On Sep 1, 2011, at 9:38 PM, Arthur Kopatsy wrote: > Thanks Michael. > > I did indeed find out about this solution but that is not exactly the > perfect solution. A migration may do more that just changing the > schema (e.g. UPDATE queries or even python code to correctly transform > the data). These sql statement do not have to go through slony. Only > the DDL changes do. > > Ideally I would like to be able to intercept all the DDL statements > and transform them. Events do not allow me to do that. Is there a way > to mock DDLElement maybe or define my own custom dialect? I am trying > to find the right place to hook that up in the SA code but it is not > obvious.
You can use connection execute events to intercept anything, though in 0.7 these don't have the ability to "circumvent" the statement from actually being emitted to the database, though you can change what the actual statement is, perhaps changing it to a no-op or similar. It's not clear to me how a migration that consists of DDL intermixed with UPDATE statements could function, if all the DDL were not actually executed at that point, but all the UPDATE statements were - don't the UPDATE statements rely upon DDL changes that just occurred prior ? Unless your plan is to generate the SQL to that named script immediately and execute, as the script proceeds. Still, in that case still easy enough to use a different engine, using MockDialect, for all the DDL specific operations. It depends somewhat on what systems you have in place to generate and execute DDL operations. Or the connection events approach could probably handle it as well. http://www.sqlalchemy.org/docs/core/events.html#sqlalchemy.events.ConnectionEvents the docs are a little incomplete here, if you use before_execute() you'd return what was passed: def before_execute(conn, stmt, multiparams, params): return stmt, multiparams, params event.listen(engine, "before_execute", before_execute, retval=True) where "retval=True" means, Connection will use what you return as what it actually executes. Yet another way might be to wrap all your DDL in a new kind of compiled construct that does the "write to a file - then execute that" thing. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
