Opened 10 years ago

Last modified 10 years ago

#24447 closed Bug

Migrations do not add a FK constraint for an existing column — at Version 4

Reported by: Jean-Louis Fuchs Owned by: nobody
Component: Migrations Version: 1.7
Severity: Normal Keywords:
Cc: Markus Holtermann Triage Stage: Ready for checkin
Has patch: yes Needs documentation: yes
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no

Description (last modified by Jean-Louis Fuchs)

Pull request: ​https://github.com/django/django/pull/4235

Consider following model:

class ForeignKeyTest(models.Model):
    id = models.AutoField(primary_key=True)
    customer = models.IntegerField()

class Customer(models.Model):
    id = models.AutoField(primary_key=True)

Then it gets migrated to this:

class ForeignKeyTest(models.Model):
    id = models.AutoField(primary_key=True)
    customer = models.ForeignKey('Customer')

class Customer(models.Model):
    id = models.AutoField(primary_key=True)

The second migration won't create the foreign key. This does not fail with sqlite! Because these migrations are handled differently. It will fail with MySQL and probably Postgres too.

The code didn't detect this case: if old_field.rel doesn't exist alter_field() must always create the foreign key and ONLY if .rel exists it must check .db_constraint, too. Since no .rel also means there was no foreign key before.

Change History (4)

comment:1 by Tim Graham, 10 years ago

Patch needs improvement: set
Triage Stage: Unreviewed → Accepted

comment:2 by Markus Holtermann, 10 years ago

Version: master → 1.7

comment:3 by Markus Holtermann, 10 years ago

Cc: Markus Holtermann added
Needs documentation: set

comment:4 by Jean-Louis Fuchs, 10 years ago

Description: modified (diff)
Summary: Migrations do not execute create_fk_sql() when adding a foreign key to a field → Migrations do not add a FK constraint for an existing column

Removed redundant information and chose clearer title.

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