如何使用psycopg2 / python db api进行数据库事务？ [英] How do I do database transactions with psycopg2/python db api?

问题描述

Im fiddling with psycopg2，虽然有一个.commit（）和.rollback（）没有.begin（）或类似的开始一个事务，或者似乎？
我希望能够做到

Im fiddling with psycopg2 , and while there's a .commit() and .rollback() there's no .begin() or similar to start a transaction , or so it seems ? I'd expect to be able to do

db.begin() # possible even set the isolation level here
curs = db.cursor()
cursor.execute('select etc... for update')
...
cursor.execute('update ... etc.')
db.commit();

那么，事务如何使用psycopg2？
如何设置/更改隔离级别？

So, how do transactions work with psycopg2 ? How would I set/change the isolation level ?

推荐答案

使用 db.set_isolation_level n），假设 db 是您的连接对象。正如Federico写的这里， n 的含义是：

Use db.set_isolation_level(n), assuming db is your connection object. As Federico wrote here, the meaning of n is:

0 -> autocommit
1 -> read committed
2 -> serialized (but not officially supported by pg)
3 -> serialized

如记录此处， psycopg2.extensions 为您提供符号常量：

As documented here, psycopg2.extensions gives you symbolic constants for the purpose:

Setting transaction isolation levels
====================================

psycopg2 connection objects hold informations about the PostgreSQL `transaction
isolation level`_.  The current transaction level can be read from the
`.isolation_level` attribute.  The default isolation level is ``READ
COMMITTED``.  A different isolation level con be set through the
`.set_isolation_level()` method.  The level can be set to one of the following
constants, defined in `psycopg2.extensions`:

`ISOLATION_LEVEL_AUTOCOMMIT`
    No transaction is started when command are issued and no
    `.commit()`/`.rollback()` is required.  Some PostgreSQL command such as
    ``CREATE DATABASE`` can't run into a transaction: to run such command use
    `.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)`.

`ISOLATION_LEVEL_READ_COMMITTED`
    This is the default value.  A new transaction is started at the first
    `.execute()` command on a cursor and at each new `.execute()` after a
    `.commit()` or a `.rollback()`.  The transaction runs in the PostgreSQL
    ``READ COMMITTED`` isolation level.

`ISOLATION_LEVEL_SERIALIZABLE`
    Transactions are run at a ``SERIALIZABLE`` isolation level.


.. _transaction isolation level: 
   http://www.postgresql.org/docs/8.1/static/transaction-iso.html

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