Fixed #34255 -- Made PostgreSQL backend use client-side parameters binding with psycopg version 3.

Thanks Guillaume Andreu Sabater for the report.

Co-authored-by: Florian Apolloner <apollo13@users.noreply.github.com>

django/db/backends/mysql/features.py

@@ -144,6 +144,16 @@ class DatabaseFeatures(BaseDatabaseFeatures):
                     },
                 }
             )
+        if "ONLY_FULL_GROUP_BY" in self.connection.sql_mode:
+            skips.update(
+                {
+                    "GROUP BY cannot contain nonaggregated column when "
+                    "ONLY_FULL_GROUP_BY mode is enabled on MySQL, see #34262.": {
+                        "aggregation.tests.AggregateTestCase."
+                        "test_group_by_nested_expression_with_params",
+                    },
+                }
+            )
         return skips
 
     @cached_property

django/db/backends/postgresql/base.py

@@ -223,6 +223,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
         conn_params.pop("assume_role", None)
         conn_params.pop("isolation_level", None)
+        conn_params.pop("server_side_binding", None)
         if settings_dict["USER"]:
             conn_params["user"] = settings_dict["USER"]
         if settings_dict["PASSWORD"]:
@@ -268,7 +269,13 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         connection = self.Database.connect(**conn_params)
         if set_isolation_level:
             connection.isolation_level = self.isolation_level
-        if not is_psycopg3:
+        if is_psycopg3:
+            connection.cursor_factory = (
+                ServerBindingCursor
+                if options.get("server_side_binding") is True
+                else Cursor
+            )
+        else:
             # Register dummy loads() to avoid a round trip from psycopg2's
             # decode to json.dumps() to json.loads(), when using a custom
             # decoder in JSONField.
@@ -436,7 +443,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
 if is_psycopg3:
 
-    class Cursor(Database.Cursor):
+    class CursorMixin:
         """
         A subclass of psycopg cursor implementing callproc.
         """
@@ -457,6 +464,12 @@ if is_psycopg3:
             self.execute(stmt)
             return args
 
+    class ServerBindingCursor(CursorMixin, Database.Cursor):
+        pass
+
+    class Cursor(CursorMixin, Database.ClientCursor):
+        pass
+
     class CursorDebugWrapper(BaseCursorDebugWrapper):
         def copy(self, statement):
             with self.debug_sql(statement):

docs/ref/databases.txt

@@ -117,9 +117,6 @@ PostgreSQL notes
 Django supports PostgreSQL 12 and higher. `psycopg`_ 3.1.8+ or `psycopg2`_
 2.8.4+ is required, though the latest `psycopg`_ 3.1.8+ is recommended.
 
-.. _psycopg: https://www.psycopg.org/psycopg3/
-.. _psycopg2: https://www.psycopg.org/
-
 .. note::
 
     Support for ``psycopg2`` is likely to be deprecated and removed at some
@@ -251,6 +248,31 @@ database configuration in :setting:`DATABASES`::
         },
     }
 
+.. _database-server-side-parameters-binding:
+
+Server-side parameters binding
+------------------------------
+
+.. versionadded:: 4.2
+
+With `psycopg`_ 3.1.8+, Django defaults to the :ref:`client-side binding
+cursors <psycopg:client-side-binding-cursors>`. If you want to use the
+:ref:`server-side binding <psycopg:server-side-binding>` set it in the
+:setting:`OPTIONS` part of your database configuration in
+:setting:`DATABASES`::
+
+    DATABASES = {
+        "default": {
+            "ENGINE": "django.db.backends.postgresql",
+            # ...
+            "OPTIONS": {
+                "server_side_binding": True,
+            },
+        },
+    }
+
+This option is ignored with ``psycopg2``.
+
 Indexes for ``varchar`` and ``text`` columns
 --------------------------------------------
 
@@ -373,6 +395,9 @@ non-durable <https://www.postgresql.org/docs/current/non-durability.html>`_.
     a development machine where you can easily restore the entire contents of
     all databases in the cluster.
 
+.. _psycopg: https://www.psycopg.org/psycopg3/
+.. _psycopg2: https://www.psycopg.org/
+
 .. _mariadb-notes:
 
 MariaDB notes

docs/releases/4.2.txt

@@ -254,6 +254,10 @@ Database backends
 * The new ``"assume_role"`` option is now supported in :setting:`OPTIONS` on
   PostgreSQL to allow specifying the :ref:`session role <database-role>`.
 
+* The new ``"server_side_binding"`` option is now supported in
+  :setting:`OPTIONS` on PostgreSQL with ``psycopg`` 3.1.8+ to allow using
+  :ref:`server-side binding cursors <database-server-side-parameters-binding>`.
+
 Decorators
 ~~~~~~~~~~
 

tests/aggregation/tests.py

@@ -34,6 +34,7 @@ from django.db.models.functions import (
     Cast,
     Coalesce,
     Greatest,
+    Least,
     Lower,
     Now,
     Pi,
@@ -1614,6 +1615,20 @@ class AggregateTestCase(TestCase):
         ).annotate(total=Count("*"))
         self.assertEqual(dict(has_long_books_breakdown), {True: 2, False: 3})
 
+    def test_group_by_nested_expression_with_params(self):
+        books_qs = (
+            Book.objects.annotate(greatest_pages=Greatest("pages", Value(600)))
+            .values(
+                "greatest_pages",
+            )
+            .annotate(
+                min_pages=Min("pages"),
+                least=Least("min_pages", "greatest_pages"),
+            )
+            .values_list("least", flat=True)
+        )
+        self.assertCountEqual(books_qs, [300, 946, 1132])
+
     @skipUnlessDBFeature("supports_subqueries_in_group_by")
     def test_aggregation_subquery_annotation_related_field(self):
         publisher = Publisher.objects.create(name=self.a9.name, num_awards=2)

tests/backends/postgresql/tests.py

@@ -277,6 +277,25 @@ class Tests(TestCase):
         finally:
             new_connection.close()
 
+    @unittest.skipUnless(is_psycopg3, "psycopg3 specific test")
+    def test_connect_server_side_binding(self):
+        """
+        The server-side parameters binding role can be enabled with DATABASES
+        ["OPTIONS"]["server_side_binding"].
+        """
+        from django.db.backends.postgresql.base import ServerBindingCursor
+
+        new_connection = connection.copy()
+        new_connection.settings_dict["OPTIONS"]["server_side_binding"] = True
+        try:
+            new_connection.connect()
+            self.assertEqual(
+                new_connection.connection.cursor_factory,
+                ServerBindingCursor,
+            )
+        finally:
+            new_connection.close()
+
     def test_connect_no_is_usable_checks(self):
         new_connection = connection.copy()
         try: