Models and Migrations and Schemas - oh my!

A talk from DjangoCon US 2012 on South, Django, and schema migrations.

Transcript

1. Models & Migrations & Models & Migrations & Schemas – oh my! Schemas – oh my! Andrew Godwin Andrew Godwin @andrewgodwin @andrewgodwin flickr.com/anders_young flickr.com/anders_young
2. · Django core dev · Django core dev · South · South · Lanyrd · Lanyrd
3. · The Past · The Past django-evolution, south 0.1 django-evolution, south 0.1 · The Present · The Present south 0.7 south 0.7 · The Future · The Future django 1.6? south 2.0? django 1.6? south 2.0?
4. · The Past · The Past django-evolution, south 0.1 django-evolution, south 0.1 · The Present · The Present south 0.7 south 0.7 · The Future · The Future django 1.6? south 2.0? django 1.6? south 2.0?
5. Databases hate schema changes Databases hate schema changes “ “All that optimising gone to waste...” All that optimising gone to waste...” flickr.com/96dpi flickr.com/96dpi
6. · Locks whole tables · Locks whole tables · Hammers disk I/O · Hammers disk I/O · Causes inconsistent results · Causes inconsistent results
7. There's a code/schema split There's a code/schema split Your database is going to ignore git Your database is going to ignore git flickr.com/nataliejohnson flickr.com/nataliejohnson
8. · Extra fields are fine · Extra fields are fine · Missing fields are not · Missing fields are not · Painful/slow to sync · Painful/slow to sync
9. django-evolution django-evolution dmigrations dmigrations
10. South 0.1 South 0.1
13. · South 0.2 · South 0.2 mysql support mysql support
14. · South 0.3 · South 0.3 dependencies dependencies
15. · South 0.4 · South 0.4 altering columns altering columns SQLite SQLite
16. · South 0.5 · South 0.5 ORM freezing ORM freezing Automatic change detection Automatic change detection
17. · South 0.6 · South 0.6 Field introspection Field introspection Dependency solving speed Dependency solving speed
18. · South 0.7 · South 0.7 data/schema split data/schema split missing defaults for NOT NULL missing defaults for NOT NULL multidb multidb custom fields ignored custom fields ignored
19. · The Past · The Past django-evolution, south 0.1 django-evolution, south 0.1 · The Present · The Present south 0.7 south 0.7 · The Future · The Future django 1.6? south 2.0? django 1.6? south 2.0?
20. · Mostly stable · Mostly stable Core API hasn't changed for 2 years Core API hasn't changed for 2 years
21. · No rebase/collapse · No rebase/collapse Needs a big change to migration tracking Needs a big change to migration tracking
22. · Opaque migrations · Opaque migrations Impossible to peek inside migrations Impossible to peek inside migrations
23. · The Past · The Past django-evolution, south 0.1 django-evolution, south 0.1 · The Present · The Present south 0.7 south 0.7 · The Future · The Future django 1.6? south 2.0? django 1.6? south 2.0?
24. django.db.backends.schema django.db.backends.schema
25. · Database abstraction layer · Database abstraction layer Has no idea migrations exist Has no idea migrations exist
26. from django.db import connection from django.db import connection editor = connection.schema_editor() editor = connection.schema_editor() editor.start() editor.start() editor.create_model(Author) editor.create_model(Author) editor.create_model(Book) editor.create_model(Book) editor.commit() editor.commit()
27. from django.db import connection from django.db import connection editor = connection.schema_editor() editor = connection.schema_editor() editor.start() editor.start() editor.alter_field( editor.alter_field( Book, Book, CharField(max_length=100, db_index=True), CharField(max_length=100, db_index=True), TextField(), TextField(), ) ) editor.delete_field(Author, ”age”) editor.delete_field(Author, ”age”) editor.commit() editor.commit()
28. github.com/andrewgodwin/ github.com/andrewgodwin/ django/tree/schema-alteration django/tree/schema-alteration
29. contrib. contrib.migrations migrations
30. · Migration creation/running · Migration creation/running Would replace South Would replace South
31. · Declarative migrations · Declarative migrations Combinable, optimisable Combinable, optimisable
32. · No frozen ORM · No frozen ORM Derived from the migration history Derived from the migration history
33. · Raw SQL support · Raw SQL support For those with beards For those with beards
34. · SQL output support · SQL output support For those with full-flowing beards For those with full-flowing beards
35. from migrations.api import * from migrations.api import * class Migration(BaseMigration): class Migration(BaseMigration): actions = [ actions = [ CreateModel(name = "Author", fields = [ CreateModel(name = "Author", fields = [ ("name", ("name", Field( Field( "django.db.models.fields.CharField", "django.db.models.fields.CharField", [], {"max_length": "100"} [], {"max_length": "100"} )), )), ]) ]) ] ]
36. github.com/andrewgodwin/migrations/ github.com/andrewgodwin/migrations/ Incomplete and broken code! Incomplete and broken code!
37. south 1.0 south 1.0
38. · Python 3 support · Python 3 support To coincide with Django 1.5 To coincide with Django 1.5
39. · Will require Python 2.6 · Will require Python 2.6 As otherwise Python 3 is a PITA As otherwise Python 3 is a PITA
40. All subject to change! All subject to change! This isn't set in stone. This isn't set in stone.
41. · Feedback on schema-alt branch · Feedback on schema-alt branch How to help How to help · Weird and wacky use cases · Weird and wacky use cases · Come talk to me during sprints · Come talk to me during sprints
42. Questions? Questions? Andrew Godwin / @andrewgodwin Andrew Godwin / @andrewgodwin flickr.com/oimax flickr.com/oimax