This document discusses using South to manage schema migrations for Django projects. South allows databases to stay synchronized with Django models by handling the application and rollback of migrations. It creates migration files to modify the database schema and data migrations to handle moving data between models. The normal workflow with South involves generating migrations with changes to models, running migrations to apply them to the database, and rolling back as needed. It also addresses avoiding issues when multiple developers work with migrations under source control.

1. Schema Migrations for Django
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2. WHAT WE’LL COVER
How to use South
• South and git
• Data migrations
• Model inheritance
•Wacky Stuff
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3. 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!
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4. SETTING UP
south.readthedocs.org
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5. SETTING UP
OR
pip install south
1. Install
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6. SETTING UP
2. Installed apps
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7. SETTING UP
3. syncdb
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8. SETTING UP
(Create an app & models)
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9. SETTING UP
Existing apps:
convert_to_south appname
New apps:
schemamigration appname --initial
4. Setup each app
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10. HOW IT WORKS
• Migrations folder
• South migrations history table
• Models.py
• Database schema & data
Creates:
Reads from:
Alters:
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11. HOW IT WORKS
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12. HOW IT WORKS
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13. HOW IT WORKS
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14. NORMAL WORKFLOW
update model
manage.py schemamigration appname --auto
manage.py migrate (appname)
eureka! a better model...
manage.py migrate backwards (zero)
update model
manage.py migrate --list
delete files***
redo the schemamigration
manage.py schemamigration appname --auto
{
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15. NORMAL WORKFLOW
update model
manage.py schemamigration appname --auto
manage.py migrate (appname)
eureka! a better model...
manage.py migrate backwards (zero)
update model
manage.py migrate --list
delete files***
redo the schemamigration
manage.py schemamigration appname --auto
{
DANGER!
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16. AVOIDING GITTROUBLES
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17. AVOIDING GITTROUBLES
• 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
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18. AVOIDING GITTROUBLES
Resolving:
NEVER
delete a migration that has others have access to
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19. AVOIDING GITTROUBLES
• 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
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20. AVOIDING GITTROUBLES
• 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
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21. AVOIDING GITTROUBLES
BETTER:
git feng shui
models, migrations
other code
other code
previous commit
FEATURE DEVELOPMENT
models, migrations
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22. DATA MIGRATIONS
Move date_of_birth from Authors to UserProfile
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23. DATA MIGRATIONS
SANDWICH
schemamigration
datamigration
schemamigration
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24. DATA MIGRATIONS
BOTTOM SLICE:
schemamigration
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25. DATA MIGRATIONS
MIDDLE:
datamigration
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26. DATA MIGRATIONS
MIDDLE:
datamigration
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27. DATA MIGRATIONS
MIDDLE:
datamigration
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28. DATA MIGRATIONS
TOP SLICE:
schemamigration
Remove date_of_birth from Author
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29. DATA MIGRATIONS
TOP SLICE:
schemamigration
Remove date_of_birth from Author
Remember:
Data migration needs all information available.
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30. MODEL INHERITANCE
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31. MODEL INHERITANCE
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32. MODEL INHERITANCE
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33. MODEL INHERITANCE
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34. WACKY STUFF
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35. TESTING
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