[Django] #19018: m2m relationships with a through field don't respect types.

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Sep 24, 2012, 2:25:42 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.
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Reporter: justinlilly | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer (models, ORM) | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I ran into an issue today in which an empty list was returned from a
Queryset when it should have been a blatant failure.

Given the models in
https://github.com/django/django/blob/master/tests/modeltests/m2m_through/models.py

The following returns an empty queryset:

{{{#!python
Group.objects.filter(members__in=[Friendship(pk=9)])
}}}

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Ticket URL: <https://code.djangoproject.com/ticket/19018>
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Django

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Sep 24, 2012, 2:26:07 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

Easy pickings: 0 | UI/UX: 0

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Changes (by justinlilly):

* needs_better_patch: => 0
* type: Uncategorized => Bug
* needs_tests: => 0
* needs_docs: => 0

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Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:1>

Django

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Sep 24, 2012, 2:27:05 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

-------------------------------------+-------------------------------------
Reporter: justinlilly | Owner: nobody

Type: Bug | Status: new
Component: Database layer | Version: 1.4
(models, ORM) | Resolution:

* stage: Unreviewed => Accepted

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Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:2>

Django

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Sep 24, 2012, 2:38:32 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

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Reporter: justinlilly | Owner: nobody

Comment (by carljm):

I don't believe this bug is specific to m2ms or through models at all. In
general, currently you can pass any iterable of instances of any model to
any `__in` query and the ORM will happily use the PKs of the models you
give it, without checking whether they are an instance of the right model
class (or a subclass, or raw PK values which is also supported).

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Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:3>

Django

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Sep 24, 2012, 2:39:13 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

-------------------------------------+-------------------------------------
Reporter: justinlilly | Owner: nobody

Comment (by carljm):

(Also not specific to `__in` queries, same is true of a simple `__exact`
match on an FK field).

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Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:4>

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Sep 24, 2012, 2:39:39 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

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Reporter: justinlilly | Owner: nobody

Comment (by Alex):

Everything you just said is correct, it's not just your belief :)

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Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:5>

Django

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Sep 24, 2012, 3:01:20 PM9/24/12

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#19018: m2m relationships with a through field don't respect types.

-------------------------------------+-------------------------------------
Reporter: justinlilly | Owner: nobody

Comment (by ptone):

So looking at this mostly for my own edification.

A higher level place this could be checked would be
`db.models.where.Constraint.process`

otherwise: `db.models.fields.related.RelatedField.get_db_prep_lookup` and
`db.models.fields.related.RelatedField._pk_trace`

seem like the best places to tackle this.

However unless a patch is pretty quick, it seems worth improving the docs,
at least in the interim, to clarify that lookup values for model instances
will always be converted to a simple pk value for database lookups.

--
Ticket URL: <https://code.djangoproject.com/ticket/19018#comment:6>

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Mar 13, 2015, 8:34:34 AM3/13/15

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#19018: m2m relationships with a through field don't respect types.

-------------------------------------+-------------------------------------
Reporter: justinlilly | Owner: nobody
Type: Bug | Status: closed

Component: Database layer | Version: 1.4
(models, ORM) |

Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Accepted

Has patch: 0 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0

Easy pickings: 0 | UI/UX: 0

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Changes (by knbk):