Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Digging Into Django's Migrations
Search
Andrew Godwin
September 03, 2014
Programming
3
580
Digging Into Django's Migrations
My keynote from DjangoCon US 2014
Andrew Godwin
September 03, 2014
Tweet
Share
More Decks by Andrew Godwin
See All by Andrew Godwin
Reconciling Everything
andrewgodwin
1
310
Django Through The Years
andrewgodwin
0
200
Writing Maintainable Software At Scale
andrewgodwin
0
440
A Newcomer's Guide To Airflow's Architecture
andrewgodwin
0
350
Async, Python, and the Future
andrewgodwin
2
660
How To Break Django: With Async
andrewgodwin
1
730
Taking Django's ORM Async
andrewgodwin
0
720
The Long Road To Asynchrony
andrewgodwin
0
660
The Scientist & The Engineer
andrewgodwin
1
760
Other Decks in Programming
See All in Programming
Blazing Fast UI Development with Compose Hot Reload (droidcon New York 2025)
zsmb
1
300
AI コーディングエージェントの時代へ:JetBrains が描く開発の未来
masaruhr
1
180
テスト駆動Kaggle
isax1015
0
300
AIと”コードの評価関数”を共有する / Share the "code evaluation function" with AI
euglena1215
1
170
Flutterで備える!Accessibility Nutrition Labels完全ガイド
yuukiw00w
0
160
ソフトウェア品質を数字で捉える技術。事業成長を支えるシステム品質の マネジメント
takuya542
2
13k
Rails Frontend Evolution: It Was a Setup All Along
skryukov
0
160
「テストは愚直&&網羅的に書くほどよい」という誤解 / Test Smarter, Not Harder
munetoshi
0
180
Discover Metal 4
rei315
2
140
ruby.wasmで多人数リアルタイム通信ゲームを作ろう
lnit
3
490
Porting a visionOS App to Android XR
akkeylab
0
480
Deep Dive into ~/.claude/projects
hiragram
14
2.6k
Featured
See All Featured
Product Roadmaps are Hard
iamctodd
PRO
54
11k
Site-Speed That Sticks
csswizardry
10
690
Code Review Best Practice
trishagee
69
19k
Cheating the UX When There Is Nothing More to Optimize - PixelPioneers
stephaniewalter
281
13k
Connecting the Dots Between Site Speed, User Experience & Your Business [WebExpo 2025]
tammyeverts
6
310
4 Signs Your Business is Dying
shpigford
184
22k
RailsConf 2023
tenderlove
30
1.1k
Build your cross-platform service in a week with App Engine
jlugia
231
18k
GitHub's CSS Performance
jonrohan
1031
460k
Rails Girls Zürich Keynote
gr2m
95
14k
CoffeeScript is Beautiful & I Never Want to Write Plain JavaScript Again
sstephenson
161
15k
Why You Should Never Use an ORM
jnunemaker
PRO
58
9.4k
Transcript
's migrations digging into
Andrew Godwin Author of South migrations library Hi, I'm Author
of 1.7 Django migrations Senior Software Engineer at
south migrations for django south.aeracode.org DjangoCon 2008 https://speakerdeck.com/andrewgodwin/south-migrations-for-django
Migrations: They're pretty good.
South 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1.0
Aug 2008 Aug 2008 Sep 2008 Jan 2009 Apr 2009 Jun 2009 Mar 2010 May 2013 Jul 2014
The Early Years 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.8 1.0 Aug 2008 Aug 2008 Sep 2008 Jan 2009 Apr 2009 Jun 2009 Mar 2010 May 2013 Jul 2014
Approaching Stability 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1.0 Aug 2008 Aug 2008 Sep 2008 Jan 2009 Apr 2009 Jun 2009 Mar 2010 May 2013 Jul 2014 Well, in the short term, South 1.0 will be released. “ “ June 2010
The Long Gap & Kickstarter 0.1 0.2 0.3 0.4 0.5
0.6 0.7 0.8 1.0 Aug 2008 Aug 2008 Sep 2008 Jan 2009 Apr 2009 Jun 2009 Mar 2010 May 2013 Jul 2014
Today 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1.0
Aug 2008 Aug 2008 Sep 2008 Jan 2009 Apr 2009 Jun 2009 Mar 2010 May 2013 Jul 2014
For at least a year now, people have been suggesting
to me that South should be in Django core. “ “ June 2010
The Initial Plan Django Schema backend ORM Hooks South 2
Migration handling User interface
The Revised Plan Django Schema backend ORM Hooks South 2
Migration handling User interface Backport for 1.4 - 1.6
The Revised Revised Plan Django Schema backend ORM Hooks Migration
handling User interface
Moving South into Django instead, "Adding migrations to Django"
Logically Separate SchemaEditor Schema Migrations field.deconstruct() ModelOptions.apps Operations Loader /
Graph Executor Autodetector Optimiser State
Operations & State
Operations are a declarative representation of model changes State is
an in-memory representation of entire project state
State State Operation AddModel No Models 1 Model
State State Operation State Operation State Operation State Operation Migration
1 Migration 2
AddModel DeleteModel RenameModel AddField DeleteField AlterModelOptions RenameField AlterModelTable AlterField AlterUniqueTogether
AlterIndexTogether RunSQL RunPython
SchemaEditor
connection.schema_editor() Abstraction over database DDL Takes Django models and fields
with connection.schema_editor() as ed: ed.create_model(Author) ed.add_field( Book, "author", models.ForeignKey(Author), )
Field Deconstruction
Every field has deconstruct() Returns arguments passed to __init__ to
duplicate itself
>>> field = CharField(max_length=255) >>> field.deconstruct() ( None, 'django.db.models.CharField', [],
{'max_length': 255} )
The Graph
Represents migrations and dependencies as directed graph Loop detection, leaf/root
selection
myapp/0001 myapp/0002 otherapp/0001 contenttypes/0001 appthree/0001 myapp/0003 otherapp/0002
The Autodetector
Compares two States and outputs a set of operations to
perform Operations have own dependencies and resolver
Model A Model A w/FK, Model B diff AddModel(B) AddField(A,
"b", FK(B)) dependency sort AddModel(B) AddField(A, "b", FK(B)) BEFORE AFTER
The Optimiser
Takes one set of Operations and outputs another with the
same effect Steps over pairs and checks if they combine and what they pass over
can't reduce reduce possible check conflicts reduced, reset
A New Format More concise Declarative Introspectable
Migration actions Frozen ORM
None
makemigrations field.deconstruct() Loader / Graph Autodetector Optimiser State Writer 1
2 State 3 5 4
migrate SchemaEditor ModelOptions.apps Operations Loader / Graph Executor State 1
2 Recorder 3
In-memory running Creates models from migration sets Autodetector diffs created
from on-disk Used to feed SchemaEditor / ORM
State State Operation State Operation State Operation State Operation Migration
1 Migration 2 Models Models Render Render
But what went wrong?
Swappable Models
Your migration dependencies myapp/0001 myapp/0002 otherapp/0001 auth/0001 contenttypes/0001
myapp/0001 myapp/0002 otherapp/0001 auth/0001 contenttypes/0001 thirdapp/0001 Your migration dependencies on
swappable models
what? Your migration dependencies on swappable models myapp/0001 myapp/0002 otherapp/0001
auth/0001 contenttypes/0001 thirdapp/0001 ???
what? Your migration dependencies on swappable models myapp/0001 myapp/0002 otherapp/0001
auth/0001 contenttypes/0001 thirdapp/0001 ???
Unmigrated Apps
Test persistence
Test persistence on MySQL
Random Meta options order_with_respect_to? Really?
Proxy Models
But we're there! Django 1.7, out now!
Thanks! Andrew Godwin
[email protected]