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
570
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
280
Django Through The Years
andrewgodwin
0
180
Writing Maintainable Software At Scale
andrewgodwin
0
420
A Newcomer's Guide To Airflow's Architecture
andrewgodwin
0
330
Async, Python, and the Future
andrewgodwin
2
630
How To Break Django: With Async
andrewgodwin
1
700
Taking Django's ORM Async
andrewgodwin
0
700
The Long Road To Asynchrony
andrewgodwin
0
620
The Scientist & The Engineer
andrewgodwin
1
730
Other Decks in Programming
See All in Programming
Fluent UI Blazor 5 (alpha)の紹介
tomokusaba
0
110
なぜselectはselectではないのか
taiyow
2
270
Go1.24 go vetとtestsアナライザ
kuro_kurorrr
2
350
PHPのガベージコレクションを深掘りしよう
rinchoku
0
230
‘무차별 LGTM~👍’만 외치던 우리가 ‘고봉밥 코드 리뷰’를?
hannah0731
0
500
もう一人で悩まない! 個の知見をチームの知見にする3つの習慣と工夫 / Into team knowledge.
honyanya
3
510
Identifying and Analyzing Fake OSS with Malware - fukuoka.go#21
rhykw
0
520
ベクトル検索システムの気持ち
monochromegane
28
7.9k
PHPでお金を扱う時、終わりのない 謎の1円調査の旅にでなくて済む方法
nakka
3
950
いまさら聞けない生成AI入門: 「生成AIを高速キャッチアップ」
soh9834
11
3.2k
読もう! Android build ドキュメント
andpad
1
190
NestJSのコードからOpenAPIを自動生成する際の最適解を探す
astatsuya
0
160
Featured
See All Featured
10 Git Anti Patterns You Should be Aware of
lemiorhan
PRO
656
60k
Keith and Marios Guide to Fast Websites
keithpitt
411
22k
Statistics for Hackers
jakevdp
797
220k
Understanding Cognitive Biases in Performance Measurement
bluesmoon
27
1.6k
Documentation Writing (for coders)
carmenintech
69
4.7k
Exploring the Power of Turbo Streams & Action Cable | RailsConf2023
kevinliebholz
31
4.7k
How to train your dragon (web standard)
notwaldorf
91
5.9k
4 Signs Your Business is Dying
shpigford
183
22k
How to Create Impact in a Changing Tech Landscape [PerfNow 2023]
tammyeverts
50
2.4k
Rails Girls Zürich Keynote
gr2m
94
13k
Chrome DevTools: State of the Union 2024 - Debugging React & Beyond
addyosmani
4
460
Product Roadmaps are Hard
iamctodd
PRO
52
11k
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 andrewgodwin@eventbrite.com