Models and Migrations and Schemas - oh my!

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Models & Migrations & Models & Migrations & Schemas – oh my! Schemas – oh my! Andrew Godwin Andrew Godwin @andrewgodwin @andrewgodwin flickr.com/anders_young flickr.com/anders_young

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· Django core dev · Django core dev · South · South · Lanyrd · Lanyrd

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· 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?

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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

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· Locks whole tables · Locks whole tables · Hammers disk I/O · Hammers disk I/O · Causes inconsistent results · Causes inconsistent results

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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

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· Extra fields are fine · Extra fields are fine · Missing fields are not · Missing fields are not · Painful/slow to sync · Painful/slow to sync

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django-evolution django-evolution dmigrations dmigrations

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South 0.1 South 0.1

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· South 0.2 · South 0.2 mysql support mysql support

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· South 0.3 · South 0.3 dependencies dependencies

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· South 0.4 · South 0.4 altering columns altering columns SQLite SQLite

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· South 0.5 · South 0.5 ORM freezing ORM freezing Automatic change detection Automatic change detection

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· South 0.6 · South 0.6 Field introspection Field introspection Dependency solving speed Dependency solving speed

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· 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

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· Mostly stable · Mostly stable Core API hasn't changed for 2 years Core API hasn't changed for 2 years

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· No rebase/collapse · No rebase/collapse Needs a big change to migration tracking Needs a big change to migration tracking

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· Opaque migrations · Opaque migrations Impossible to peek inside migrations Impossible to peek inside migrations

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django.db.backends.schema django.db.backends.schema

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· Database abstraction layer · Database abstraction layer Has no idea migrations exist Has no idea migrations exist

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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()

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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()

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github.com/andrewgodwin/ github.com/andrewgodwin/ django/tree/schema-alteration django/tree/schema-alteration

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contrib. contrib.migrations migrations

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· Migration creation/running · Migration creation/running Would replace South Would replace South

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· Declarative migrations · Declarative migrations Combinable, optimisable Combinable, optimisable

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· No frozen ORM · No frozen ORM Derived from the migration history Derived from the migration history

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· Raw SQL support · Raw SQL support For those with beards For those with beards

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· SQL output support · SQL output support For those with full-flowing beards For those with full-flowing beards

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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"} )), )), ]) ]) ] ]

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github.com/andrewgodwin/migrations/ github.com/andrewgodwin/migrations/ Incomplete and broken code! Incomplete and broken code!

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south 1.0 south 1.0

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· Python 3 support · Python 3 support To coincide with Django 1.5 To coincide with Django 1.5

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· Will require Python 2.6 · Will require Python 2.6 As otherwise Python 3 is a PITA As otherwise Python 3 is a PITA

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All subject to change! All subject to change! This isn't set in stone. This isn't set in stone.

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· 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

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Questions? Questions? Andrew Godwin / @andrewgodwin Andrew Godwin / @andrewgodwin flickr.com/oimax flickr.com/oimax