#28921: On filtering nested many to many fields
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Reporter: Sassan | Owner: nobody
Haradji |
Type: | Status: new
Uncategorized |
Component: Database | Version: 2.0
layer (models, ORM) |
Severity: Normal | Keywords: manytomany query
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Consider that related is a many to many field of Object.
If you filter `Object.objects.filter(related__a=1, related__b=2)` a=1 and
b=2 conditions apply to the same related but if you filter
`Object.objects.filter(related__a=1).exclude(related__b=2)` it returns
Object instances that have a related with a = 1 and they have no related
that has b = 2. It doesn't provide a way to filter Object instances that
have a related with a = 1 which at the same time has b != 2.
Providing `__not...` for each lookup is one way to solve it. But it still
keeps the functionality limited for many to many fields. If user needs all
Object instances which have
1. An related object that has a=1 and b=2
and
2. Another or same related object that has b=3 and c!=4
it can't be done with above.
To achieve this we need a way to categorize many to many field object and
apply conditions to different categories.
One way to do so is to write it like this:
{{{
Object.objects.filter(related__1__a=1, related__1__b=2,
related__2__b=3).exclude(related__2__c=4)
}}}
The role is to consider the optional number after each many to many field
in queries, a category for that many to many field. It is to categorize
conditions.
I doubt if filter method in Django has any idea about state of exclude or
vice versa so I think implementing above in Django is hard. And making
filter and exclude to relate is not intuitive too. Another solution is a
combination of above solutions (`__not...` lookups and lookup categories):
{{{
Object.objects.filter(related__1__a=1, related__1__b=2, related__2__b=3,
related__2__c__neq=4)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/28921>
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