Creating Partial Indexes with Django 1.7

Question

The documentation for Django 1.7 mentions RunSQL classes can be used to create partial indexes on your tables. I have a table where I want the combination of

Answer 1

You could just provide an unique_together like so:

class Post(models.Model):
    title = models.CharField(max_length=200)
    blog = models.ForeignKey(Blog)
    category = models.ForeignKey(Category, null=True, blank=True)

class Meta:
    unique_together = ("title", "blog", "category")

NULLs for category will work how you want in that if not set then title/blog has to be unique.

https://docs.djangoproject.com/en/1.8/ref/models/options/#unique-together

Answer 2

Django 2.2 and later

As of version 2.2 Django supports declarative partial unique indexes on databases that support them (PostgreSQL and SQLite). So you could do something like:

from django.db.models import Model, Q, UniqueConstraint

class Post(Model):
    ...
    class Meta:
        constraints = [
            UniqueConstraint(
                fields=["title", "blog", "category"],
                name="idx1",
                condition=Q(category__isnull=False)),
            UniqueConstraint(
                fields=["title", "blog"], 
                name="idx2",                    
                condition=Q(category__isnull=True)),
        ]

Django 2.1 and earlier

In older versions you need to do this with migrations. First create a new, empty migration file:

python manage.py makemigrations --empty yourappname

Then, for each index add an appropriate RunSQL line:

operations = [
    migrations.RunSQL("CREATE UNIQUE INDEX..."),
    migrations.RunSQL("CREATE UNIQUE INDEX..."),
]

Finally, run migrate.