Fixed code based on review comments

Used existing scope in issuable concern file.
Cleaned up issuable spec file.

app/finders/issuable_finder.rb

@@ -578,17 +578,15 @@ class IssuableFinder
   # rubocop: enable CodeReuse/ActiveRecord
 
   def by_release(items)
-    if releases?
-      items = if filter_by_no_release?
-                items.without_release
-              elsif filter_by_any_release?
-                items.any_release
-              else
-                items.with_release(params[:release_tag])
-              end
-    end
+    return items unless releases?
 
-    items
+    if filter_by_no_release?
+      items.without_release
+    elsif filter_by_any_release?
+      items.any_release
+    else
+      items.with_release(params[:release_tag])
+    end
   end
 
   def filter_by_no_milestone?

app/models/concerns/issuable.rb

@@ -124,18 +124,16 @@ module Issuable
     scope :order_milestone_due_asc,  -> { left_joins_milestones.reorder(Arel.sql('milestones.due_date IS NULL, milestones.id IS NULL, milestones.due_date ASC')) }
 
     scope :without_release, -> do
-      joins("LEFT OUTER JOIN milestones AS ms ON #{table_name}.milestone_id = ms.id
-             LEFT OUTER JOIN milestone_releases AS ms_rl ON ms.id = ms_rl.milestone_id"
-           ).where('ms_rl.release_id IS NULL')
+      left_joins_milestones
+        .joins("LEFT OUTER JOIN milestone_releases ON milestones.id = milestone_releases.milestone_id")
+        .where('milestone_releases.release_id IS NULL')
     end
 
     scope :left_joins_milestones_joins_releases, -> do
-      joins("LEFT OUTER JOIN milestones AS ms
-              JOIN milestone_releases
-                JOIN releases ON milestone_releases.release_id = releases.id
-              ON ms.id = milestone_releases.milestone_id
-            ON #{table_name}.milestone_id = ms.id"
-           ).where('milestone_releases.release_id IS NOT NULL').distinct
+      left_joins_milestones
+        .joins("JOIN milestone_releases ON milestones.id = milestone_releases.milestone_id
+                JOIN releases ON milestone_releases.release_id = releases.id")
+        .where('milestone_releases.release_id IS NOT NULL').distinct
     end
 
     scope :without_label, -> { joins("LEFT OUTER JOIN label_links ON label_links.target_type = '#{name}' AND label_links.target_id = #{table_name}.id").where(label_links: { id: nil }) }

spec/models/concerns/issuable_spec.rb

@@ -853,35 +853,6 @@ describe Issuable do
     end
   end
 
-  # Testing the release related scopes with the following setup:
-  # - release_1
-  #   - milestone_1
-  #     - issue_1
-  #     - issue_2
-  #   - milestone_2
-  #     - issue_3
-  #
-  # - release_2
-  #   - milestone_2
-  #     - issue_3
-  #   - milestone_3
-  #     - (no issue)
-  #
-  # - release_3
-  #   - milestone_4
-  #     - issue_4
-  #   - milestone_5
-  #     - issue_4
-  #
-  # - release_4
-  #   - milestone_3
-  #     - (no issue)
-  #
-  # - milestone_6 (no release)
-  #   - issue_5
-  #
-  # - issue_6 (no milestone, no release)
-
   describe 'release scopes' do
     let_it_be(:project) { create(:project) }
 
@@ -890,35 +861,22 @@ describe Issuable do
     let_it_be(:release_3) { create(:release, tag: 'v3.0', project: project) }
     let_it_be(:release_4) { create(:release, tag: 'v4.0', project: project) }
 
-    let_it_be(:milestone_1) { create(:milestone, title: 'm1', project: project) }
-    let_it_be(:milestone_2) { create(:milestone, title: 'm2', project: project) }
-    let_it_be(:milestone_3) { create(:milestone, title: 'm3', project: project) }
-    let_it_be(:milestone_4) { create(:milestone, title: 'm4', project: project) }
-    let_it_be(:milestone_5) { create(:milestone, title: 'm5', project: project) }
+    let_it_be(:milestone_1) { create(:milestone, releases: [release_1], title: 'm1', project: project) }
+    let_it_be(:milestone_2) { create(:milestone, releases: [release_1, release_2], title: 'm2', project: project) }
+    let_it_be(:milestone_3) { create(:milestone, releases: [release_2, release_4], title: 'm3', project: project) }
+    let_it_be(:milestone_4) { create(:milestone, releases: [release_3], title: 'm4', project: project) }
+    let_it_be(:milestone_5) { create(:milestone, releases: [release_3], title: 'm5', project: project) }
     let_it_be(:milestone_6) { create(:milestone, title: 'm6', project: project) }
 
-    let_it_be(:issue_1) { create(:issue, project: project) }
-    let_it_be(:issue_2) { create(:issue, project: project) }
-    let_it_be(:issue_3) { create(:issue, project: project) }
-    let_it_be(:issue_4) { create(:issue, project: project) }
-    let_it_be(:issue_5) { create(:issue, project: project) }
+    let_it_be(:issue_1) { create(:issue, milestone: milestone_1, project: project) }
+    let_it_be(:issue_2) { create(:issue, milestone: milestone_1, project: project) }
+    let_it_be(:issue_3) { create(:issue, milestone: milestone_2, project: project) }
+    let_it_be(:issue_4) { create(:issue, milestone: milestone_5, project: project) }
+    let_it_be(:issue_5) { create(:issue, milestone: milestone_6, project: project) }
     let_it_be(:issue_6) { create(:issue, project: project) }
 
     let_it_be(:items) { Issue.all }
 
-    before(:all) do
-      milestone_1.issues = [issue_1, issue_2]
-      milestone_2.issues = [issue_3]
-      milestone_4.issues = [issue_4]
-      milestone_5.issues = [issue_4]
-      milestone_6.issues = [issue_5]
-
-      release_1.milestones = [milestone_1, milestone_2]
-      release_2.milestones = [milestone_2, milestone_3]
-      release_3.milestones = [milestone_4, milestone_5]
-      release_4.milestones = [milestone_3]
-    end
-
     describe '#without_release' do
       it 'returns the issues not tied to any milestone and the ones tied to milestone with no release' do
         expect(items.without_release).to contain_exactly(issue_5, issue_6)
@@ -954,19 +912,13 @@ describe Issuable do
         end
       end
 
-      context 'when an issue is tied to multiple milestones under the same release' do
-        it 'returns this issue only once' do
-          expect(items.with_release('v3.0')).to contain_exactly(issue_4)
-        end
-      end
-
       context 'when there is no issue under a specific release' do
         it 'returns no issue' do
           expect(items.with_release('v4.0')).to be_empty
         end
       end
 
-      context 'when a non-existant release tag is passed in' do
+      context 'when a non-existent release tag is passed in' do
         it 'returns no issue' do
           expect(items.with_release('v999.0')).to be_empty
         end