id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36109	Three or more stacked FilteredRelations can create a RecursionError	Peter DeVita	Peter DeVita	"Example test case, this belongs to FilteredRelationTests

{{{
    def test_three_level_nested_chained_relations(self):
        borrower1 = Borrower.objects.create(name=""Jenny"")
        # borrower 1 reserves, rents, and returns book1.
        Reservation.objects.create(
            borrower=borrower1,
            book=self.book1,
            state=Reservation.STOPPED,
        )
        qs = (
            Author.objects.annotate(
                my_books=FilteredRelation(
                    ""book""
                ),
                my_reserved_books=FilteredRelation(
                    ""my_books__reservation"",
                    condition=Q(my_books__reservation__state=Reservation.STOPPED)
                ),
                my_readers=FilteredRelation(
                    ""my_reserved_books__borrower"",
                    condition=Q(my_reserved_books__borrower=borrower1)
                )
            )
        )
        qs = qs.filter(
            my_readers=borrower1
        )
        self.assertQuerySetEqual(
            qs,
            [
                (""Alice"",)
            ],
            lambda x: (x.name,),
        )
}}}

This will result in a {{{RecursionError}}} when the filter is applied. From what I can understand, this is because on {{{Query}}} when it gets to {{{setup_joins}}} and attempts to setup the join for the {{{my_readers}}} FilteredRelation, it is not allowed to reuse the aliases from the first two `FilteredRelation`s. It then constantly recurses, trying to setup the joins and then not being able to reuse the joins.

I'm no ORM expert but the fix might be as simple as just adding the FilteredRelation's join alias to the {{{can_reuse}}} set. Any joins that were going to that table but not through the FilteredRelation should be unaffected since they weren't going to reference its alias anyways. Any joins that do reference that FilteredRelation should always want to reuse this too. The fix is in my diff/PR and tests all pass with it.

This bug might also be only because we're filtering on the last join in the set as the first filter condition, it might be possible to force the aliases to be reusable if you filtered one at a time on each FilteredRelation leading up to it.
"	Bug	closed	Database layer (models, ORM)	5.1	Normal	fixed	FilteredRelation		Ready for checkin	1	0	0	0	0	0