On Sep 30, 2012, at 9:48 PM, Roy Shan wrote:
> Hi, Michael:
>
> I am trying to use server_onupdate in schema definition, but server_onupdate
> doesn't seem to work.
>
> Here's an example:
>
> from sqlalchemy import *
> engine = create_engine('mysql://root:@localhost:3306/test?charset=utf8', echo
> =True)
> m = MetaData(bind=engine)
> t = Table('t', m,
> Column('a', Integer),
> Column('b', TIMESTAMP(), server_onupdate=text('current_stamp'))
> )
> m.drop_all()
> m.create_all()
>
> the output of this script is:
>
> CREATE TABLE t (
> a INTEGER,
> b TIMESTAMP NULL
> )
>
> The server_onupdate has no effect.
While it seems like it should, that's currently not what server_onupdate does.
Most databases do not support an inline form of "ON UPDATE" within column
definitions; MySQL is an exception to this but we do not support MySQL's syntax
directly right now. server_onupdate's purpose is to place a marker on the
column, so that the ORM knows that some separately defined trigger or rule has
been established that will cause the column to receive a new value when an
UPDATE statement executes.
To render MySQL's ON UPDATE you'd need to emit a separate ALTER instruction for
now. 0.8 will offer a compile hook, but this is still not a first class
"mysql_onupdate" feature as of yet.
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