Fixed #21604 -- Embed raw queries as subqueries

Added functionallity so RawQueries can be used as subquries when using __in filter

django/db/models/query.py

@@ -2048,6 +2048,9 @@ class RawQuerySet:
         model_init_names = [f.attname for f in model_init_fields]
         return model_init_names, model_init_order, annotation_fields
 
+    def resolve_expression(self, *args, **kwargs):
+        return self.query.resolve_expression(self, *args, **kwargs)
+
     def prefetch_related(self, *lookups):
         """Same as QuerySet.prefetch_related()"""
         clone = self._clone()

django/db/models/sql/query.py

@@ -82,6 +82,11 @@ JoinInfo = namedtuple(
 class RawQuery:
     """A single raw SQL query."""
 
+    has_select_fields = True
+    contains_aggregate = []
+    contains_over_clause = False
+    subquery = False
+
     def __init__(self, sql, using, params=()):
         self.params = params
         self.sql = sql
@@ -98,7 +103,9 @@ class RawQuery:
         return self.clone(using)
 
     def clone(self, using):
-        return RawQuery(self.sql, using, params=self.params)
+        query = RawQuery(self.sql, using, params=self.params)
+        query.subquery = self.subquery
+        return query
 
     def get_columns(self):
         if self.cursor is None:
@@ -151,6 +158,17 @@ class RawQuery:
         self.cursor = connection.cursor()
         self.cursor.execute(self.sql, params)
 
+    def as_sql(self, compiler, connection):
+        sql = self.sql
+        if self.subquery:
+            sql = "(%s)" % sql
+        return sql, self.params
+
+    def resolve_expression(self, query, *args, **kwargs):
+        clone = self.clone(self.using)
+        clone.subquery = True
+        return clone
+
 
 ExplainInfo = namedtuple("ExplainInfo", ("format", "options"))
 
@@ -1243,7 +1261,7 @@ class Query(BaseExpression):
                 )
             elif hasattr(value, "_meta"):
                 self.check_query_object_type(value, opts, field)
-            elif hasattr(value, "__iter__"):
+            elif hasattr(value, "__iter__") and not getattr(value, "subquery", False):
                 for v in value:
                     self.check_query_object_type(v, opts, field)
 

docs/releases/4.2.txt

@@ -355,6 +355,9 @@ Miscellaneous
 * The undocumented ``negated`` parameter of the
   :class:`~django.db.models.Exists` expression is removed.
 
+* Add functionality so :class:`~django.db.models.sql.RawQuery`
+  can be used as a subquery.
+
 .. _deprecated-features-4.2:
 
 Features deprecated in 4.2

tests/raw_query/tests.py

@@ -3,6 +3,7 @@ from decimal import Decimal
 
 from django.core.exceptions import FieldDoesNotExist
 from django.db.models.query import RawQuerySet
+from django.db.models.sql.query import RawQuery
 from django.test import TestCase, skipUnlessDBFeature
 
 from .models import (
@@ -62,6 +63,12 @@ class RawQueryTests(TestCase):
             paperback=True,
             opening_line="It was the day my grandmother exploded.",
         )
+        cls.b5 = Book.objects.create(
+            title="Some other awesome book",
+            author=cls.a4,
+            paperback=True,
+            opening_line="Story of the book that was left behind",
+        )
         cls.c1 = Coffee.objects.create(brand="dunkin doughnuts")
         cls.c2 = Coffee.objects.create(brand="starbucks")
         cls.r1 = Reviewer.objects.create()
@@ -308,7 +315,7 @@ class RawQueryTests(TestCase):
             ("book_count", 3),
             ("book_count", 0),
             ("book_count", 1),
-            ("book_count", 0),
+            ("book_count", 1),
         )
         authors = Author.objects.order_by("pk")
         self.assertSuccessfulRawQuery(Author, query, authors, expected_annotations)
@@ -413,7 +420,18 @@ class RawQueryTests(TestCase):
         )
 
     def test_len(self):
-        self.assertEqual(len(Book.objects.raw("SELECT * FROM raw_query_book")), 4)
+        self.assertEqual(len(Book.objects.raw("SELECT * FROM raw_query_book")), 5)
         self.assertEqual(
             len(Book.objects.raw("SELECT * FROM raw_query_book WHERE id = 0")), 0
         )
+
+    def test_as_subquery(self):
+        author_id_sub_query = RawQuery(
+            "SELECT id FROM raw_query_author WHERE last_name LIKE %s",
+            using="default",
+            params=["Smith"],
+        )
+        with self.assertNumQueries(1):
+            self.assertEqual(
+                len(Book.objects.filter(author_id__in=author_id_sub_query)), 4
+            )