#31399: SchemaEditor._alter_field() looks for foreign key constraints even if
the
database doesn't support them
--------------------------------------+------------------------
Reporter: Tim Graham | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
--------------------------------------+------------------------
`BaseDatabaseSchemaEditor._alter_field()`
[https://github.com/django/django/blob/895f28f9cbed817c00ab68770433170d83132d90/django/db/backends/base/schema.py#L572-L582
does a lookup for foreign key constraints] even if the database doesn't
support them, resulting in test failures like this:
{{{
======================================================================
ERROR: test_alter_field_fk_keeps_index (schema.tests.SchemaTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/tim/code/django/tests/schema/tests.py", line 990, in
test_alter_field_fk_keeps_index
editor.alter_field(Book, old_field, new_field, strict=True)
File "/home/tim/code/django/django/db/backends/base/schema.py", line
535, in alter_field
old_db_params, new_db_params, strict)
File "/home/tim/code/django/django/db/backends/base/schema.py", line
548, in _alter_field
old_field.column,
ValueError: Found wrong number (0) of foreign key constraints for
schema_book.author_id
}}}
This is a problem only when the argument `strict=True` is used (which I
believe is only in tests).
To fix this, `self.connection.features.supports_foreign_keys` should be
consulted.
--
Ticket URL: <https://code.djangoproject.com/ticket/31399>
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