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， 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， 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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