Remove orphaned label links

On GitLab.com, there are over 2 million orphaned label links out of
a total of 13 million. These orphaned label links can cause
quiet failures, such as unexpected nil values in ExportCsvWorker.

Closes gitlab-org/gitlab-ee#7482

1 files changed, 40 insertions, 0 deletions

diff --git a/spec/migrations/remove_orphaned_label_links_spec.rb b/spec/migrations/remove_orphaned_label_links_spec.rb
new file mode 100644
index 00000000000..13b8919343e
--- /dev/null
+++ b/spec/migrations/remove_orphaned_label_links_spec.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20180906051323_remove_orphaned_label_links.rb')
+
+describe RemoveOrphanedLabelLinks, :migration do
+  let(:label_links) { table(:label_links) }
+  let(:labels) { table(:labels) }
+
+  let(:project) { create(:project) } # rubocop:disable RSpec/FactoriesInMigrationSpecs
+  let(:label) { create_label }
+
+  context 'add foreign key on label_id' do
+    let!(:label_link_with_label) { create_label_link(label_id: label.id) }
+    let!(:label_link_without_label) { create_label_link(label_id: nil) }
+
+    it 'removes orphaned labels without corresponding label' do
+      expect { migrate! }.to change { LabelLink.count }.from(2).to(1)
+    end
+
+    it 'does not remove entries with valid label_id' do
+      expect { migrate! }.not_to change { label_link_with_label.reload }
+    end
+  end
+
+  def create_label(**opts)
+    labels.create!(
+      project_id: project.id,
+      **opts
+    )
+  end
+
+  def create_label_link(**opts)
+    label_links.create!(
+      target_id: 1,
+      target_type: 'Issue',
+      **opts
+    )
+  end
+end