Django 3.0 Python 3.* - Nested Queries and Filters

Question

Scenario: Form that give values to filter some records. I have 4 models A, B, C and D.

A Have OneToOne relationship with B

B Have ManyToOne relationship with C

C Have ManyToOne relationship with D

Form value given is a field in model D, and the record that I'll retrieve is in model A

I've Tried:

records= A.objects.filter(
            a_field = "form_given_value_1",
            B__b_field = C.objects.filter( 
                c_field = D.objects.filter(
                    d_field=form_given_value_2
                )
            )
        )

I got that error:

SyntaxError: keyword argument repeated

then after some search I tried given answer here:

records = A.objects.filter(
             a_field = "form_given_value_1",
             B__b_field__c_field__d_field = form_given_value_2
          )

It doesn't give me errors but it doesn't give records also!..

how to achieve that approach ?

Poula Adel · Accepted Answer · 2020-04-26 06:44:02Z

0

First you need to check if form_given_value_* is null because if any is equal to null (no input) the filter() will return nothing

Second after check you need to pass filters to filter() upon your check

We achieve that like below:

    from django.db.models import Q

    filters = Q()
    if form_given_value_1:
        filters &= Q(a_field = "form_given_value_1",)
    if form_given_value_2:
        filters &= Q(B__b_field__c_field__d_field = form_given_value_2,)

    records = A.objects.filter(filters)

edited Apr 26, 2020 at 6:44

answered Apr 25, 2020 at 15:20

Poula Adel

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