#33262: Aggregate filtered by an Exists subquery crashes
-------------------------------------+-------------------------------------
               Reporter:  Hannes     |          Owner:  Hannes Ljungberg
  Ljungberg                          |
                   Type:  Bug        |         Status:  assigned
              Component:  Database   |        Version:  dev
  layer (models, ORM)                |
               Severity:  Normal     |       Keywords:
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 For example:
 {{{
 Book.objects.values("publisher").aggregate(
     max_rating=Max(
         "rating",
         filter=Exists(
             Book.authors.through.objects.filter(book=OuterRef("pk")),
         ),
     )
 }}}

 Will crash with the following traceback:
 {{{
 Traceback (most recent call last):
   File "/tests/django/tests/aggregation/test_filter_argument.py", line
 146, in test_filtered_aggregate_with_exists
     aggregate = Book.objects.values('publisher').aggregate(
   File "/tests/django/django/db/models/query.py", line 405, in aggregate
     return query.get_aggregation(self.db, kwargs)
   File "/tests/django/django/db/models/sql/query.py", line 501, in
 get_aggregation
     result = compiler.execute_sql(SINGLE)
   File "/tests/django/django/db/models/sql/compiler.py", line 1189, in
 execute_sql
     sql, params = self.as_sql()
   File "/tests/django/django/db/models/sql/compiler.py", line 531, in
 as_sql
     extra_select, order_by, group_by = self.pre_sql_setup()
   File "/tests/django/django/db/models/sql/compiler.py", line 59, in
 pre_sql_setup
     self.setup_query()
   File "/tests/django/django/db/models/sql/compiler.py", line 50, in
 setup_query
     self.select, self.klass_info, self.annotation_col_map =
 self.get_select()
   File "/tests/django/django/db/models/sql/compiler.py", line 267, in
 get_select
     sql, params = self.compile(col)
   File "/tests/django/django/db/models/sql/compiler.py", line 463, in
 compile
     sql, params = node.as_sql(self, self.connection)
   File "/tests/django/django/db/models/aggregates.py", line 90, in as_sql
     return sql, params + filter_params
 TypeError: can only concatenate list (not "tuple") to list
 }}}

 The following patch should fix the issue:
 {{{
 diff --git a/django/db/models/aggregates.py
 b/django/db/models/aggregates.py
 index 596a161669..8c4eae7906 100644
 --- a/django/db/models/aggregates.py
 +++ b/django/db/models/aggregates.py
 @@ -87,7 +87,7 @@ class Aggregate(Func):
                      compiler, connection, template=template,
 filter=filter_sql,
                      **extra_context
                  )
 -                return sql, params + filter_params
 +                return sql, (*params, *filter_params)
              else:
                  copy = self.copy()
                  copy.filter = None
 }}}

-- 
Ticket URL: <https://code.djangoproject.com/ticket/33262>
Django <https://code.djangoproject.com/>
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