[Answer]-Python – inner join 3 classes

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You could use isnull or any other field lookups to constrain data from A:

q = A.objects.filter(b__isnull=False, b__c__parameter1__isnull=False)

result query will be similar to this:

SELECT "appname_A"."id", "appname_A"."parameter1" FROM "appname_A"
INNER JOIN "appname_B" ON ("appname_A"."id" = "appname_B"."a_id")
INNER JOIN "appname_C" ON ("appname_B"."id" = "appname_C"."b_id")
WHERE ("appname_C"."parameter1" IS NOT NULL AND "appname_B"."id" IS NOT NULL)
ORDER BY "appname_A"."id" ASC

and you should use select_related from C (backwards) if you want to select all data in one query from joined tables:

q = C.objects.filter(b__a__parameter1=SOMETHING).select_related()

result query will start from:

SELECT "appname_C"."id", "appname_C"."parameter1", "appname_C"."b_id",
       "appname_B"."id", "appname_B"."parameter1", "appname_B"."a_id",
       "appname_A"."id", "appname_A"."parameter1"
INNER JOIN ...
👤ndpu

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