Opened 20 months ago

Last modified 13 months ago

#26149 assigned Bug

Invalid migration generated when using order_with_respect_to and a unique_together constraint

Reported by: Richard Xia Owned by: anabelensc
Component: Migrations Version: 1.9
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no


I ran into a bug when trying to generate and apply a migration for a model that has the order_with_respect_to option set along with a unique_together which involves the implicit _order field created by order_with_respect_to. For example, if you have the following models:

class Bar(models.Model):                                                        

class Foo(models.Model):                                                        
    class Meta:                                                                 
        order_with_respect_to = 'bar'                                           
        unique_together = ('bar', '_order')                                     

    bar = models.ForeignKey(Bar)

when you generate the migrations with make_migrations, it creates a migration with the operations out of order. It attempts to run the AlterUniqueTogether operation before the AlterOrderWithRespectTo, which is problematic because the implicit _order field is created by the latter operation but the former operation tries to create a uniqueness constraint using it. This results in the error: django.core.exceptions.FieldDoesNotExist: Foo has no field named u'_order'

For convenience, I've created a Github repo that sets up the models, so that to reproduce the bug, all you have to do is run makemigrations followed by migrate:

Attachments (2)

migration-bug.patch (1.7 KB) - added by anabelensc 20 months ago.
migration-bug-twotest.patch (6.7 KB) - added by anabelensc 20 months ago.

Download all attachments as: .zip

Change History (10)

comment:1 Changed 20 months ago by Tim Graham

Triage Stage: UnreviewedAccepted

Thanks for the sample project!

Changed 20 months ago by anabelensc

Attachment: migration-bug.patch added

comment:2 Changed 20 months ago by anabelensc

Could you check this patch, please?
I changed "db/migrations/" and now there is no bug.

python makemigrations

Migrations for 'p1':
Create model Bar
Create model Foo
Set order_with_respect_to on foo to bar
Alter unique_together for foo (1 constraint(s))

python migrate

Operations to perform:
Apply all migrations: admin, auth, contenttypes, p1, sessions
Running migrations:
Rendering model states... DONE
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying admin.0002_logentry_remove_auto_add... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying auth.0007_alter_validators_add_error_messages... OK
Applying auth.0008_alter_user_username_max_length... OK
Applying p1.0001_initial... OK
Applying sessions.0001_initial... OK


comment:3 Changed 20 months ago by Tim Graham

Has patch: set
Needs tests: set

A test will be needed, probably in tests/migrations/ If the patch fixes the test and doesn't break any other tests, it might be a good candidate!

comment:4 Changed 20 months ago by anabelensc

thank you, I am working on it .

Changed 20 months ago by anabelensc

Attachment: migration-bug-twotest.patch added

comment:5 Changed 20 months ago by anabelensc

I did a new attachment with the test and patch, could you check, please? Could I do the PR?
Thank you.

comment:6 in reply to:  5 Changed 20 months ago by Dave Peticolas

Replying to anabelensc:

I did a new attachment with the test and patch, could you check, please? Could I do the PR?
Thank you.

Hi, I think there might be a better way to fix this bug. When computing dependencies for index_together and unique_together fields, the autodetector seems to add dependencies on all the related fields on the model, rather than dependencies on the actual fields in the compound index, which might not be related fields at all. They should depend on exactly the fields they index and check_dependencies should return True if the operation is AlterOrderWithRespectTo and the dependency is on the _order fields.

comment:7 Changed 20 months ago by anabelensc

Owner: changed from nobody to anabelensc
Status: newassigned

comment:8 Changed 13 months ago by Tim Graham

Needs tests: unset
Patch needs improvement: set

PR with the attached patch, but there's no discussion about why that solution is preferred despite the previous comment.

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