Nested OuterRef can raise AttributeError: 'OuterRef' object has no attribute 'contains_over_clause'

[Pierre-Nicolas Rigal]

Porting our application from Django 3 to 4, we're seeing exception raised in complex queries using nested OuterRef

File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/query.py", line 1436, in filter
    return self._filter_or_exclude(False, args, kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/query.py", line 1454, in _filter_or_exclude
    clone._filter_or_exclude_inplace(negate, args, kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/query.py", line 1461, in _filter_or_exclude_inplace
    self._query.add_q(Q(*args, **kwargs))
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1545, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1576, in _add_q
    child_clause, needed_inner = self.build_filter(
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1435, in build_filter
    value = self.resolve_lookup_value(value, can_reuse, allow_joins)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1204, in resolve_lookup_value
    value = value.resolve_expression(
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/query.py", line 1923, in resolve_expression
    query = self.query.resolve_expression(*args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1145, in resolve_expression
    clone.where.resolve_expression(query, *args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/where.py", line 278, in resolve_expression
    clone._resolve_node(clone, *args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/where.py", line 270, in _resolve_node
    cls._resolve_node(child, query, *args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/where.py", line 274, in _resolve_node
    node.rhs = cls._resolve_leaf(node.rhs, query, *args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/sql/where.py", line 263, in _resolve_leaf
    expr = expr.resolve_expression(query, *args, **kwargs)
  File "/usr/local/filewave/python/lib/python3.10/site-packages/django/db/models/expressions.py", line 862, in resolve_expression
    if col.contains_over_clause:
AttributeError: 'OuterRef' object has no attribute 'contains_over_clause'

Looking at code, the issue seems to be the following:

class ResolvedOuterRef(F):
    """
    An object that contains a reference to an outer query.
 
    In this case, the reference to the outer query has been resolved because
    the inner query has been used as a subquery.
    """
 
    contains_aggregate = False
    contains_over_clause = False
 
    def as_sql(self, *args, **kwargs):
        raise ValueError(
            "This queryset contains a reference to an outer query and may "
            "only be used in a subquery."
        )
 
    def resolve_expression(self, *args, **kwargs):
        col = super().resolve_expression(*args, **kwargs)
        if col.contains_over_clause:
            raise NotSupportedError(
                f"Referencing outer query window expression is not supported: "
                f"{self.name}."
            )

In case of OuterRef(OuterRef( "field" )), col = super().resolve_expression(*args, **kwargs) will use:

class OuterRef(F):
    contains_aggregate = False


    def resolve_expression(self, *args, **kwargs):
        if isinstance(self.name, self.__class__):
            return self.name
        return ResolvedOuterRef(self.name)

so self.name is an OuterRef, then it returns it directly, and then if col.contains_over_clause: fails because col.contains_over_clause is not defined for OuterRef.

Looks like adding col.contains_over_clause=False to class OuterRef solves the issue - or checking if object col.contains_over_clause.