#30966: Migration crashes due to foreign key issue, depending on otherwise
irrelevant order on MySQL.
-------------------------------------+-------------------------------------
Reporter: Peter Thomassen | Owner: Hasan
| Ramezani
Type: Bug | Status: assigned
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: migration mySQL | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Hasan Ramezani):
* status: new => assigned
* owner: nobody => Hasan Ramezani
Comment:
I investigate it and think the problem comes from this line:
{{{
related_objects_graph[f.remote_field.model._meta.concrete_model._meta].append(f)
}}}
of
[https://github.com/django/django/blob/30359496a3f3d9af0b02afc334710f7e24c74f5b/django/db/models/options.py#L685
django.db.models.options.Options._populate_directed_relation_graph()]:
I added some log to check `related_objects_graph` in bothe case.
When the migration runs by `./manage.py migrate desecapi 0001` and then
`./manage.py migrate desecapi 0002` (correct case), here is the result:
{{{
defaultdict(<class 'list'>, {<Options for User>:
[<django.db.models.fields.related.ForeignKey: owner>,
<django.db.models.fields.related.ForeignKey: user>], <Options for Domain>:
[<django.db.models.fields.related.ForeignKey: domain>]})
}}}
But, When the migration runs by `./manage.py migrate desecapi 0002` (case
with problem), here is the result:
{{{
defaultdict(<class 'list'>, {<Options for User>:
[<django.db.models.fields.related.ForeignKey: user>], <Options for User>:
[<django.db.models.fields.related.ForeignKey: owner>], <Options for
Domain>: [<django.db.models.fields.related.ForeignKey: domain>]})
}}}
From the result, it is obvious that in the first case we have the
`<Options for User>` key with a value of type list with two items
`[<django.db.models.fields.related.ForeignKey: owner>,
<django.db.models.fields.related.ForeignKey: user>]`.
which generate two alter commands:
{{{
ALTER TABLE `app1_domain` DROP FOREIGN KEY
`app1_domain_owner_id_cc7262a2_fk_app1_user_id`
ALTER TABLE `app1_token` DROP FOREIGN KEY
`app1_token_user_id_5ea51092_fk_app1_user_id`
}}}
But in the second case, we have two keys `<Options for User>` which one
of them has a value of type list with one item
`[<django.db.models.fields.related.ForeignKey: user>]`
and the other has a value of type list with one item
`[<django.db.models.fields.related.ForeignKey: owner>]`.
which generate just one alter command:
{{{
ALTER TABLE `app1_domain` DROP FOREIGN KEY
`app1_domain_owner_id_cc7262a2_fk_app1_user_id`
}}}
Thus, the second foreign key `app1_token_user_id_5ea51092_fk_app1_user_id`
still remains and cause the error.
Any suggestions for a fix?
--
Ticket URL: <https://code.djangoproject.com/ticket/30966#comment:4>
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