Fixed #22496: Data migrations get transactions again!

3 files changed, 21 insertions, 3 deletions

diff --git a/django/db/migrations/migration.py b/django/db/migrations/migration.py
index 3d7f47f0fa..708de5393d 100644
--- a/django/db/migrations/migration.py
+++ b/django/db/migrations/migration.py
@@ -1,4 +1,5 @@
 from __future__ import unicode_literals
+from django.db.transaction import atomic
 
 
 class Migration(object):
@@ -97,7 +98,13 @@ class Migration(object):
             new_state = project_state.clone()
             operation.state_forwards(self.app_label, new_state)
             # Run the operation
-            operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
+            if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
+                # We're forcing a transaction on a non-transactional-DDL backend
+                with atomic(schema_editor.connection.alias):
+                    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
+            else:
+                # Normal behaviour
+                operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
             # Switch states
             project_state = new_state
         return project_state
@@ -129,7 +136,13 @@ class Migration(object):
         # Now run them in reverse
         to_run.reverse()
         for operation, to_state, from_state in to_run:
-            operation.database_backwards(self.app_label, schema_editor, from_state, to_state)
+            if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
+                # We're forcing a transaction on a non-transactional-DDL backend
+                with atomic(schema_editor.connection.alias):
+                    operation.database_backwards(self.app_label, schema_editor, from_state, to_state)
+            else:
+                # Normal behaviour
+                operation.database_backwards(self.app_label, schema_editor, from_state, to_state)
         return project_state
 
 
diff --git a/django/db/migrations/operations/base.py b/django/db/migrations/operations/base.py
index 7e93fb7836..d0ab0a39ad 100644
--- a/django/db/migrations/operations/base.py
+++ b/django/db/migrations/operations/base.py
@@ -24,6 +24,10 @@ class Operation(object):
     # Can this migration be represented as SQL? (things like RunPython cannot)
     reduces_to_sql = True
 
+    # Should this operation be forced as atomic even on backends with no
+    # DDL transaction support (i.e., does it have no DDL, like RunPython)
+    atomic = False
+
     serialization_expand_args = []
 
     def __new__(cls, *args, **kwargs):
diff --git a/django/db/migrations/operations/special.py b/django/db/migrations/operations/special.py
index a80096cb32..b7ffbbbd29 100644
--- a/django/db/migrations/operations/special.py
+++ b/django/db/migrations/operations/special.py
@@ -86,7 +86,8 @@ class RunPython(Operation):
 
     reduces_to_sql = False
 
-    def __init__(self, code, reverse_code=None):
+    def __init__(self, code, reverse_code=None, atomic=True):
+        self.atomic = atomic
         # Forwards code
         if not callable(code):
             raise ValueError("RunPython must be supplied with a callable")