()` function.
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It is exposed by the :mod:`extensions` module in order to allow
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subclassing to extend its behaviour: the subclass should be passed to the
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:func:`connect()` function using the :obj:`connection_factory` parameter.
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See also :ref:`subclassing-connection`.
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For a complete description of the class, see :class:`connection`.
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.. class:: cursor
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It is the class usually returnded by the :meth:`connection.cursor()`
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method. It is exposed by the :mod:`extensions` module in order to allow
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subclassing to extend its behaviour: the subclass should be passed to the
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``cursor()`` method using the :obj:`cursor_factory` parameter. See
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also :ref:`subclassing-cursor`.
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For a complete description of the class, see :class:`cursor`.
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.. todo:: row factories
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.. class:: lobject
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.. todo:: class lobject
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.. todo:: finish module extensions
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.. _isolation-level-constants:
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Isolation level constants
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-------------------------
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Psycopg2 connection objects hold informations about the PostgreSQL
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`transaction isolation level`_. The current transaction level can be read
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from the :attr:`connection.isolation_level` attribute. The default isolation
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level is ``READ COMMITTED``. A different isolation level con be set through
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the :meth:`connection.set_isolation_level()` method. The level can be set to
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one of the following constants:
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.. data:: ISOLATION_LEVEL_AUTOCOMMIT
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No transaction is started when command are issued and no ``commit()`` or
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``rollback()`` is required. Some PostgreSQL command such as ``CREATE
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DATABASE`` can't run into a transaction: to run such command use::
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>>> conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)
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.. data:: ISOLATION_LEVEL_READ_UNCOMMITTED
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This isolation level is defined in the SQL standard but not available in
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the MVCC model of PostgreSQL: it is replaced by the stricter ``READ
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COMMITTED``.
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.. data:: ISOLATION_LEVEL_READ_COMMITTED
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This is the default value. A new transaction is started at the first
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:meth:`cursor.execute()` command on a cursor and at each new ``execute()``
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after a :meth:`connection.commit()` or a :meth:`connection.rollback()`.
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The transaction runs in the PostgreSQL ``READ COMMITTED`` isolation level.
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.. data:: ISOLATION_LEVEL_REPEATABLE_READ
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This isolation level is defined in the SQL standard but not available in
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the MVCC model of PostgreSQL: it is replaced by the stricter
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``SERIALIZABLE``.
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.. data:: ISOLATION_LEVEL_SERIALIZABLE
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Transactions are run at a ``SERIALIZABLE`` isolation level. This is the
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strictest transactions isolation level, equivalent to having the
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transactions executed serially rather than concurrently. However
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applications using this level must be prepared to retry reansactions due
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to serialization failures. See `serializable isolation level`_ in
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PostgreSQL documentation.
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.. _transaction-status-constants:
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Transaction status constants
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----------------------------
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These values represent the possible status of a transaction: the current value
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can be read using the :meth:`connection.get_transaction_status()` method.
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.. data:: TRANSACTION_STATUS_IDLE
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The session is idle and there is no current transaction.
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.. data:: TRANSACTION_STATUS_ACTIVE
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A command is currently in progress.
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.. data:: TRANSACTION_STATUS_INTRANS
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The session is idle in a valid transaction block.
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.. data:: TRANSACTION_STATUS_INERROR
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The session is idle in a failed transaction block.
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.. data:: TRANSACTION_STATUS_UNKNOWN
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Reported if the connection with the server is bad.
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.. _connection-status-constants:
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Connection status constants
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---------------------------
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These values represent the possible status of a connection: the current value
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can be read from the :data:`connection.status` attribute.
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.. todo:: check if these values are really useful or not.
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.. data:: STATUS_SETUP
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Defined but not used.
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.. data:: STATUS_READY
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Connection established.
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.. data:: STATUS_BEGIN
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Connection established. A transaction is in progress.
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.. data:: STATUS_IN_TRANSACTION
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An alias for :data:`STATUS_BEGIN`
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.. data:: STATUS_SYNC
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Defined but not used.
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.. data:: STATUS_ASYNC
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Defined but not used.
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