Make RelativePositioning reusable

RelativePositioning module was heavily dependent on the Issue model.
This changes makes it easier to reuse the functionality provided by
RelativePositioning in other models.

Needed by: https://gitlab.com/gitlab-org/gitlab-ee/issues/12196

app/models/concerns/relative_positioning.rb

 # frozen_string_literal: true
 
+# This module makes it possible to handle items as a list, where the order of items can be easily altered
+# Requirements:
+#
+# - Only works for ActiveRecord models
+# - relative_position integer field must present on the model
+# - This module uses GROUP BY: the model should have a parent relation, example: project -> issues, project is the parent relation (issues table has a parent_id column)
+#
+# Setup like this in the body of your class:
+#
+#     include RelativePositioning
+#
+#     # base query used for the position calculation
+#     def self.relative_positioning_query_base(issue)
+#       where(deleted: false)
+#     end
+#
+#     # column that should be used in GROUP BY
+#     def self.relative_positioning_parent_column
+#       :project_id
+#     end
+#
 module RelativePositioning
   extend ActiveSupport::Concern
 
@@ -93,7 +114,7 @@ module RelativePositioning
     return move_after(before) unless after
     return move_before(after) unless before
 
-    # If there is no place to insert an issue we need to create one by moving the before issue closer
+    # If there is no place to insert an item we need to create one by moving the before item closer
     # to its predecessor. This process will recursively move all the predecessors until we have a place
     if (after.relative_position - before.relative_position) < 2
       before.move_before
@@ -108,11 +129,11 @@ module RelativePositioning
     pos_after = before.next_relative_position
 
     if before.shift_after?
-      issue_to_move = self.class.in_parents(parent_ids).find_by!(relative_position: pos_after)
-      issue_to_move.move_after
-      @positionable_neighbours = [issue_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
+      item_to_move = self.class.relative_positioning_query_base(self).find_by!(relative_position: pos_after)
+      item_to_move.move_after
+      @positionable_neighbours = [item_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
 
-      pos_after = issue_to_move.relative_position
+      pos_after = item_to_move.relative_position
     end
 
     self.relative_position = self.class.position_between(pos_before, pos_after)
@@ -123,11 +144,11 @@ module RelativePositioning
     pos_before = after.prev_relative_position
 
     if after.shift_before?
-      issue_to_move = self.class.in_parents(parent_ids).find_by!(relative_position: pos_before)
-      issue_to_move.move_before
-      @positionable_neighbours = [issue_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
+      item_to_move = self.class.relative_positioning_query_base(self).find_by!(relative_position: pos_before)
+      item_to_move.move_before
+      @positionable_neighbours = [item_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
 
-      pos_before = issue_to_move.relative_position
+      pos_before = item_to_move.relative_position
     end
 
     self.relative_position = self.class.position_between(pos_before, pos_after)
@@ -141,13 +162,13 @@ module RelativePositioning
     self.relative_position = self.class.position_between(min_relative_position || START_POSITION, MIN_POSITION)
   end
 
-  # Indicates if there is an issue that should be shifted to free the place
+  # Indicates if there is an item that should be shifted to free the place
   def shift_after?
     next_pos = next_relative_position
     next_pos && (next_pos - relative_position) == 1
   end
 
-  # Indicates if there is an issue that should be shifted to free the place
+  # Indicates if there is an item that should be shifted to free the place
   def shift_before?
     prev_pos = prev_relative_position
     prev_pos && (relative_position - prev_pos) == 1
@@ -159,7 +180,7 @@ module RelativePositioning
   def save_positionable_neighbours
     return unless @positionable_neighbours
 
-    status = @positionable_neighbours.all? { |issue| issue.save(touch: false) }
+    status = @positionable_neighbours.all? { |item| item.save(touch: false) }
     @positionable_neighbours = nil
 
     status
@@ -170,16 +191,15 @@ module RelativePositioning
     # When calculating across projects, this is much more efficient than
     # MAX(relative_position) without the GROUP BY, due to index usage:
     # https://gitlab.com/gitlab-org/gitlab-ce/issues/54276#note_119340977
-    relation = self.class
-                 .in_parents(parent_ids)
+    relation = self.class.relative_positioning_query_base(self)
                  .order(Gitlab::Database.nulls_last_order('position', 'DESC'))
+                 .group(self.class.relative_positioning_parent_column)
                  .limit(1)
-                 .group(self.class.parent_column)
 
     relation = yield relation if block_given?
 
     relation
-      .pluck(self.class.parent_column, Arel.sql("#{calculation}(relative_position) AS position"))
+      .pluck(self.class.relative_positioning_parent_column, Arel.sql("#{calculation}(relative_position) AS position"))
       .first&.
       last
   end

app/models/issue.rb

@@ -91,11 +91,11 @@ class Issue < ApplicationRecord
     end
   end
 
-  class << self
-    alias_method :in_parents, :in_projects
+  def self.relative_positioning_query_base(issue)
+    in_projects(issue.parent_ids)
   end
 
-  def self.parent_column
+  def self.relative_positioning_parent_column
     :project_id
   end
 

spec/models/concerns/relative_positioning_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-describe RelativePositioning do
-  let(:project) { create(:project) }
-  let(:issue) { create(:issue, project: project) }
-  let(:issue1) { create(:issue, project: project) }
-  let(:new_issue) { create(:issue, project: project) }
-
-  describe '.move_to_end' do
-    it 'moves the object to the end' do
-      Issue.move_to_end([issue, issue1])
-
-      expect(issue1.prev_relative_position).to eq issue.relative_position
-      expect(issue.prev_relative_position).to eq nil
-      expect(issue1.next_relative_position).to eq nil
-    end
-
-    it 'does not perform any moves if all issues have their relative_position set' do
-      issue.update!(relative_position: 1)
-
-      expect(issue).not_to receive(:save)
-
-      Issue.move_to_end([issue])
-    end
-  end
-
-  describe '#max_relative_position' do
-    it 'returns maximum position' do
-      expect(issue.max_relative_position).to eq issue1.relative_position
-    end
-  end
-
-  describe '#prev_relative_position' do
-    it 'returns previous position if there is an issue above' do
-      expect(issue1.prev_relative_position).to eq issue.relative_position
-    end
-
-    it 'returns nil if there is no issue above' do
-      expect(issue.prev_relative_position).to eq nil
-    end
-  end
-
-  describe '#next_relative_position' do
-    it 'returns next position if there is an issue below' do
-      expect(issue.next_relative_position).to eq issue1.relative_position
-    end
-
-    it 'returns nil if there is no issue below' do
-      expect(issue1.next_relative_position).to eq nil
-    end
-  end
-
-  describe '#move_before' do
-    it 'moves issue before' do
-      [issue1, issue].each(&:move_to_end)
-
-      issue.move_before(issue1)
-
-      expect(issue.relative_position).to be < issue1.relative_position
-    end
-  end
-
-  describe '#move_after' do
-    it 'moves issue after' do
-      [issue, issue1].each(&:move_to_end)
-
-      issue.move_after(issue1)
-
-      expect(issue.relative_position).to be > issue1.relative_position
-    end
-  end
-
-  describe '#move_to_end' do
-    before do
-      [issue, issue1].each do |issue|
-        issue.move_to_end && issue.save
-      end
-    end
-
-    it 'moves issue to the end' do
-      new_issue.move_to_end
-
-      expect(new_issue.relative_position).to be > issue1.relative_position
-    end
-  end
-
-  describe '#shift_after?' do
-    before do
-      [issue, issue1].each do |issue|
-        issue.move_to_end && issue.save
-      end
-    end
-
-    it 'returns true' do
-      issue.update(relative_position: issue1.relative_position - 1)
-
-      expect(issue.shift_after?).to be_truthy
-    end
-
-    it 'returns false' do
-      issue.update(relative_position: issue1.relative_position - 2)
-
-      expect(issue.shift_after?).to be_falsey
-    end
-  end
-
-  describe '#shift_before?' do
-    before do
-      [issue, issue1].each do |issue|
-        issue.move_to_end && issue.save
-      end
-    end
-
-    it 'returns true' do
-      issue.update(relative_position: issue1.relative_position + 1)
-
-      expect(issue.shift_before?).to be_truthy
-    end
-
-    it 'returns false' do
-      issue.update(relative_position: issue1.relative_position + 2)
-
-      expect(issue.shift_before?).to be_falsey
-    end
-  end
-
-  describe '#move_between' do
-    before do
-      [issue, issue1].each do |issue|
-        issue.move_to_end && issue.save
-      end
-    end
-
-    it 'positions issue between two other' do
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to be > issue.relative_position
-      expect(new_issue.relative_position).to be < issue1.relative_position
-    end
-
-    it 'positions issue between on top' do
-      new_issue.move_between(nil, issue)
-
-      expect(new_issue.relative_position).to be < issue.relative_position
-    end
-
-    it 'positions issue between to end' do
-      new_issue.move_between(issue1, nil)
-
-      expect(new_issue.relative_position).to be > issue1.relative_position
-    end
-
-    it 'positions issues even when after and before positions are the same' do
-      issue1.update relative_position: issue.relative_position
-
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to be > issue.relative_position
-      expect(issue.relative_position).to be < issue1.relative_position
-    end
-
-    it 'positions issues between other two if distance is 1' do
-      issue1.update relative_position: issue.relative_position + 1
-
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to be > issue.relative_position
-      expect(issue.relative_position).to be < issue1.relative_position
-    end
-
-    it 'positions issue in the middle of other two if distance is big enough' do
-      issue.update relative_position: 6000
-      issue1.update relative_position: 10000
-
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to eq(8000)
-    end
-
-    it 'positions issue closer to the middle if we are at the very top' do
-      issue1.update relative_position: 6000
-
-      new_issue.move_between(nil, issue1)
-
-      expect(new_issue.relative_position).to eq(6000 - RelativePositioning::IDEAL_DISTANCE)
-    end
-
-    it 'positions issue closer to the middle if we are at the very bottom' do
-      issue.update relative_position: 6000
-      issue1.update relative_position: nil
-
-      new_issue.move_between(issue, nil)
-
-      expect(new_issue.relative_position).to eq(6000 + RelativePositioning::IDEAL_DISTANCE)
-    end
-
-    it 'positions issue in the middle of other two if distance is not big enough' do
-      issue.update relative_position: 100
-      issue1.update relative_position: 400
-
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to eq(250)
-    end
-
-    it 'positions issue in the middle of other two is there is no place' do
-      issue.update relative_position: 100
-      issue1.update relative_position: 101
-
-      new_issue.move_between(issue, issue1)
-
-      expect(new_issue.relative_position).to be_between(issue.relative_position, issue1.relative_position)
-    end
-
-    it 'uses rebalancing if there is no place' do
-      issue.update relative_position: 100
-      issue1.update relative_position: 101
-      issue2 = create(:issue, relative_position: 102, project: project)
-      new_issue.update relative_position: 103
-
-      new_issue.move_between(issue1, issue2)
-      new_issue.save!
-
-      expect(new_issue.relative_position).to be_between(issue1.relative_position, issue2.relative_position)
-      expect(issue.reload.relative_position).not_to eq(100)
-    end
-
-    it 'positions issue right if we pass none-sequential parameters' do
-      issue.update relative_position: 99
-      issue1.update relative_position: 101
-      issue2 = create(:issue, relative_position: 102, project: project)
-      new_issue.update relative_position: 103
-
-      new_issue.move_between(issue, issue2)
-      new_issue.save!
-
-      expect(new_issue.relative_position).to be(100)
-    end
-  end
-end

spec/models/issue_spec.rb

@@ -871,4 +871,12 @@ describe Issue do
       expect(issue.labels_hook_attrs).to eq([label.hook_attrs])
     end
   end
+
+  context "relative positioning" do
+    it_behaves_like "a class that supports relative positioning" do
+      let(:project) { create(:project) }
+      let(:factory) { :issue }
+      let(:default_params) { { project: project } }
+    end
+  end
 end

spec/support/shared_examples/relative_positioning_shared_examples.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples "a class that supports relative positioning" do
+  let(:item1) { create(factory, default_params) }
+  let(:item2) { create(factory, default_params) }
+  let(:new_item) { create(factory, default_params) }
+
+  def create_item(params)
+    create(factory, params.merge(default_params))
+  end
+
+  describe '.move_to_end' do
+    it 'moves the object to the end' do
+      item1.update(relative_position: 5)
+      item2.update(relative_position: 15)
+
+      described_class.move_to_end([item1, item2])
+
+      expect(item2.prev_relative_position).to eq item1.relative_position
+      expect(item1.prev_relative_position).to eq nil
+      expect(item2.next_relative_position).to eq nil
+    end
+
+    it 'does not perform any moves if all items have their relative_position set' do
+      item1.update!(relative_position: 1)
+
+      expect(item1).not_to receive(:save)
+
+      described_class.move_to_end([item1])
+    end
+  end
+
+  describe '#max_relative_position' do
+    it 'returns maximum position' do
+      expect(item1.max_relative_position).to eq item2.relative_position
+    end
+  end
+
+  describe '#prev_relative_position' do
+    it 'returns previous position if there is an item above' do
+      item1.update(relative_position: 5)
+      item2.update(relative_position: 15)
+
+      expect(item2.prev_relative_position).to eq item1.relative_position
+    end
+
+    it 'returns nil if there is no item above' do
+      expect(item1.prev_relative_position).to eq nil
+    end
+  end
+
+  describe '#next_relative_position' do
+    it 'returns next position if there is an item below' do
+      item1.update(relative_position: 5)
+      item2.update(relative_position: 15)
+
+      expect(item1.next_relative_position).to eq item2.relative_position
+    end
+
+    it 'returns nil if there is no item below' do
+      expect(item2.next_relative_position).to eq nil
+    end
+  end
+
+  describe '#move_before' do
+    it 'moves item before' do
+      [item2, item1].each(&:move_to_end)
+
+      item1.move_before(item2)
+
+      expect(item1.relative_position).to be < item2.relative_position
+    end
+  end
+
+  describe '#move_after' do
+    it 'moves item after' do
+      [item1, item2].each(&:move_to_end)
+
+      item1.move_after(item2)
+
+      expect(item1.relative_position).to be > item2.relative_position
+    end
+  end
+
+  describe '#move_to_end' do
+    before do
+      [item1, item2].each do |item1|
+        item1.move_to_end && item1.save
+      end
+    end
+
+    it 'moves item to the end' do
+      new_item.move_to_end
+
+      expect(new_item.relative_position).to be > item2.relative_position
+    end
+  end
+
+  describe '#shift_after?' do
+    before do
+      [item1, item2].each do |item1|
+        item1.move_to_end && item1.save
+      end
+    end
+
+    it 'returns true' do
+      item1.update(relative_position: item2.relative_position - 1)
+
+      expect(item1.shift_after?).to be_truthy
+    end
+
+    it 'returns false' do
+      item1.update(relative_position: item2.relative_position - 2)
+
+      expect(item1.shift_after?).to be_falsey
+    end
+  end
+
+  describe '#shift_before?' do
+    before do
+      [item1, item2].each do |item1|
+        item1.move_to_end && item1.save
+      end
+    end
+
+    it 'returns true' do
+      item1.update(relative_position: item2.relative_position + 1)
+
+      expect(item1.shift_before?).to be_truthy
+    end
+
+    it 'returns false' do
+      item1.update(relative_position: item2.relative_position + 2)
+
+      expect(item1.shift_before?).to be_falsey
+    end
+  end
+
+  describe '#move_between' do
+    before do
+      [item1, item2].each do |item1|
+        item1.move_to_end && item1.save
+      end
+    end
+
+    it 'positions item between two other' do
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to be > item1.relative_position
+      expect(new_item.relative_position).to be < item2.relative_position
+    end
+
+    it 'positions item between on top' do
+      new_item.move_between(nil, item1)
+
+      expect(new_item.relative_position).to be < item1.relative_position
+    end
+
+    it 'positions item between to end' do
+      new_item.move_between(item2, nil)
+
+      expect(new_item.relative_position).to be > item2.relative_position
+    end
+
+    it 'positions items even when after and before positions are the same' do
+      item2.update relative_position: item1.relative_position
+
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to be > item1.relative_position
+      expect(item1.relative_position).to be < item2.relative_position
+    end
+
+    it 'positions items between other two if distance is 1' do
+      item2.update relative_position: item1.relative_position + 1
+
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to be > item1.relative_position
+      expect(item1.relative_position).to be < item2.relative_position
+    end
+
+    it 'positions item in the middle of other two if distance is big enough' do
+      item1.update relative_position: 6000
+      item2.update relative_position: 10000
+
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to eq(8000)
+    end
+
+    it 'positions item closer to the middle if we are at the very top' do
+      item2.update relative_position: 6000
+
+      new_item.move_between(nil, item2)
+
+      expect(new_item.relative_position).to eq(6000 - RelativePositioning::IDEAL_DISTANCE)
+    end
+
+    it 'positions item closer to the middle if we are at the very bottom' do
+      new_item.update relative_position: 1
+      item1.update relative_position: 6000
+      item2.destroy
+
+      new_item.move_between(item1, nil)
+
+      expect(new_item.relative_position).to eq(6000 + RelativePositioning::IDEAL_DISTANCE)
+    end
+
+    it 'positions item in the middle of other two if distance is not big enough' do
+      item1.update relative_position: 100
+      item2.update relative_position: 400
+
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to eq(250)
+    end
+
+    it 'positions item in the middle of other two is there is no place' do
+      item1.update relative_position: 100
+      item2.update relative_position: 101
+
+      new_item.move_between(item1, item2)
+
+      expect(new_item.relative_position).to be_between(item1.relative_position, item2.relative_position)
+    end
+
+    it 'uses rebalancing if there is no place' do
+      item1.update relative_position: 100
+      item2.update relative_position: 101
+      item3 = create_item(relative_position: 102)
+      new_item.update relative_position: 103
+
+      new_item.move_between(item2, item3)
+      new_item.save!
+
+      expect(new_item.relative_position).to be_between(item2.relative_position, item3.relative_position)
+      expect(item1.reload.relative_position).not_to eq(100)
+    end
+
+    it 'positions item right if we pass none-sequential parameters' do
+      item1.update relative_position: 99
+      item2.update relative_position: 101
+      item3 = create_item(relative_position: 102)
+      new_item.update relative_position: 103
+
+      new_item.move_between(item1, item3)
+      new_item.save!
+
+      expect(new_item.relative_position).to be(100)
+    end
+  end
+end