Merge branch 'milestone-issue-sorting-performance' into 'master'

Improve performance of sorting milestone issues

This will fix the problem described in #3066.

See merge request !1609

CHANGELOG

@@ -4,6 +4,7 @@ v 8.2.0 (unreleased)
   - Show last project commit to default branch on project home page
   - Highlight comment based on anchor in URL
   - Adds ability to remove the forked relationship from project settings screen. (Han Loong Liauw)
+  - Improved performance of sorting milestone issues
 
 v 8.1.0 (unreleased)
   - Fix bug preventing mentioned issued from being closed when MR is merged using fast-forward merge.

app/controllers/projects/milestones_controller.rb

@@ -75,11 +75,7 @@ class Projects::MilestonesController < Projects::ApplicationController
   end
 
   def sort_issues
-    @issues = @milestone.issues.where(id: params['sortable_issue'])
-    @issues.each do |issue|
-      issue.position = params['sortable_issue'].index(issue.id.to_s) + 1
-      issue.save
-    end
+    @milestone.sort_issues(params['sortable_issue'].map(&:to_i))
 
     render json: { saved: true }
   end

app/models/milestone.rb

@@ -105,4 +105,36 @@ class Milestone < ActiveRecord::Base
   def author_id
     nil
   end
+
+  # Sorts the issues for the given IDs.
+  #
+  # This method runs a single SQL query using a CASE statement to update the
+  # position of all issues in the current milestone (scoped to the list of IDs).
+  #
+  # Given the ids [10, 20, 30] this method produces a SQL query something like
+  # the following:
+  #
+  #     UPDATE issues
+  #     SET position = CASE
+  #       WHEN id = 10 THEN 1
+  #       WHEN id = 20 THEN 2
+  #       WHEN id = 30 THEN 3
+  #       ELSE position
+  #     END
+  #     WHERE id IN (10, 20, 30);
+  #
+  # This method expects that the IDs given in `ids` are already Fixnums.
+  def sort_issues(ids)
+    pairs = []
+
+    ids.each_with_index do |id, index|
+      pairs << id
+      pairs << index + 1
+    end
+
+    conditions = 'WHEN id = ? THEN ? ' * ids.length
+
+    issues.where(id: ids).
+      update_all(["position = CASE #{conditions} ELSE position END", *pairs])
+  end
 end

spec/benchmarks/models/milestone_spec.rb

+require 'spec_helper'
+
+describe Milestone, benchmark: true do
+  describe '#sort_issues' do
+    let(:milestone) { create(:milestone) }
+
+    let(:issue1) { create(:issue, milestone: milestone) }
+    let(:issue2) { create(:issue, milestone: milestone) }
+    let(:issue3) { create(:issue, milestone: milestone) }
+
+    let(:issue_ids) { [issue3.id, issue2.id, issue1.id] }
+
+    benchmark_subject { milestone.sort_issues(issue_ids) }
+
+    it { is_expected.to iterate_per_second(500) }
+  end
+end

spec/models/milestone_spec.rb

@@ -140,4 +140,32 @@ describe Milestone do
     end
   end
 
+  describe '#sort_issues' do
+    let(:milestone) { create(:milestone) }
+
+    let(:issue1) { create(:issue, milestone: milestone, position: 1) }
+    let(:issue2) { create(:issue, milestone: milestone, position: 2) }
+    let(:issue3) { create(:issue, milestone: milestone, position: 3) }
+    let(:issue4) { create(:issue, position: 42) }
+
+    it 'sorts the given issues' do
+      milestone.sort_issues([issue3.id, issue2.id, issue1.id])
+
+      issue1.reload
+      issue2.reload
+      issue3.reload
+
+      expect(issue1.position).to eq(3)
+      expect(issue2.position).to eq(2)
+      expect(issue3.position).to eq(1)
+    end
+
+    it 'ignores issues not part of the milestone' do
+      milestone.sort_issues([issue3.id, issue2.id, issue1.id, issue4.id])
+
+      issue4.reload
+
+      expect(issue4.position).to eq(42)
+    end
+  end
 end