[1.8.x] Fixed #26071 -- Fixed crash with __in lookup in a Case expression.

Partial backport of afe0bb7b13bb8dc4370f32225238012c873b0ee3 from master.

2 files changed, 21 insertions, 3 deletions

diff --git a/django/db/models/lookups.py b/django/db/models/lookups.py
index d0b30ace1d..8428d38d65 100644
--- a/django/db/models/lookups.py
+++ b/django/db/models/lookups.py
@@ -92,6 +92,10 @@ class Transform(RegisterLookupMixin):
             bilateral_transforms.append((self.__class__, self.init_lookups))
         return bilateral_transforms
 
+    @cached_property
+    def contains_aggregate(self):
+        return self.lhs.contains_aggregate
+
 
 class Lookup(RegisterLookupMixin):
     lookup_name = None
@@ -194,6 +198,10 @@ class Lookup(RegisterLookupMixin):
     def as_sql(self, compiler, connection):
         raise NotImplementedError
 
+    @cached_property
+    def contains_aggregate(self):
+        return self.lhs.contains_aggregate or getattr(self.rhs, 'contains_aggregate', False)
+
 
 class BuiltinLookup(Lookup):
     def process_lhs(self, compiler, connection, lhs=None):
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 2ba6ceac33..8cad3df9a5 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -315,9 +315,9 @@ class WhereNode(tree.Node):
 
     @classmethod
     def _contains_aggregate(cls, obj):
-        if not isinstance(obj, tree.Node):
-            return getattr(obj.lhs, 'contains_aggregate', False) or getattr(obj.rhs, 'contains_aggregate', False)
-        return any(cls._contains_aggregate(c) for c in obj.children)
+        if isinstance(obj, tree.Node):
+            return any(cls._contains_aggregate(c) for c in obj.children)
+        return obj.contains_aggregate
 
     @cached_property
     def contains_aggregate(self):
@@ -336,6 +336,7 @@ class EverythingNode(object):
     """
     A node that matches everything.
     """
+    contains_aggregate = False
 
     def as_sql(self, compiler=None, connection=None):
         return '', []
@@ -345,11 +346,16 @@ class NothingNode(object):
     """
     A node that matches nothing.
     """
+    contains_aggregate = False
+
     def as_sql(self, compiler=None, connection=None):
         raise EmptyResultSet
 
 
 class ExtraWhere(object):
+    # The contents are a black box - assume no aggregates are used.
+    contains_aggregate = False
+
     def __init__(self, sqls, params):
         self.sqls = sqls
         self.params = params
@@ -410,6 +416,10 @@ class Constraint(object):
 
 
 class SubqueryConstraint(object):
+    # Even if aggregates would be used in a subquery, the outer query isn't
+    # interested about those.
+    contains_aggregate = False
+
     def __init__(self, alias, columns, targets, query_object):
         self.alias = alias
         self.columns = columns