Opened 2 years ago

Closed 2 years ago

Last modified 2 years ago

#23288 closed Bug (fixed)

Unable to correctly access data in table during migration

Reported by: Matthew Meyer Owned by: Andrew Godwin
Component: Migrations Version: 1.7-rc-2
Severity: Release blocker Keywords:
Cc: info@…, cmawebsite@… Triage Stage: Ready for checkin
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

I created a profile and then setup some relations to it. When I change the relation from the profile to the User model and try to access the data after the models.py file has been changed but before the migration has been completed the members field returns only a single profile objects instead of the ones that were assigned. Dumping the data shows that users with id 2,3,4,5 are in team with id 1, but when accessing the field from the migration only user id 2 is returned.

Attachments (1)

migration_example.tgz (14.2 KB) - added by Matthew Meyer 2 years ago.
Example application that recreates the problem

Download all attachments as: .zip

Change History (12)

Changed 2 years ago by Matthew Meyer

Attachment: migration_example.tgz added

Example application that recreates the problem

comment:1 Changed 2 years ago by Collin Anderson

Severity: NormalRelease blocker
Triage Stage: UnreviewedAccepted

Yikes! I regret to say I can reproduce this. And it happens even without the Profile-User change to your models.py.

comment:2 Changed 2 years ago by Collin Anderson

I'm out of time, but I put the example on github if someone else wants to give it a try.

compare running the this code by hand in the shell vs in the migration

https://github.com/collinanderson/ticket23288/blob/d3354319e78cf46077fc46e61ff70e201704b264/example/migrations/0002_auto_20140813_1645.py#L9

comment:3 Changed 2 years ago by Markus Holtermann

Cc: info@… added
Needs tests: set

I can confirm the issue too. The repository holds a simplified test case: https://github.com/collinanderson/ticket23288

comment:4 Changed 2 years ago by Collin Anderson

Cc: cmawebsite@… added

The issue happens when querying a many-to-many. The ORM is incorrectly using the ForeignKey relationship.
A deep link to the test case: https://github.com/collinanderson/ticket23288/commit/21a501c963f8a2c50278d438ef1b87cc7cd3031d#diff-186cb93781c2f86fd8d75aac5cd19c2dR6

Last edited 2 years ago by Collin Anderson (previous) (diff)

comment:5 Changed 2 years ago by Andrew Godwin

Owner: changed from nobody to Andrew Godwin
Status: newassigned

Looking at this now.

comment:6 Changed 2 years ago by Andrew Godwin

Well that was nasty. The root cause was that deconstruct() wasn't including related_name, and so both the FK and the M2M ended up with the same related_name - and without model validation running against the migration models (as they're supposedly already validated if deconstruct is accurate) Django didn't catch this and so the filter it passed to the query backend was team__id = X, and Django picked the first thing it knew about with a related_name of "team" - the ForeignKey, not the ManyToMany.

The fix makes sure deconstruct also knows about related_name and a bunch of other similar fields that were missing before (most notably, I have left out limit_choices_to for now as it has no database or model layer effect and returns a set of mostly unserialisable things).

If you have existing migrations from before the fix, you'll either need to regenerate them or manually add related_name into the field definitions yourself (doing this makes the supplied test case pass for me).

comment:7 Changed 2 years ago by Andrew Godwin <andrew@…>

Resolution: fixed
Status: assignedclosed

In 4d2f9c38e835383fe42548353890ed4a302eaa58:

Fixed #23288: deconstruct() ignoring related_name

comment:8 Changed 2 years ago by Collin Anderson

Has patch: set
Needs tests: unset
Resolution: fixed
Status: closednew
Triage Stage: AcceptedReady for checkin

Could use a [1.7.x] backport.

comment:9 Changed 2 years ago by Collin Anderson

Resolution: fixed
Status: newclosed

sorry nevermind. it's right here, the trac hook must have not worked: https://github.com/django/django/commit/b5784048e085e8db5d0e959c12278ef727994e98

comment:10 Changed 2 years ago by Tim Graham <timograham@…>

In 1d79d08d9aef1565cf56d50f0742285efae53631:

Fixed #23294 -- Add related_name to existing migrations.

Thanks to Florian Apolloner for the review; refs #23288.

comment:11 Changed 2 years ago by Tim Graham <timograham@…>

In 41cf159c0ac0a7380874cb6f17464dd741ad1d9b:

[1.7.x] Fixed #23294 -- Add related_name to existing migrations.

Thanks to Florian Apolloner for the review; refs #23288.

Backport of 1d79d08d9a from master

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