Minor fixes

app/models/concerns/label_eventable.rb

@@ -2,9 +2,7 @@
 
 # == LabelEventable concern
 #
-# Contains functionality related to objects that support adding/removing events.
-#
-# Used by Issue and MergeRequest.
+# Contains functionality related to objects that support adding/removing labels.
 #
 
 module LabelEventable

app/models/resource_label_event.rb

@@ -3,8 +3,6 @@
 class ResourceLabelEvent < ActiveRecord::Base
   prepend EE::ResourceLabelEvent
 
-  ISSUABLE_COLUMNS = %i(issue_id merge_request_id).freeze
-
   belongs_to :user
   belongs_to :issue
   belongs_to :merge_request
@@ -12,28 +10,26 @@ class ResourceLabelEvent < ActiveRecord::Base
 
   validates :user, presence: true, on: :create
   validates :label, presence: true, on: :create
-  validate :issuable_id_is_present
+  validate :exactly_one_issuable
 
   enum action: {
     add: 1,
     remove: 2
   }
 
+  def self.issuable_columns
+    %i(issue_id merge_request_id).freeze
+  end
+
   def issuable
     issue || merge_request
   end
 
   private
 
-  def issuable_columns
-    ISSUABLE_COLUMNS
-  end
-
-  def issuable_id_is_present
-    ids = issuable_columns.find_all {|attr| self[attr]}
-
-    if ids.size != 1
-      errors.add(:base, "Exactly one of #{issuable_columns.join(', ')} is required")
+  def exactly_one_issuable
+    if self.class.issuable_columns.count { |attr| self[attr] } != 1
+      errors.add(:base, "Exactly one of #{self.class.issuable_columns.join(', ')} is required")
     end
   end
 end

app/services/resource_label_event_service.rb

 # frozen_string_literal: true
 
 module ResourceLabelEventService
+  prepend EE::ResourceLabelEventService
+
   extend self
 
   def change_labels(resource, user, added_labels, removed_labels)
@@ -23,9 +25,10 @@ module ResourceLabelEventService
   private
 
   def resource_column(resource)
-    if resource.is_a?(Issue)
+    case resource
+    when Issue
       :issue_id
-    elsif resource.is_a?(MergeRequest)
+    when MergeRequest
       :merge_request_id
     else
       raise ArgumentError, "Unknown resource type #{resource.class.name}"

changelogs/unreleased/jprovazn-resource-events.yml

+---
+title: Add new model for tracking label events.
+merge_request:
+author:
+type: added

ee/app/models/ee/resource_label_event.rb

@@ -5,16 +5,19 @@ module EE
     extend ActiveSupport::Concern
     extend ::Gitlab::Utils::Override
 
-    EE_ISSUABLE_COLUMNS = %i(epic_id).freeze
+    prepended do
+      belongs_to :epic
+    end
+
+    class_methods do
+      def issuable_columns
+        %i(epic_id).freeze + super
+      end
+    end
 
     override :issuable
     def issuable
       epic || super
     end
-
-    override :issuable_columns
-    def issuable_columns
-      EE_ISSUABLE_COLUMNS + super
-    end
   end
 end

ee/app/services/ee/resource_label_event_service.rb

+# frozen_string_literal: true
+
+module EE
+  module ResourceLabelEventService
+    extend ActiveSupport::Concern
+    extend ::Gitlab::Utils::Override
+
+    override :resource_column
+    def resource_column(resource)
+      resource.is_a?(Epic) ? :epic_id : super
+    end
+  end
+end

ee/spec/models/ee/resource_label_event_spec.rb

+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe ResourceLabelEvent, type: :model do
+  subject { build(:resource_label_event) }
+  let(:epic) { create(:epic) }
+
+  describe 'validations' do
+    describe 'Issuable validation' do
+      it 'is valid if only epic_id is set' do
+        subject.attributes = { epic: epic, issue: nil, merge_request: nil }
+
+        expect(subject).to be_valid
+      end
+    end
+  end
+end

spec/services/resource_label_event_service_spec.rb

@@ -11,12 +11,43 @@ describe ResourceLabelEventService do
     subject { described_class.change_labels(resource, author, added, removed) }
 
     let(:labels)  { create_list(:label, 2, project: project) }
-    let(:added)   { [labels[0]] }
-    let(:removed) { [labels[1]] }
 
-    it 'creates an event for each label in single query' do
-      expect(Gitlab::Database).to receive(:bulk_insert).once.and_call_original
-      expect { subject }.to change { resource.resource_label_events.count }.from(0).to(2)
+    def expect_label_event(event, label, action)
+      expect(event.user).to eq(author)
+      expect(event.label).to eq(label)
+      expect(event.action).to eq(action)
+    end
+
+    context 'when adding a label' do
+      let(:added)   { [labels[0]] }
+      let(:removed) { [] }
+
+      it 'creates new label event' do
+        expect { subject }.to change { resource.resource_label_events.count }.from(0).to(1)
+
+        expect_label_event(resource.resource_label_events.first, labels[0], 'add')
+      end
+    end
+
+    context 'when removing a label' do
+      let(:added)   { [] }
+      let(:removed) { [labels[1]] }
+
+      it 'creates new label event' do
+        expect { subject }.to change { resource.resource_label_events.count }.from(0).to(1)
+
+        expect_label_event(resource.resource_label_events.first, labels[1], 'remove')
+      end
+    end
+
+    context 'when both adding and removing labels' do
+      let(:added)   { [labels[0]] }
+      let(:removed) { [labels[1]] }
+
+      it 'creates all label events in a single query' do
+        expect(Gitlab::Database).to receive(:bulk_insert).once.and_call_original
+        expect { subject }.to change { resource.resource_label_events.count }.from(0).to(2)
+      end
     end
   end
 end