Migrating with South

A talk I gave at DJUGL #2

Transcript

1. south
   Andrew�Godwin
   Migrating�with
   andrew@aeracode.org
   

   View Slide

2. One�of�many
   south
   Migrating�with
   django-evolution
   migratory
   dmigrations
   deseb
   

   View Slide

3. Two�parts
   south
   Migrating�with
   migration�engine
   database�abstractor
   MySQL
   PostgreSQL
   SQLite
   SQL�Server
   tracking
   dependencies
   conflicts
   

   View Slide

4. What�are�migrations?
   south
   Migrating�with
   /�mutations�/�diffs�/�etc
   

   View Slide

5. Problem:�database�schema�isn't
   meaningfully�versioned
   south
   Migrating�with
   -�It's�usually�in�a�VCS�(models.py),�but�the
   ��database�exists��outside�of�version�control.
   -�Migration�libraries�essentially�add�version�control
   ��to�database�schemas.
   

   View Slide

6. South�keeps�its�distance�from�models.py.
   south
   Migrating�with
   You're�never�sure�if�it's�from�the�past,�present�or�future.
   (see:�cheesy�time-travel�films)
   

   View Slide

7. You�can�use�it,�though.
   south
   Migrating�with
   While�migrations�are�independent�from�it,�they�can
   be�made�from�models.py�automatically.
   

   View Slide

8. A�migration! south
   Migrating�with
   from south.db import db
   from core.models import *
   cl ass Migration:
   def forwards(self):
   db.add_column("core_nation", "slug",
   models.SlugField(unique=True, default="test")
   )
   def backwards(self):
   db.add_column("core_nation", "slug")
   

   View Slide

9. How�is�migration�formed? south
   Migrating�with
   ./manage.py startmigration core test_migration
   The�South�command App�name Migration�name
   ./manage.py startmigration core \
   test_migration
   Blank�migration:
   Add�everything�(initial;�replaces�the�syncdb):
   --initial
   ./manage.py startmigration core \
   test_migration
   Add�a�new�field:
   --add-field Picture.slug
   These�all�make�a�file�like�c ore/migrations/0002_test_migration.py.
   

   View Slide

10. Migrations�are�per-app.
    south
    Migrating�with
    If�an�app�doesn't�need�migrations,�it�uses�syncdb�as�normal.
    If�apps�depend�on�others,�there's�a�dependency�resolver.
    

    View Slide

11. Installation
    south
    Migrating�with
    Put�South�somewhere�on�the�Python�path
    svn co http://.../trun k/south/ easy_install South
    or
    Add�it�to�INSTALLED_APPS
    INSTALLED_APPS = [ ... , "south" ]
    Run�syncdb�(South�uses�a�table�to�track�applied�migrations)
    ./manage.py syncdb
    That's�it.�Start�migrating.
    (We�have�docs�on�things�like�converting�existing�apps)
    

    View Slide

12. Database�Abstraction
    south
    Migrating�with
    Sigh.
    

    View Slide

13. south
    Migrating�with
    epic�fail fail win
    M
    ySQL
    Postgres
    SQLite
    SQL�Server
    Highly�scientific�graph
    No�DDL�Transactions
    No�Column�Alters Awesome.
    Ugh.
    

    View Slide

14. south
    Migrating�with
    We�have�good�support�for�PostgreSQL�and�MySQL
    But�MySQL�users�can't�wrap�migrations�in�transactions.
    We�have�alright�support�for�SQLite
    Haven't�got�the�alter_column�workarounds�in�yet.
    We�have�basic�support�for�SQL�Server
    It�wasn't�me,�honest.
    

    View Slide

15. south
    Migrating�with
    # M
    ock M
    odel s
    User = db.mock_model(model_name='User', db_table='auth_user', db_tablespace='',
    pk_field_name='id', pk_field_type=models.AutoField)
    # M
    odel ' User Pr of i l e'
    db.create_table('core_userprofile', (
    ('id', models.AutoField(verbose_name='ID', primary_key=True, auto_created=True)),
    ('user', models.OneToOneField(User, related_name="profile")),
    ))
    API�Example
    

    View Slide

16. south
    Migrating�with
    The�Future
    ORM�in�migrations
    More�databases
    Robust�models.py�parsing
    

    View Slide

17. south
    Migrating�with
    Fin.
    http://south.aeracode.org
    Ideas,�tickets�and�patches�always�welcome
    Andrew�Godwin andrew@aeracode.org
    

    View Slide