La migration de bases de données avec Django et South

Conférence donnée pour la Django Breizh 2012.

1. South les migrations de bases de données avec Django Xavier Ordoquy
2. class Product(models.Model): name = models.CharField(max_length=32) Première itération $ python manage.py syncdb Creating tables ... Creating table step1_project Installing custom SQL ... Installing indexes ... Installed 0 object(s) from 0 fixture(s)
3. class Product(models.Model): name = models.CharField(max_length=32) description = models.CharField(max_length=64) Seconde itération $ python manage.py syncdb Creating tables ... Installing custom SQL ... Installing indexes ... Installed 0 object(s) from 0 fixture(s)
4. Et c’est le drame $ python manage.py shell Python 2.7.2 (default, Jun 20 2012, 16:23:33) >>> from demosouth.step1.models import Product >>> p = Product(name='test', description='demo') >>> p.save() Traceback (most recent call last): [...] DatabaseError: table step1_product has no column named description
5. South • Pour sqlite, mysql, postgres • Migrations forward et backward • Code de migration versionnable ! • utilisé par celery, sentry, django-cms...
6. Fonctionnement • Le code: <app>/migration/00xx_*.py 0001_initial.py 0002_auto__add_field_product_task_status.py • La base: SELECT * FROM south_migrationhistory; app_name | migration | applied projects | 0001_initial | 2012-06-20 09:15:01 projects | 0002_auto__add_..._status | 2012-06-21 06:12:25
7. Voir l’état courant $ python manage.py migrate --list accounts (*) 0001_initial projects (*) 0001_initial ( ) 0002_auto__add_field_product_task_status djcelery (*) 0001_initial (*) 0002_v25_changes
8. Jouer une migration $ python manage.py migrate projects 0002 - Soft matched migration 0002 to 0002_auto__add_[...]_status. Running migrations for projects: - Migrating forwards to 0002_auto__add_ [...]_status. > projects:0002_auto__add_ [...]_status
9. Créer une migration $ python manage.py schemamigration projects --initial + Added model projects.EventLog + Added model projects.Project + Added M2M table for project_manager on projects.Project [...] Created 0001_initial.py. You can now apply this migration with: ./manage.py migrate projects
10. Schéma ou données ? structure ou contenu ?
11. Exemple 1) Ajouter les tables de traduction 2) Remplir les traductions 3) Supprimer les colonnes non traduites
12. Modèle class Product(models.Model): name = models.CharField(max_length=32) description = models.TextField(blank=True, null=True) class Product(models.Model): pass class TranslatedProduct(models.Model): master = models.ForeignKey(Product) language = models.CharField(max_length=8) name = models.CharField(max_length=32) description = models.TextField(blank=True, null=True)
13. Nouvelle structure class Product(models.Model): name = models.CharField(max_length=32) description = models.TextField(blank=True, null=True) class TranslatedProduct(models.Model): master = models.ForeignKey(Product) language = models.CharField(max_length=8) name = models.CharField(max_length=32) description = models.TextField(blank=True, null=True) $ python manage.py schemamigration shop --auto
14. Migrations des données class Migration(DataMigration): def forwards(self, orm): for product in orm.Product.objects.all(): trans = orm.ProductTranslation() trans.name = product.name trans.description = product.description trans.language_code = 'fr' trans.master = product trans.save() $ python manage.py datamigration shop default_translation Created 0003_default_translation.py
15. Nettoyage class Product(models.Model): pass class TranslatedProduct(models.Model): master = models.ForeignKey(Product) language = models.CharField(max_length=8) name = models.CharField(max_length=32) description = models.TextField(blank=True, null=True) $ python manage.py schemamigration shop --auto
16. Installation $ pip install south settings.py : INSTALLED_APPS = ( [...] 'south', )
17. Retour d’expérience • ça marche • indépendant de la base • très simple dans 90% des cas • de la rigueur ! • déploiements simples ! • indispensable pour les applications génériques
18. irc: #django-fr @linovia_net xordoquy@linovia.com Questions ?