GroupFilterSet to reduce inner joins for performance.

group_filter_set.py

from django.db.models import Q
from django.db.models.constants import LOOKUP_SEP
from django_filters import rest_framework as django_filters
from django_filters.constants import EMPTY_VALUES


class GroupFilterSet(django_filters.FilterSet):
    def filter_queryset(self, queryset):
        """
        Group the fitlers by the first join table to
        reduce inner join queries for performance.
        This would avoid filter chaining like:
        `Model.objects.filter(table_foo__id__in=[xx,xx]).filter(table_foo__name__in=[xx,xx])`
        Instead, it would be grouped as:
        `Model.objects.filter(table_foo__id__in=[xx,xx], table_foo__name__in=[xx,xx])`

        Inspired by discussion at:
        https://github.com/carltongibson/django-filter/issues/745
        https://github.com/carltongibson/django-filter/pull/1167
        """
        groups = {}
        is_distincted = False
        for name, value in self.form.cleaned_data.items():
            if value in EMPTY_VALUES:
                continue
            f = self.filters[name]
            # Do not merge Qs for customized filter method due to complexity.
            if f._method or not f.__class__.filter == django_filters.Filter.filter:
                queryset = self.filters[name].filter(queryset, value)
                continue
            # Use the joined table name as key
            group_name = f.field_name.split(LOOKUP_SEP)[0]
            q = Q(**{LOOKUP_SEP.join([f.field_name, f.lookup_expr]): value})
            if f.exclude:
                q = ~q
            # Check if there's any join query with the same table
            if group_name in groups:
                groups[group_name] = groups[group_name] & q
            else:
                groups[group_name] = q
            if f.distinct:
                is_distincted = True
        for q in groups.values():
            queryset = queryset.filter(q)
        if is_distincted:
            queryset = queryset.distinct()
        return queryset