Fixed #27056 -- Allowed migrating geometry field dimension on PostGIS

Thanks Tim Graham for the review.

1 files changed, 29 insertions, 0 deletions

diff --git a/django/contrib/gis/db/backends/postgis/schema.py b/django/contrib/gis/db/backends/postgis/schema.py
index 4ee46cb3ff..d88901b50d 100644
--- a/django/contrib/gis/db/backends/postgis/schema.py
+++ b/django/contrib/gis/db/backends/postgis/schema.py
@@ -6,6 +6,9 @@ class PostGISSchemaEditor(DatabaseSchemaEditor):
     geom_index_ops_nd = 'GIST_GEOMETRY_OPS_ND'
     rast_index_wrapper = 'ST_ConvexHull(%s)'
 
+    sql_alter_column_to_3d = "ALTER COLUMN %(column)s TYPE %(type)s USING ST_Force3D(%(column)s)::%(type)s"
+    sql_alter_column_to_2d = "ALTER COLUMN %(column)s TYPE %(type)s USING ST_Force2D(%(column)s)::%(type)s"
+
     def geo_quote_name(self, name):
         return self.connection.ops.geo_quote_name(name)
 
@@ -36,3 +39,29 @@ class PostGISSchemaEditor(DatabaseSchemaEditor):
             "columns": field_column,
             "extra": '',
         }
+
+    def _alter_column_type_sql(self, table, old_field, new_field, new_type):
+        """
+        Special case when dimension changed.
+        """
+        if not hasattr(old_field, 'dim') or not hasattr(new_field, 'dim'):
+            return super(PostGISSchemaEditor, self)._alter_column_type_sql(
+                table, old_field, new_field, new_type
+            )
+
+        if old_field.dim == 2 and new_field.dim == 3:
+            sql_alter = self.sql_alter_column_to_3d
+        elif old_field.dim == 3 and new_field.dim == 2:
+            sql_alter = self.sql_alter_column_to_2d
+        else:
+            sql_alter = self.sql_alter_column_type
+        return (
+            (
+                sql_alter % {
+                    "column": self.quote_name(new_field.column),
+                    "type": new_type,
+                },
+                [],
+            ),
+            [],
+        )