Allow persisting start/due dates and milestone ids

ee/app/models/ee/epic.rb

@@ -111,15 +111,13 @@ module EE
     alias_attribute(:due_date, :end_date)
 
     def update_dates
-      if !start_date_is_fixed? || !due_date_is_fixed?
-        milestone_dates = issues
-          .joins(:milestone)
-          .pluck('MIN(milestones.start_date)', 'MAX(milestones.due_date)')
-          .first
-      end
+      milestone_data = fetch_milestone_date_data
+
+      self.start_date = start_date_is_fixed? ? start_date_fixed : milestone_data[:start_date]
+      self.start_date_sourcing_milestone_id = milestone_data[:start_date_sourcing_milestone_id]
+      self.due_date = due_date_is_fixed? ? due_date_fixed : milestone_data[:due_date]
+      self.due_date_sourcing_milestone_id = milestone_data[:due_date_sourcing_milestone_id]
 
-      self.start_date = start_date_is_fixed? ? start_date_fixed : milestone_dates[0]
-      self.due_date = due_date_is_fixed? ? due_date_fixed : milestone_dates[1]
       save if changed?
     end
 
@@ -179,5 +177,35 @@ module EE
     def compute_due_date
       due_date_is_fixed? ? due_date_fixed : due_date_from_milestones
     end
+
+    def fetch_milestone_date_data
+      sql = <<~SQL
+        SELECT milestones.id, milestones.start_date, milestones.due_date FROM milestones 
+        INNER JOIN issues ON issues.milestone_id = milestones.id
+        INNER JOIN epic_issues ON epic_issues.issue_id = issues.id
+        INNER JOIN (
+          SELECT MIN(milestones.start_date) AS start_date, MAX(milestones.due_date) AS due_date
+          FROM milestones 
+          INNER JOIN issues ON issues.milestone_id = milestones.id
+          INNER JOIN epic_issues ON epic_issues.issue_id = issues.id
+          WHERE epic_issues.epic_id = #{id}
+        ) inner_results ON (inner_results.start_date = milestones.start_date OR inner_results.due_date = milestones.due_date)
+        WHERE epic_issues.epic_id = #{id}
+        ORDER BY milestones.start_date, milestones.due_date;
+      SQL
+
+      db_results = ActiveRecord::Base.connection.select_all(sql).to_a
+
+      results = {}
+      db_results.find { |row| row['start_date'] }&.tap do |row|
+        results[:start_date] = row['start_date']
+        results[:start_date_sourcing_milestone_id] = row['id']
+      end
+      db_results.reverse.find { |row| row['due_date'] }&.tap do |row|
+        results[:due_date] = row['due_date']
+        results[:due_date_sourcing_milestone_id] = row['id']
+      end
+      results
+    end
   end
 end

ee/spec/models/epic_spec.rb

@@ -165,6 +165,7 @@ describe Epic do
 
     context 'fixed date is not set' do
       subject { create(:epic, start_date: nil, end_date: nil) }
+
       let(:milestone1) {
         create(
           :milestone,
@@ -180,18 +181,135 @@ describe Epic do
         )
       }
 
-      before do
-        epic_issue1 = create(:epic_issue, epic: subject)
-        epic_issue1.issue.update(milestone: milestone1)
-        epic_issue2 = create(:epic_issue, epic: subject)
-        epic_issue2.issue.update(milestone: milestone2)
+      context 'multiple milestones' do
+        before do
+          epic_issue1 = create(:epic_issue, epic: subject)
+          epic_issue1.issue.update(milestone: milestone1)
+          epic_issue2 = create(:epic_issue, epic: subject)
+          epic_issue2.issue.update(milestone: milestone2)
+        end
+
+        context 'complete start and due dates' do
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(milestone1.start_date)
+            expect(subject.due_date).to eq(milestone2.due_date)
+          end
+        end
+
+        context 'without due date' do
+          let(:milestone1) {
+            create(
+              :milestone,
+              start_date: Date.new(2000, 1, 1),
+              due_date: nil
+            )
+          }
+          let(:milestone2) {
+            create(
+              :milestone,
+              start_date: Date.new(2000, 1, 3),
+              due_date: nil
+            )
+          }
+
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(milestone1.start_date)
+            expect(subject.due_date).to eq(nil)
+          end
+        end
+
+        context 'without any dates' do
+          let(:milestone1) {
+            create(
+              :milestone,
+              start_date: nil,
+              due_date: nil
+            )
+          }
+          let(:milestone2) {
+            create(
+              :milestone,
+              start_date: nil,
+              due_date: nil
+            )
+          }
+
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(nil)
+            expect(subject.due_date).to eq(nil)
+          end
+        end
       end
 
-      it 'updates to milestone dates' do
-        subject.update_dates
+      context 'without milestone' do
+        before do
+          create(:epic_issue, epic: subject)
+        end
+
+        it 'updates to milestone dates' do
+          subject.update_dates
+
+          expect(subject.start_date).to eq(nil)
+          expect(subject.start_date_sourcing_milestone_id).to eq(nil)
+          expect(subject.due_date).to eq(nil)
+          expect(subject.due_date_sourcing_milestone_id).to eq(nil)
+        end
+      end
 
-        expect(subject.start_date).to eq(milestone1.start_date)
-        expect(subject.due_date).to eq(milestone2.due_date)
+      context 'single milestone' do
+        before do
+          epic_issue1 = create(:epic_issue, epic: subject)
+          epic_issue1.issue.update(milestone: milestone1)
+        end
+
+        context 'complete start and due dates' do
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(milestone1.start_date)
+            expect(subject.due_date).to eq(milestone1.due_date)
+          end
+        end
+
+        context 'without due date' do
+          let(:milestone1) {
+            create(
+              :milestone,
+              start_date: Date.new(2000, 1, 1),
+              due_date: nil
+            )
+          }
+
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(milestone1.start_date)
+            expect(subject.due_date).to eq(nil)
+          end
+        end
+
+        context 'without any dates' do
+          let(:milestone1) {
+            create(
+              :milestone,
+              start_date: nil,
+              due_date: nil
+            )
+          }
+
+          it 'updates to milestone dates' do
+            subject.update_dates
+
+            expect(subject.start_date).to eq(nil)
+            expect(subject.due_date).to eq(nil)
+          end
+        end
       end
     end
   end