Models and Migrations and Schemas - oh my!

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

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

· 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?

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

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

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

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

django-evolution django-evolution dmigrations dmigrations

South 0.1 South 0.1

· South 0.2 · South 0.2 mysql support mysql support

· South 0.3 · South 0.3 dependencies dependencies

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

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

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

· 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

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

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

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

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

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

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()

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()

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

contrib. contrib.migrations migrations

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

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

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

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

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

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

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

south 1.0 south 1.0

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

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

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

· 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

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

Models and Migrations and Schemas - oh my!

Models and Migrations and Schemas - oh my!

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