Django Migrations: A Retrospective

A talk I gave at DjangoCon AU 2014.

Transcript

1. Andrew Godwin
   @andrewgodwin
   migrations:
   a retrospective
   

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2. Andrew Godwin
   Author of South migrations library
   Hi, I'm
   Author of 1.7 Django migrations
   I like my tea iced, and my schemas explicit
   

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3. Django/Python backend
   I work for
   Discovery? Mobile? Storage? UI?
   On-site? ...auditing? We have it all.
   We're hiring!
   

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4. Migrations
   They're pretty good.
   

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5. South
   ...it was good for its time
   

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6. The Initial Plan
   Django
   Schema backend
   ORM Hooks
   South 2
   Migration handling
   User interface
   

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7. The Revised Plan
   Django
   Schema backend
   ORM Hooks
   South 2
   Migration handling
   User interface
   Backport for 1.4 - 1.6
   

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8. The Revised Revised Plan
   Django
   Schema backend
   ORM Hooks
   Migration handling
   User interface
   

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9. Logically Separate
   SchemaEditor
   Schema Migrations
   field.deconstruct()
   ModelOptions.apps
   Operations
   Loader / Graph
   Executor
   Autodetector
   Optimiser
   State
   

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10. makemigrations
    field.deconstruct()
    Loader / Graph
    Autodetector Optimiser
    State
    Writer
    1
    2
    State
    3
    5
    4
    

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11. migrate
    SchemaEditor
    ModelOptions.apps
    Operations
    Loader / Graph Executor
    State
    1 2
    Recorder
    3
    

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12. Moving South into Django
    instead, "Adding migrations to Django"
    

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13. A New Format
    More concise
    Declarative
    Introspectable
    

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14. Migration actions
    Frozen ORM
    

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16. In-memory running
    Creates models from migration sets
    Autodetector diffs created from on-disk
    Used to feed SchemaEditor / ORM
    

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17. But what went wrong?
    

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18. Swappable Models
    

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19. Your migration dependencies
    myapp/0001
    myapp/0002
    otherapp/0001
    auth/0001
    contenttypes/0001
    

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20. myapp/0001
    myapp/0002
    otherapp/0001
    auth/0001
    contenttypes/0001
    thirdapp/0001
    Your migration dependencies
    on swappable models
    

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21. what?
    Your migration dependencies
    on swappable models
    myapp/0001
    myapp/0002
    otherapp/0001
    auth/0001
    contenttypes/0001
    thirdapp/0001
    ???
    

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22. what?
    Your migration dependencies
    on swappable models
    myapp/0001
    myapp/0002
    otherapp/0001
    auth/0001
    contenttypes/0001
    thirdapp/0001
    ???
    

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23. Unmigrated Apps
    

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24. Test persistence
    

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25. Test persistence
    on MySQL
    

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26. Random Meta options
    order_with_respect_to? Really?
    

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27. Proxy Models
    

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28. But we're close!
    Django 1.7, coming to a server near you soon.
    

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29. Thanks!
    Andrew Godwin
    andrewgodwin@eventbrite.com
    

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