1 files changed, 43 insertions, 0 deletions
diff --git a/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb b/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb
new file mode 100644
index 00000000000..88a9f5f8256
--- /dev/null
+++ b/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb
@@ -0,0 +1,43 @@
+class AddUniqueConstraintToProjectFeaturesProjectId < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class ProjectFeature < ActiveRecord::Base
+    self.table_name = 'project_features'
+
+    include EachBatch
+  end
+
+  def up
+    remove_duplicates
+
+    add_concurrent_index :project_features, :project_id, unique: true, name: 'index_project_features_on_project_id_unique'
+    remove_concurrent_index_by_name :project_features, 'index_project_features_on_project_id'
+    rename_index :project_features, 'index_project_features_on_project_id_unique', 'index_project_features_on_project_id'
+  end
+
+  def down
+    rename_index :project_features, 'index_project_features_on_project_id', 'index_project_features_on_project_id_old'
+    add_concurrent_index :project_features, :project_id
+    remove_concurrent_index_by_name :project_features, 'index_project_features_on_project_id_old'
+  end
+
+  private
+
+  def remove_duplicates
+    features = ProjectFeature
+               .select('MAX(id) AS max, COUNT(id), project_id')
+               .group(:project_id)
+               .having('COUNT(id) > 1')
+
+    features.each do |feature|
+      ProjectFeature
+        .where(project_id: feature['project_id'])
+        .where('id <> ?', feature['max'])
+        .each_batch { |batch| batch.delete_all }
+    end
+  end
+end