#34304 closed Bug (fixed)
Adding and removing a conditional UniqueConstraint to ForeignKey multiple times crashes on MySQL
Reported by: | Sage Abdullah | Owned by: | Sage Abdullah |
---|---|---|---|
Component: | Database layer (models, ORM) | Version: | 4.2 |
Severity: | Release blocker | Keywords: | GeyseR |
Cc: | mysql | Triage Stage: | Accepted |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description (last modified by )
Adding and removing a UniqueConstraint
to ForeignKey
with a condition
more than once on MySQL will crash the schema editor an OperationalError
, e.g. django.db.utils.OperationalError: (1061, "Duplicate key name 'schema_book_author_id_c80c8297'")
Test in tests.schema.tests
:
def test_unique_with_fk_and_condition_multiple_times(self): """ Tests adding and removing a unique constraint to ForeignKey with a condition multiple times. """ with connection.schema_editor() as editor: editor.create_model(Author) editor.create_model(Book) constraint = UniqueConstraint( "author", condition=Q(title__in=["tHGttG", "tRatEotU"]), name="book_author_condition_uniq", ) for i in range(2): # Add constraint. with connection.schema_editor() as editor: editor.add_constraint(Book, constraint) sql = constraint.create_sql(Book, editor) book_table = Book._meta.db_table constraints = self.get_constraints(book_table) if connection.features.supports_partial_indexes: self.assertIn(constraint.name, constraints) self.assertIs(constraints[constraint.name]["unique"], True) self.assertIn("WHERE %s IN" % editor.quote_name("title"), str(sql)) else: self.assertNotIn(constraint.name, constraints) self.assertIsNone(sql) # Remove constraint. with connection.schema_editor() as editor: editor.remove_constraint(Book, constraint) self.assertNotIn(constraint.name, self.get_constraints(book_table))
This is a regression in b731e8841558ee4caaba766c83f34ea9c7004f8b.
Use case:
Wagtail supports multiple database backends. We have a migration that adds a unique constraint to a foreign key with a condition. In addition, we also have migrations that alter the field referenced in the condition. Before making an alter field operation, we need to remove the unique constraint to avoid violating the constraint, then re-add the constraint after the field has been altered. We have more than one migrations that do these operations, thus triggering the error. This issue only happens on MySQL, specifically after the above commit was merged into Django. Even though conditional indexes aren't supported on MySQL, I believe it should just be ignored (as with previous releases) instead of crashing the schema editor.
Relevant migrations in Wagtail:
- 0050_workflow_rejected_to_needs_changes: First instance of
RemoveConstraint
andAddConstraint
- 0060_fix_workflow_unique_constraint: another instance, this fails to run. (Though, I know this migration doesn't really do anything.)
Change History (6)
comment:1 by , 23 months ago
Description: | modified (diff) |
---|
comment:2 by , 23 months ago
Description: | modified (diff) |
---|
comment:3 by , 23 months ago
Has patch: | set |
---|
comment:4 by , 23 months ago
Cc: | added |
---|---|
Component: | Migrations → Database layer (models, ORM) |
Keywords: | GeyseR added |
Severity: | Normal → Release blocker |
Triage Stage: | Unreviewed → Accepted |
Thanks for the report.
PR.