south talk

Schema Migrations for Django

Friday, September 27, 13

WHAT WE’LL COVER

How to use South

• South and git

• Data migrations

• Model inheritance

• Wacky Stuff


WHY SOUTH?

Generally:

• Migrations allow you to synchronize your database with your code.

• Important for:

• multiple developers• rolling back• migrating data • deploying

Specifically:

• South is the standard

• South is being rolled into Django in 1.7

• South is awesome & fun!


SETTING UPsouth.readthedocs.org


SETTING UP

OR

pip install south

1. Install


SETTING UP2. Installed apps


SETTING UP3. syncdb


SETTING UP(Create an app & models)


SETTING UP

Existing apps:convert_to_south appname

New apps:schemamigration appname --initial

4. Setup each app


HOW IT WORKS

• Migrations folder

• South migrations history table

• Models.py

• Database schema & data

Creates:

Reads from:

Alters:


HOW IT WORKS


NORMAL WORKFLOWupdate modelmanage.py schemamigration appname --automanage.py migrate (appname)

eureka! a better model...manage.py migrate backwards (zero)

update modelmanage.py migrate --list

delete files***redo the schemamigrationmanage.py schemamigration appname --auto

{


NORMAL WORKFLOWupdate modelmanage.py schemamigration appname --automanage.py migrate (appname)

eureka! a better model...manage.py migrate backwards (zero)

update modelmanage.py migrate --list

delete files***redo the schemamigrationmanage.py schemamigration appname --auto

{

DANGER!


AVOIDING GIT TROUBLES



• update Authors model• schemamigration: 0002

• eureka!• migrates back to 0001

• deletes migration 0002• creates new 0002

• writes code• pulls code• migrates to 0002

• writes code• pulls code• ghost migration

Dev #1: Author Dev #2: Blog



Resolving:NEVER

delete a migration that has others have access to




• updates Blog model• schemamigration: 0003

• pushes


• update Blog model• schemamigration: 0002


• pulls





• pushes


• update Blog model• schemamigration: 0002


• pulls

= CONFLICT


AVOIDING GIT TROUBLESBETTER:

git feng shui

models, migrations

other code

other code

previous commit

FEATURE DEVELOPMENT

models, migrations


DATA MIGRATIONSMove date_of_birth from Authors to UserProfile


DATA MIGRATIONSSANDWICH

schemamigration

datamigration

schemamigration


DATA MIGRATIONSBOTTOM SLICE:schemamigration


DATA MIGRATIONSMIDDLE:

datamigration


DATA MIGRATIONSTOP SLICE:

schemamigration

Remove date_of_birth from Author


DATA MIGRATIONSTOP SLICE:

schemamigration

Remove date_of_birth from Author

Remember: Data migration needs all information available.


MODEL INHERITANCE


WACKY STUFF


TESTING


south talk

News & Politics

schemamigration

py migrate

data migrations

model inheritance

update model

py schemamigration

py migrate

schemamigration