Fixed #23514 -- Prevented queries in PostGISOperations init

Thanks Mattia Procopio for the report.

django/contrib/gis/db/backends/postgis/operations.py

@@ -176,10 +176,6 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
             'bboverlaps': PostGISOperator('&&'),
         }
 
-        # Native geometry type support added in PostGIS 2.0.
-        if self.spatial_version >= (2, 0, 0):
-            self.geometry = True
-
         # Creating a dictionary lookup of all GIS terms for PostGIS.
         self.gis_terms = set(['isnull'])
         self.gis_terms.update(self.geometry_operators)
@@ -220,14 +216,33 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
         self.union = prefix + 'Union'
         self.unionagg = prefix + 'Union'
 
+    # Following "attributes" are properties due to the spatial_version check and
+    # to delay database access
+    @property
+    def extent3d(self):
         if self.spatial_version >= (2, 0, 0):
-            self.extent3d = prefix + '3DExtent'
-            self.length3d = prefix + '3DLength'
-            self.perimeter3d = prefix + '3DPerimeter'
+            return self.geom_func_prefix + '3DExtent'
         else:
-            self.extent3d = prefix + 'Extent3D'
-            self.length3d = prefix + 'Length3D'
-            self.perimeter3d = prefix + 'Perimeter3D'
+            return self.geom_func_prefix + 'Extent3D'
+
+    @property
+    def length3d(self):
+        if self.spatial_version >= (2, 0, 0):
+            return self.geom_func_prefix + '3DLength'
+        else:
+            return self.geom_func_prefix + 'Length3D'
+
+    @property
+    def perimeter3d(self):
+        if self.spatial_version >= (2, 0, 0):
+            return self.geom_func_prefix + '3DPerimeter'
+        else:
+            return self.geom_func_prefix + 'Perimeter3D'
+
+    @property
+    def geometry(self):
+        # Native geometry type support added in PostGIS 2.0.
+        return self.spatial_version >= (2, 0, 0)
 
     @cached_property
     def spatial_version(self):

tests/backends/tests.py

@@ -571,6 +571,14 @@ class BackendTestCase(TestCase):
         self.assertTrue(hasattr(connection.ops, 'connection'))
         self.assertEqual(connection, connection.ops.connection)
 
+    def test_database_operations_init(self):
+        """
+        Test that DatabaseOperations initialization doesn't query the database.
+        See #17656.
+        """
+        with self.assertNumQueries(0):
+            connection.ops.__class__(connection)
+
     def test_cached_db_features(self):
         self.assertIn(connection.features.supports_transactions, (True, False))
         self.assertIn(connection.features.supports_stddev, (True, False))