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
330
Django Through The Years
andrewgodwin
0
220
Writing Maintainable Software At Scale
andrewgodwin
0
460
A Newcomer's Guide To Airflow's Architecture
andrewgodwin
0
370
Async, Python, and the Future
andrewgodwin
2
680
How To Break Django: With Async
andrewgodwin
1
740
Taking Django's ORM Async
andrewgodwin
0
740
The Long Road To Asynchrony
andrewgodwin
0
680
The Scientist & The Engineer
andrewgodwin
1
790
Other Decks in Programming
See All in Programming
20251016_Rails News ~Rails 8.1の足音を聴く~
morimorihoge
2
570
ソフトウェア設計の実践的な考え方
masuda220
PRO
4
620
CSC305 Lecture 06
javiergs
PRO
0
250
Server Side Kotlin Meetup vol.16: 内部動作を理解して ハイパフォーマンスなサーバサイド Kotlin アプリケーションを書こう
ternbusty
3
220
EMこそClaude Codeでコード調査しよう
shibayu36
0
240
実践Claude Code:20の失敗から学ぶAIペアプログラミング
takedatakashi
15
6.1k
Building, Deploying, and Monitoring Ruby Web Applications with Falcon (Kaigi on Rails 2025)
ioquatix
4
2.3k
One Enishi After Another
snoozer05
PRO
0
130
Android16 Migration Stories ~Building a Pattern for Android OS upgrades~
reoandroider
0
130
オープンソースソフトウェアへの解像度🔬
utam0k
16
3.1k
SwiftDataを使って10万件のデータを読み書きする
akidon0000
0
230
Go言語はstack overflowの夢を見るか?
logica0419
0
490
Featured
See All Featured
Building a Scalable Design System with Sketch
lauravandoore
463
33k
Leading Effective Engineering Teams in the AI Era
addyosmani
7
510
Balancing Empowerment & Direction
lara
5
690
The Psychology of Web Performance [Beyond Tellerrand 2023]
tammyeverts
49
3.1k
A designer walks into a library…
pauljervisheath
209
24k
CSS Pre-Processors: Stylus, Less & Sass
bermonpainter
359
30k
[RailsConf 2023 Opening Keynote] The Magic of Rails
eileencodes
31
9.7k
The Power of CSS Pseudo Elements
geoffreycrofte
79
6k
RailsConf & Balkan Ruby 2019: The Past, Present, and Future of Rails at GitHub
eileencodes
140
34k
Responsive Adventures: Dirty Tricks From The Dark Corners of Front-End
smashingmag
253
22k
VelocityConf: Rendering Performance Case Studies
addyosmani
332
24k
4 Signs Your Business is Dying
shpigford
185
22k
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]