Migrations

Since Django 1.7

New In Django 1.7

Commands

• Makemigrations

  python manage.py makemigrations
  

• Migrate

  python manage.py migrate
  

• Forwards／Backwards

  • Database and Django_migrations Both Change

    python manage.py migrate app_name 0001
    

  • Database Not and Django_migrations Change

    python manage.py migrate app_name 0001 --fake
    

Problems

• ValueError: Cannot serialize:

  • Models

    uid = models.CharField(_(u'uid'), max_length=255, default=shortuuid.uuid, help_text=u'User UUID', db_index=True)
    

  • Description

    ValueError: Cannot serialize: <bound method ShortUUID.uuid of <shortuuid.main.ShortUUID object at 0x1025eab90>>
    There are some values Django cannot serialize into migration files.
    For more, see https://docs.djangoproject.com/en/1.8/topics/migrations/#migration-serializing
    

  • Solution

    • Use ShortUUIDField

    • Installation

      pip install django-shortuuidfield
      

    • ​Usage

      from shortuuidfield import ShortUUIDField
      
      uid = ShortUUIDField(_(u'uid'), max_length=255, help_text=u'User UUID', db_index=True)
      

• No changes detected

  • python manage.py makemigrations - No changes detected
  • python manage.py makemigrations app_name - Changes detected

South

• Conflict

  There is no South database module 'south.db.mysql' for your database. Please either choose a supported database, check for SOUTH_DATABASE_ADAPTER[S] settings, or remove South from INSTALLED_APPS.
  

Before Django 1.7

South

• Install

  pip install south
  

Commands

• Initial

  python manage.py schemamigration app_name --initial
  

• Add-On Field

  python manage.py schemamigration app_name --auto
  

• Exists Projects Convert to Use South

  python manage.py syncdb  # Syncdb has already changed by South, to create table ``south_migrationhistory`` in Database
  python manage.py convert_to_south app_name  # create 0001_initial.py, insert record in table ``south_migrationhistory``
  

• Forwards／Backwards

  • Database and South_migrationhistory Both Change

    python manage.py migrate app_name 0001
    

  • Database Not and South_migrationhistory Change

    python manage.py migrate app_name 0001 --fake
    

Problems

• Multiple Branches

  • Suppose app_name developed in two branches(master and branch2) from 0004

  • At the time of merge, mater is 0007 and branch2 is 0008, and they don't add the same field

  • Solve multiple branches merge

    • Exec command in master branch

      git merge branch2
      

    • Solve conflict

    • south_migrationhistory back to 004

      python manage.py migrate app_name 0004 --fake
      

    • delete migrations after 0004

    • create new migration

      python manage.py schemamigration app_name --auto
      

    • south_migrationhistory back to 0005

      python manage.py migrate app_name 0005 --fake
      

Problems

• Problem after Migrate

  django.db.utils.OperationalError: (1366, "Incorrect string value: '\\xE6\\x95\\xB0\\xE6\\x8D\\xAE...' for column 'name' at row 1")
  

References

[1] ferprez@StackOverflow, There is no South database module 'south.db.postgresql_psycopg2' for your database