#32838: Migrations create extra index when foreign key is also part of a unique
constraint
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Reporter: levkk | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database | Version: 3.2
layer (models, ORM) | Keywords:
Severity: Normal | postgres,indexes,unique
Triage Stage: | constraint,foreign keys
Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Given a model like so:
{{{
class Person(models.Model):
name = models.TextField()
class Address(models.Model):
person = models.ForeignKey(Person, on_delete=models.PROTECT)
street = models.TextField()
class Meta:
unique_together = ["person", "street"]
}}}
and a Postgres backend, Django will create two btree indexes, one on the
foreign key "person" and another on "person, street" to enforce the unique
constraint. In this case, the "person" index is redundant and wasteful
since the "person, street" index is sufficient. We can check for the
foreign key index being covered by the unique index and not create it if
that's the case.
--
Ticket URL: <https://code.djangoproject.com/ticket/32838>
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