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

Friday, September 27, 13

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!

Friday, September 27, 13

SETTING UPsouth.readthedocs.org

Friday, September 27, 13

SETTING UP

OR

pip install south

1. Install

Friday, September 27, 13

SETTING UP2. Installed apps

Friday, September 27, 13

SETTING UP3. syncdb

Friday, September 27, 13

SETTING UP(Create an app & models)

Friday, September 27, 13

SETTING UP

Existing apps:convert_to_south appname

New apps:schemamigration appname --initial

4. Setup each app

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HOW IT WORKS

• Migrations folder

• South migrations history table

• Models.py

• Database schema & data

Creates:

Reads from:

Alters:

Friday, September 27, 13

HOW IT WORKS

Friday, September 27, 13

HOW IT WORKS

Friday, September 27, 13

HOW IT WORKS

Friday, September 27, 13

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

{

Friday, September 27, 13

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!

Friday, September 27, 13

AVOIDING GIT TROUBLES

Friday, September 27, 13

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

Friday, September 27, 13

AVOIDING GIT TROUBLES

Resolving:NEVER

delete a migration that has others have access to

Friday, September 27, 13

AVOIDING GIT TROUBLES

• update Authors model• schemamigration: 0002

• updates Blog model• schemamigration: 0003

• pushes

Dev #1: Author Dev #2: Blog

• update Blog model• schemamigration: 0002

• updates Blog model• schemamigration: 0003

• pulls

Friday, September 27, 13

AVOIDING GIT TROUBLES

• update Authors model• schemamigration: 0002

• updates Blog model• schemamigration: 0003

• pushes

Dev #1: Author Dev #2: Blog

• update Blog model• schemamigration: 0002

• updates Blog model• schemamigration: 0003

• pulls

= CONFLICT

Friday, September 27, 13

AVOIDING GIT TROUBLESBETTER:

git feng shui

models, migrations

other code

other code

previous commit

FEATURE DEVELOPMENT

models, migrations

Friday, September 27, 13

DATA MIGRATIONSMove date_of_birth from Authors to UserProfile

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DATA MIGRATIONSSANDWICH

schemamigration

datamigration

schemamigration

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DATA MIGRATIONSBOTTOM SLICE:schemamigration

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DATA MIGRATIONSMIDDLE:

datamigration

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DATA MIGRATIONSMIDDLE:

datamigration

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DATA MIGRATIONSMIDDLE:

datamigration

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DATA MIGRATIONSTOP SLICE:

schemamigration

Remove date_of_birth from Author

Friday, September 27, 13

DATA MIGRATIONSTOP SLICE:

schemamigration

Remove date_of_birth from Author

Remember: Data migration needs all information available.

Friday, September 27, 13

MODEL INHERITANCE

Friday, September 27, 13

MODEL INHERITANCE

Friday, September 27, 13

MODEL INHERITANCE

Friday, September 27, 13

MODEL INHERITANCE

Friday, September 27, 13

WACKY STUFF

Friday, September 27, 13

TESTING

Friday, September 27, 13