DjangoCon 2008 Panel: Schema Evolution
summary
Three different migration systems get shown: Demigrations stores raw SQL files with up/down methods, runs manage.py demigrate up/down, and the team reports 14 developers and ~350 migrations in use; South generates Python migrations from Django fields, adds DB independence and a dependency resolver and currently targets Postgres/MySQL (SQLite/Oracle work planned); Django Evolution diffs model signatures, emits hinted or stored mutations and validates them. All warn that DDL may not roll back on MySQL, so backups and staging tests are required.
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chapters (4)
- 0:00Start
- 18:35Pickled summary of Django model • Stores state of Django models at syncdb • Can be diffed against current models • Diffs used to generate hints
- 21:20Best guess at changes required • Can be executed immediately • Can be used as prototype Stored evolution • Can't resolve ambiguous updates (rename) • Can't fill in the blanks (initial data)
- 25:06Core of approach: Hint and Tweak (!magic) • Simple changes without user intervention • Easy entry for customization, raw SQL • Self documenting self auditing • Validation (where possible)
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