1 files changed, 35 insertions, 0 deletions
diff --git a/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb b/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb
new file mode 100644
index 00000000000..75a3eb15124
--- /dev/null
+++ b/db/migrate/20160725104020_merge_request_diff_remove_uniq.rb
@@ -0,0 +1,35 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MergeRequestDiffRemoveUniq < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+  disable_ddl_transaction!
+
+  DOWNTIME = false
+
+  def up
+    constraint_name = 'merge_request_diffs_merge_request_id_key'
+
+    transaction do
+      if index_exists?(:merge_request_diffs, :merge_request_id)
+        remove_index(:merge_request_diffs, :merge_request_id)
+      end
+
+      # In some bizarre cases PostgreSQL might have a separate unique constraint
+      # that we'll need to drop.
+      if constraint_exists?(constraint_name) && Gitlab::Database.postgresql?
+        execute("ALTER TABLE merge_request_diffs DROP CONSTRAINT IF EXISTS #{constraint_name};")
+      end
+    end
+  end
+
+  def down
+    unless index_exists?(:merge_request_diffs, :merge_request_id)
+      add_concurrent_index(:merge_request_diffs, :merge_request_id, unique: true)
+    end
+  end
+
+  def constraint_exists?(name)
+    indexes(:merge_request_diffs).map(&:name).include?(name)
+  end
+end