Fix pseudo n+1 queries with Note and Note Authors in issuables APIs

This was not a clear cut n+1 query, given that if you're directly subscribed to all issues
that the API is returning you never really need to check for the notes. However, if you're
subscribed to _all_ of them, then for each issuable you need to go once to `notes`, and
once to `users` (for the authors). By preemtively loading notes and authors, at worst you have
1 extra query, and at best you saved 2n extra queries. We also took advantage of this preloading
of notes when counting user notes.

1 files changed, 26 insertions, 0 deletions

diff --git a/spec/models/concerns/issuable_spec.rb b/spec/models/concerns/issuable_spec.rb
index dd03d64f750..efbcbf72f76 100644
--- a/spec/models/concerns/issuable_spec.rb
+++ b/spec/models/concerns/issuable_spec.rb
@@ -10,6 +10,16 @@ describe Issue, "Issuable" do
     it { is_expected.to belong_to(:assignee) }
     it { is_expected.to have_many(:notes).dependent(:destroy) }
     it { is_expected.to have_many(:todos).dependent(:destroy) }
+
+    context 'Notes' do
+      let!(:note) { create(:note, noteable: issue, project: issue.project) }
+      let(:scoped_issue) { Issue.includes(notes: :author).find(issue.id) }
+
+      it 'indicates if the notes have their authors loaded' do
+        expect(issue.notes).not_to be_authors_loaded
+        expect(scoped_issue.notes).to be_authors_loaded
+      end
+    end
   end
 
   describe 'Included modules' do
@@ -245,6 +255,22 @@ describe Issue, "Issuable" do
     end
   end
 
+  describe '#user_notes_count' do
+    let(:project) { create(:project) }
+    let(:issue1) { create(:issue, project: project) }
+    let(:issue2) { create(:issue, project: project) }
+
+    before do
+      create_list(:note, 3, noteable: issue1, project: project)
+      create_list(:note, 6, noteable: issue2, project: project)
+    end
+
+    it 'counts the user notes' do
+      expect(issue1.user_notes_count).to be(3)
+      expect(issue2.user_notes_count).to be(6)
+    end
+  end
+
   describe "votes" do
     let(:project) { issue.project }