#36682: RecursionError when traversing several reverse relations with
FilteredRelation
-------------------------------------+-------------------------------------
Reporter: REGNIER Guillaume | Owner: (none)
Type: Bug | Status: new
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: FilteredRelation | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by REGNIER Guillaume:
Old description:
> When declaring a filtered relation with a condition on the 2-distant
> reverse relation, query compilation fails with a RecursionError
>
> === Steps to Reproduce:
> {{{#!python
> class Company(models.Model):
> pass
>
> class Employee(models.Model):
> company = models.ForeignKey(Company, on_delete=models.CASCADE,
> related_name="employees")
>
> class Mission(models.Model):
> employee = models.ForeignKey(Employee, on_delete=models.CASCADE,
> related_name="missions")
> name = models.TextField()
> deadline = models.DateTimeField()
> }}}
>
> {{{#!python
> qs = Company.objects.alias(
> specific_mission=FilteredRelation(
> "employees__missions",
> condition=Q(employees__missions__name="specific"),
> )
> )
> qs = qs.filter(specific_mission__deadline__lt=localtime())
> list(qs)
> }}}
>
> === Expected Behavior:
> `.filter(...)` does not throw RecursionError and produce an SQL query
> equivalent to
> {{{#!sql
> SELECT
> "company"."id"
> FROM
> "company"
> INNER JOIN "employee" ON (
> "company"."id" = "employee"."company_id"
> )
> INNER JOIN "mission" specific_mission ON (
> "employee"."id" = specific_mission."employee_id"
> AND specific_mission."name" = 'specific'
> )
> WHERE
> specific_mission."deadline" < '2025-10-23 11:07:06.224821+02:00'
> }}}
>
> === Actual Behavior:
> `.filter(...)` throws RecursionError
>
> === Analysis:
> My understanding `Query.join()` fails to reuse the join for first reverse
> relation, leading to the `FilteredRelation` being resolved again and
> again.
> Loop is:
> - `FilteredRelation.resolve_expression()`
> - `Query.build_filter()`
> - `Query._add_q()`
> - `Query.build_filter()`
> - `Query.setup_joins()`
> - `Query.join()`
> - `FilteredRelation.resolve_expression()`
>
> === Workaround:
> {{{#!python
> qs = Company.objects.alias(
> _employees=FilteredRelation("employees"),
> specific_mission=FilteredRelation(
> "_employees__missions",
> condition=Q(_employees__missions__name="specific"),
> ),
> )
> qs = qs.filter(specific_mission__deadline__lt=localtime())
> list(qs)
> }}}
>
> === Related tickets:
> #36109: Related to `FilteredRelation` and `RecursionError` (uses
> mentioned workaround)
> #34957: Probably the same underlying issue, ticket was closed due to
> lacks reproduction details
New description:
When declaring a filtered relation with a condition on the 2-distant
reverse relation, query compilation fails with a RecursionError
=== Steps to Reproduce:
{{{#!python
class Company(models.Model):
pass
class Employee(models.Model):
company = models.ForeignKey(Company, on_delete=models.CASCADE,
related_name="employees")
class Mission(models.Model):
employee = models.ForeignKey(Employee, on_delete=models.CASCADE,
related_name="missions")
name = models.TextField()
deadline = models.DateTimeField()
}}}
{{{#!python
qs = Company.objects.alias(
specific_mission=FilteredRelation(
"employees__missions",
condition=Q(employees__missions__name="specific"),
)
)
qs = qs.filter(specific_mission__deadline__lt=localtime())
list(qs)
}}}
=== Expected Behavior:
`.filter(...)` does not throw RecursionError and produce an SQL query
equivalent to
{{{#!sql
SELECT
"company"."id"
FROM
"company"
INNER JOIN "employee" ON (
"company"."id" = "employee"."company_id"
)
INNER JOIN "mission" specific_mission ON (
"employee"."id" = specific_mission."employee_id"
AND specific_mission."name" = 'specific'
)
WHERE
specific_mission."deadline" < '2025-10-23 11:07:06.224821+02:00'
}}}
=== Actual Behavior:
`.filter(...)` throws RecursionError
=== Analysis:
My understanding is that `Query.join()` fails to reuse the join for the
first reverse relation, leading to the `FilteredRelation` being resolved
again and again.
Loop is:
- `FilteredRelation.resolve_expression()`
- `Query.build_filter()`
- `Query._add_q()`
- `Query.build_filter()`
- `Query.setup_joins()`
- `Query.join()`
- `FilteredRelation.resolve_expression()`
=== Workaround:
{{{#!python
qs = Company.objects.alias(
_employees=FilteredRelation("employees"),
specific_mission=FilteredRelation(
"_employees__missions",
condition=Q(_employees__missions__name="specific"),
),
)
qs = qs.filter(specific_mission__deadline__lt=localtime())
list(qs)
}}}
=== Related tickets:
#36109: Related to `FilteredRelation` and `RecursionError` (uses mentioned
workaround)
#34957: Probably the same underlying issue, ticket was closed due to lacks
reproduction details
--
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Ticket URL: <https://code.djangoproject.com/ticket/36682#comment:2>
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