Comments on: SQLAlchemy-Migrate upgrade scripts in a transaction

By: dazza

dazza — Mon, 28 Jul 2008 12:46:30 +0000

@sacha: you are correct, by using env to launch python it will pick it up from the environment that the script is running in. It is just to stop a hard coded paths in the script. It’s not actually needed for this particular script since it is being invoked by an already running python interpreter but it’s part of my ‘new python template’ in TextMate.

The encoding is to follow PEP 263 http://www.python.org/dev/peps/pep-0263/ It just makes sure all unicode literals embedded in the code are in UTF8. Everything I do is in UTF8 so it stops non UTF8 string slipping in to the code base and causing interesting and sometimes difficult to track down bugs.

By: Sacha Varma

Sacha Varma — Mon, 28 Jul 2008 11:32:06 +0000

Python nub questions:

#!/usr/bin/env python
# encoding: utf-8

/usr/bin/env? Why not just /usr/bin/python? Is this just a way of not having to explicitly specify the location of python, and have it pick it up from your $PATH?

The encoding line presumably relates to the source code that follows?

By: dazza

dazza — Mon, 28 Jul 2008 10:42:49 +0000

@Sacha Varma: there is a new command added in the latest version which creates a script from a diff between the database and your ‘model’ make_update_script_for_model.

See the change list here http://code.google.com/p/sqlalchemy-migrate/wiki/ChangesSince0_4_4. I haven’t used this myself but I think it does what you want.

By: Sacha Varma

Sacha Varma — Mon, 28 Jul 2008 10:21:52 +0000

If you have an old model.py (A) and a new model.py (B), do you have to write the code to upgrade from A to B, or is there a tool that “diffs” the two and spits out the code to do the upgrade/downgrade?

By: dazza

dazza — Mon, 28 Jul 2008 10:13:26 +0000

@Sacha Varma: your correct, there is no overall upgrade wrapper. Indeed it would be nice if all this was covered by the sqlalchemy-migrate. There has been some chatter on the sqlalchemy-migrate group about this. This is just a small step toward a bigger goal.

To manage code and database changes I version control the migrate repository in svn. So I can be sure that the code I update checkout syncs with upgrade scripts I am about to run.

By: Sacha Varma

Sacha Varma — Mon, 28 Jul 2008 09:55:06 +0000

A couple of questions:

1. I can see that this would work when upgrading the database one revision at a time, but if sqlalchemy-migrate applies multiple updates in sequence, you’d probably want a transaction around the whole sequence? (i.e. I reckon sqlalchemy-migrate should do the rollback management)

2. How do you manage updates that involve not just database changes, but also template & code changes? Is there a ‘turbogears-migrate’ that incorporates sqlalchemy-migrate?