[1.7.x] Fixed removal of GIS column in PostGIS 1.x migration

Refs #22481.
Backport of 2f9d1576e from master, squashed with 2f9d1576e8.

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

@@ -7,6 +7,7 @@ class PostGISSchemaEditor(DatabaseSchemaEditor):
     geom_index_ops_nd = 'GIST_GEOMETRY_OPS_ND'
 
     sql_add_geometry_column = "SELECT AddGeometryColumn(%(table)s, %(column)s, %(srid)s, %(geom_type)s, %(dim)s)"
+    sql_drop_geometry_column = "SELECT DropGeometryColumn(%(table)s, %(column)s)"
     sql_alter_geometry_column_not_null = "ALTER TABLE %(table)s ALTER COLUMN %(column)s SET NOT NULL"
     sql_add_spatial_index = "CREATE INDEX %(index)s ON %(table)s USING %(index_type)s (%(column)s %(ops)s)"
 
@@ -88,3 +89,15 @@ class PostGISSchemaEditor(DatabaseSchemaEditor):
         for sql in self.geometry_sql:
             self.execute(sql)
         self.geometry_sql = []
+
+    def remove_field(self, model, field):
+        from django.contrib.gis.db.models.fields import GeometryField
+        if not isinstance(field, GeometryField) or self.connection.ops.spatial_version > (2, 0):
+            super(PostGISSchemaEditor, self).remove_field(model, field)
+        else:
+            self.execute(
+                self.sql_drop_geometry_column % {
+                    "table": self.geo_quote_name(model._meta.db_table),
+                    "column": self.geo_quote_name(field.column),
+                }
+            )

django/contrib/gis/tests/gis_migrations/test_operations.py

@@ -10,6 +10,11 @@ from django.test import TransactionTestCase
 
 if HAS_SPATIAL_DB:
     from django.contrib.gis.db.models import fields
+    try:
+        from django.contrib.gis.models import GeometryColumns
+        HAS_GEOMETRY_COLUMNS = True
+    except ImportError:
+        HAS_GEOMETRY_COLUMNS = False
 
 
 @skipUnless(HAS_SPATIAL_DB, "Spatial db is required.")
@@ -23,6 +28,9 @@ class OperationTests(TransactionTestCase):
     def assertColumnExists(self, table, column):
         self.assertIn(column, [c.name for c in self.get_table_description(table)])
 
+    def assertColumnNotExists(self, table, column):
+        self.assertNotIn(column, [c.name for c in self.get_table_description(table)])
+
     def apply_operations(self, app_label, project_state, operations):
         migration = Migration('name', app_label)
         migration.operations = operations
@@ -30,6 +38,17 @@ class OperationTests(TransactionTestCase):
             return migration.apply(project_state, editor)
 
     def set_up_test_model(self):
+        # Delete the tables if they already exist
+        with connection.cursor() as cursor:
+            try:
+                cursor.execute("DROP TABLE %s" % connection.ops.quote_name("gis_neighborhood"))
+            except:
+                pass
+            else:
+                if HAS_GEOMETRY_COLUMNS:
+                    cursor.execute("DELETE FROM geometry_columns WHERE %s = %%s" % (
+                        GeometryColumns.table_name_col(),), ["gis_neighborhood"])
+
         operations = [migrations.CreateModel(
             "Neighborhood",
             [
@@ -57,11 +76,27 @@ class OperationTests(TransactionTestCase):
         self.assertColumnExists("gis_neighborhood", "path")
 
         # Test GeometryColumns when available
-        try:
-            from django.contrib.gis.models import GeometryColumns
-        except ImportError:
-            return
-        self.assertEqual(
-            GeometryColumns.objects.filter(**{GeometryColumns.table_name_col(): "gis_neighborhood"}).count(),
-            2
-        )
+        if HAS_GEOMETRY_COLUMNS:
+            self.assertEqual(
+                GeometryColumns.objects.filter(**{GeometryColumns.table_name_col(): "gis_neighborhood"}).count(),
+                2
+            )
+
+    def test_remove_gis_field(self):
+        """
+        Tests the RemoveField operation with a GIS-enabled column.
+        """
+        project_state = self.set_up_test_model()
+        operation = migrations.RemoveField("Neighborhood", "geom")
+        new_state = project_state.clone()
+        operation.state_forwards("gis", new_state)
+        with connection.schema_editor() as editor:
+            operation.database_forwards("gis", editor, project_state, new_state)
+        self.assertColumnNotExists("gis_neighborhood", "geom")
+
+        # Test GeometryColumns when available
+        if HAS_GEOMETRY_COLUMNS:
+            self.assertEqual(
+                GeometryColumns.objects.filter(**{GeometryColumns.table_name_col(): "gis_neighborhood"}).count(),
+                0
+            )