Refactor new undo_* methods

- Move code for creating a new column from old into a function so that
it can be reused.
- Also add comments above the methods.

1 files changed, 2 insertions, 2 deletions

diff --git a/doc/development/what_requires_downtime.md b/doc/development/what_requires_downtime.md
index f4cee410066..00371057d3c 100644
--- a/doc/development/what_requires_downtime.md
+++ b/doc/development/what_requires_downtime.md
@@ -88,7 +88,7 @@ class RenameUsersUpdatedAtToUpdatedAtTimestamp < ActiveRecord::Migration[4.2]
   end
 
   def down
-    cleanup_concurrent_column_rename :users, :updated_at_timestamp, :updated_at
+    undo_rename_column_concurrently :users, :updated_at, :updated_at_timestamp
   end
 end
 ```
@@ -118,7 +118,7 @@ class CleanupUsersUpdatedAtRename < ActiveRecord::Migration[4.2]
   end
 
   def down
-    rename_column_concurrently :users, :updated_at_timestamp, :updated_at
+    undo_cleanup_concurrent_column_rename :users, :updated_at, :updated_at_timestamp
   end
 end
 ```