Change DateSourcingMilestonesFinder to be similar to other finderd

Embed DateSourcingMilestoneFinder into migration

ee/app/finders/epics/date_sourcing_milestones_finder.rb

@@ -2,29 +2,31 @@
 
 module Epics
   class DateSourcingMilestonesFinder
+    include Gitlab::Utils::StrongMemoize
+
     FIELDS = [:id, :start_date, :due_date].freeze
     ID_INDEX = FIELDS.index(:id)
     START_DATE_INDEX = FIELDS.index(:start_date)
     DUE_DATE_INDEX = FIELDS.index(:due_date)
 
-    def self.execute(epic_id)
-      results = Milestone.joins(issues: :epic_issue).where(epic_issues: { epic_id: epic_id }).joins(
-        <<~SQL
-          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 = #{epic_id}
-          ) inner_results ON (inner_results.start_date = milestones.start_date OR inner_results.due_date = milestones.due_date)
-        SQL
-      ).pluck(*FIELDS)
-
-      new(results)
+    def initialize(epic_id)
+      @epic_id = epic_id
     end
 
-    def initialize(results)
-      @results = results
+    def execute
+      strong_memoize(:execute) do
+        Milestone.joins(issues: :epic_issue).where(epic_issues: { epic_id: epic_id }).joins(
+          <<~SQL
+            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 = #{epic_id}
+            ) inner_results ON (inner_results.start_date = milestones.start_date OR inner_results.due_date = milestones.due_date)
+          SQL
+        ).pluck(*FIELDS)
+      end
     end
 
     def start_date
@@ -45,16 +47,16 @@ module Epics
 
     private
 
-    attr_reader :results
+    attr_reader :epic_id
 
     def start_date_sourcing_milestone
-      @start_date_sourcing_milestone ||= results
+      @start_date_sourcing_milestone ||= execute
         .reject { |row| row[START_DATE_INDEX].nil? }
         .min_by { |row| row[START_DATE_INDEX] }
     end
 
     def due_date_sourcing_milestone
-      @due_date_sourcing_milestone ||= results
+      @due_date_sourcing_milestone ||= execute
         .reject { |row| row[DUE_DATE_INDEX].nil? }
         .max_by { |row| row[DUE_DATE_INDEX] }
     end

ee/app/models/ee/epic.rb

@@ -93,7 +93,7 @@ module EE
         groups.each do |milestone_ids, epics|
           next if milestone_ids.empty?
 
-          results = Epics::DateSourcingMilestonesFinder.execute(epics.first.id)
+          results = Epics::DateSourcingMilestonesFinder.new(epics.first.id)
 
           self.where(id: epics.map(&:id)).update_all(
             [
@@ -143,7 +143,7 @@ module EE
     alias_attribute(:due_date, :end_date)
 
     def update_start_and_due_dates
-      results = Epics::DateSourcingMilestonesFinder.execute(id)
+      results = Epics::DateSourcingMilestonesFinder.new(id)
 
       self.start_date = start_date_is_fixed? ? start_date_fixed : results.start_date
       self.start_date_sourcing_milestone_id = results.start_date_sourcing_milestone_id

ee/db/post_migrate/20180713171825_update_epic_dates_from_milestones.rb

@@ -25,7 +25,7 @@ class UpdateEpicDatesFromMilestones < ActiveRecord::Migration
       groups.each do |milestone_ids, epics|
         next if milestone_ids.empty?
 
-        data = ::Epics::DateSourcingMilestonesFinder.execute(epics.first.id)
+        data = ::UpdateEpicDatesFromMilestones::Epics::DateSourcingMilestonesFinder.new(epics.first.id)
 
         self.where(id: epics.map(&:id)).update_all(
           [
@@ -45,6 +45,69 @@ class UpdateEpicDatesFromMilestones < ActiveRecord::Migration
     end
   end
 
+  module Epics
+    class DateSourcingMilestonesFinder
+      include Gitlab::Utils::StrongMemoize
+
+      FIELDS = [:id, :start_date, :due_date].freeze
+      ID_INDEX = FIELDS.index(:id)
+      START_DATE_INDEX = FIELDS.index(:start_date)
+      DUE_DATE_INDEX = FIELDS.index(:due_date)
+
+      def initialize(epic_id)
+        @epic_id = epic_id
+      end
+
+      def execute
+        strong_memoize(:execute) do
+          Milestone.joins(issues: :epic_issue).where(epic_issues: { epic_id: epic_id }).joins(
+            <<~SQL
+            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 = #{epic_id}
+            ) inner_results ON (inner_results.start_date = milestones.start_date OR inner_results.due_date = milestones.due_date)
+          SQL
+          ).pluck(*FIELDS)
+        end
+      end
+
+      def start_date
+        start_date_sourcing_milestone&.slice(START_DATE_INDEX)
+      end
+
+      def start_date_sourcing_milestone_id
+        start_date_sourcing_milestone&.slice(ID_INDEX)
+      end
+
+      def due_date
+        due_date_sourcing_milestone&.slice(DUE_DATE_INDEX)
+      end
+
+      def due_date_sourcing_milestone_id
+        due_date_sourcing_milestone&.slice(ID_INDEX)
+      end
+
+      private
+
+      attr_reader :epic_id
+
+      def start_date_sourcing_milestone
+        @start_date_sourcing_milestone ||= execute
+          .reject { |row| row[START_DATE_INDEX].nil? }
+          .min_by { |row| row[START_DATE_INDEX] }
+      end
+
+      def due_date_sourcing_milestone
+        @due_date_sourcing_milestone ||= execute
+          .reject { |row| row[DUE_DATE_INDEX].nil? }
+          .max_by { |row| row[DUE_DATE_INDEX] }
+      end
+    end
+  end
+
   def up
     # Fill fixed date columns for remaining eligible records touched after regular migration is run
     # (20180711014026_update_date_columns_on_epics) but before new app code takes effect.

ee/spec/finders/epics/date_sourcing_milestones_finder_spec.rb

@@ -13,7 +13,7 @@ describe Epics::DateSourcingMilestonesFinder do
       create(:issue, epic: epic, milestone: milestone2)
       create(:issue, epic: epic, milestone: milestone3)
 
-      results = described_class.execute(epic.id)
+      results = described_class.new(epic.id)
 
       expect(results).to have_attributes(
         start_date: milestone1.start_date,
@@ -28,7 +28,7 @@ describe Epics::DateSourcingMilestonesFinder do
       milestone1 = create(:milestone, start_date: Date.new(2000, 1, 1), due_date: Date.new(2000, 1, 10))
       create(:issue, epic: epic, milestone: milestone1)
 
-      results = described_class.execute(epic.id)
+      results = described_class.new(epic.id)
 
       expect(results).to have_attributes(
         start_date: milestone1.start_date,
@@ -43,7 +43,7 @@ describe Epics::DateSourcingMilestonesFinder do
       milestone1 = create(:milestone, start_date: Date.new(2000, 1, 1))
       create(:issue, epic: epic, milestone: milestone1)
 
-      results = described_class.execute(epic.id)
+      results = described_class.new(epic.id)
 
       expect(results).to have_attributes(
         start_date: milestone1.start_date,
@@ -56,7 +56,7 @@ describe Epics::DateSourcingMilestonesFinder do
     it 'handles epics without milestone' do
       epic = create(:epic)
 
-      results = described_class.execute(epic.id)
+      results = described_class.new(epic.id)
 
       expect(results).to have_attributes(
         start_date: nil,