Django filter not working when using F() with ManyToMany

Question

I have the following query:

MyModel.objects.filter(foreing_key__value=F('value'))

And It works perfectly. But now I have some complex rules where I need to evaluate the ForeignKey value depending on some conditions. Just to simplify, if I refactor the query to:

MyModel.objects.annotate(
  valid_value=F('foreing_key__value')
).filter(
  valid_value=F('value')
)

It doesn't work when the foreing_key__value is NULL. Why is this happening? I think it's related to LEFT JOIN, which is not applied when using the F() operator, but I'm unsure how to fix this issue.

Thanks in advance

Is valid_value itself NULL? It might be more useful to give some (sample) models and explain what you aim to achieve. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Nov 12, 2024 at 20:24
@willeM_VanOnsem Thanks for your time, I've fixed it checking by null values if F() operator is applied — Genarito
– Genarito, Commented Nov 12, 2024 at 21:00

Genarito · Accepted Answer · 2024-11-12 20:59:39Z

1

For some reason, the filters with Q() work when using the field name. But when F() is applied, it evaluates to None, and Q() with equal conditions doesn't work as expected.

I have to fix it using the following code:

MyModel.objects.annotate(
  valid_value=F('foreing_key__value')
).filter(
  Q(valid_value__isnull=False) & Q(valid_value=F('value'))
)

answered Nov 12, 2024 at 20:59

Genarito

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white.seolpyo.com · Accepted Answer · 2024-11-16 00:40:20Z

0

Fields in foreign keys or many-to-many models can be filtered without annotating them.

# MyModel.objects.filter(m2m_or_foreignkey__field=123)
MyModel.objects.filter(foreign_key__value=123)

answered Nov 16, 2024 at 0:40

white.seolpyo.com

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1 Comment

Genarito Over a year ago

Yep, but I have a complex Case/When so I need to make annotations. The example was just a simplified version of the problem

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