Alter unique, nullable field to non-unique, nullable fails #100
Description
When a field is nullable and unique, a filtered index is created to enforce uniqueness instead of a unique constraint.
But when the field is made non-unique and still nullable, the generated SQL uses DROP CONSTRAINT instead of DROP INDEX, which doesn't work.
In our case this happened when changing this model:
class MyModel(models.Model):
field1= models.CharField(max_length=254, null=True, unique=True)
field2 = models.ForeignKey('myapp.othermodel', null=False, on_delete=models.deletion.CASCADE)To this model:
class MyModel(models.Model):
field1= models.CharField(max_length=254, null=True)
field2 = models.ForeignKey('myapp.othermodel', null=False, on_delete=models.deletion.CASCADE)
class Meta:
unique_together = ('field2', 'field1')Probably also happens without the unique_together but by just setting unique=False.