Set up has_many relation on Milestone and Release

Updated Release model and its spec file.
Updated Milestone model and its spec file.

app/models/milestone.rb

@@ -30,8 +30,8 @@ class Milestone < ApplicationRecord
   # A one-to-one relationship is set up here as part of a MVC: https://gitlab.com/gitlab-org/gitlab-ce/issues/62402
   # However, on the long term, we will want a many-to-many relationship between Release and Milestone.
   # The "has_one through" allows us today to set up this one-to-one relationship while setting up the architecture for the long-term (ie intermediate table).
-  has_one :milestone_release
-  has_one :release, through: :milestone_release
+  has_many :milestone_releases
+  has_many :releases, through: :milestone_releases
 
   has_internal_id :iid, scope: :project, init: ->(s) { s&.project&.milestones&.maximum(:iid) }
   has_internal_id :iid, scope: :group, init: ->(s) { s&.group&.milestones&.maximum(:iid) }
@@ -68,7 +68,7 @@ class Milestone < ApplicationRecord
   validate :milestone_type_check
   validate :start_date_should_be_less_than_due_date, if: proc { |m| m.start_date.present? && m.due_date.present? }
   validate :dates_within_4_digits
-  validates_associated :milestone_release, message: -> (_, obj) { obj[:value].errors.full_messages.join(",") }
+  validates_associated :milestone_releases, message: -> (_, obj) { obj[:value].map(&:errors).map(&:full_messages).join(",") }
 
   strip_attributes :title
 

app/models/release.rb

@@ -15,8 +15,8 @@ class Release < ApplicationRecord
   # A one-to-one relationship is set up here as part of a MVC: https://gitlab.com/gitlab-org/gitlab-ce/issues/62402
   # However, on the long term, we will want a many-to-many relationship between Release and Milestone.
   # The "has_one through" allows us today to set up this one-to-one relationship while setting up the architecture for the long-term (ie intermediate table).
-  has_one :milestone_release
-  has_one :milestone, through: :milestone_release
+  has_many :milestone_releases
+  has_many :milestones, through: :milestone_releases
 
   default_value_for :released_at, allows_nil: false do
     Time.zone.now
@@ -26,7 +26,7 @@ class Release < ApplicationRecord
 
   validates :description, :project, :tag, presence: true
   validates :name, presence: true, on: :create
-  validates_associated :milestone_release, message: -> (_, obj) { obj[:value].errors.full_messages.join(",") }
+  validates_associated :milestone_releases, message: -> (_, obj) { obj[:value].map(&:errors).map(&:full_messages).join(",") }
 
   scope :sorted, -> { order(released_at: :desc) }
 

spec/models/milestone_spec.rb

@@ -55,20 +55,20 @@ describe Milestone do
       end
     end
 
-    describe 'milestone_release' do
+    describe 'milestone_releases' do
       let(:milestone) { build(:milestone, project: project) }
 
       context 'when it is tied to a release for another project' do
         it 'creates a validation error' do
           other_project = create(:project)
-          milestone.release = build(:release, project: other_project)
+          milestone.releases << build(:release, project: other_project)
           expect(milestone).not_to be_valid
         end
       end
 
       context 'when it is tied to a release for the same project' do
         it 'is valid' do
-          milestone.release = build(:release, project: project)
+          milestone.releases << build(:release, project: project)
           expect(milestone).to be_valid
         end
       end
@@ -78,7 +78,7 @@ describe Milestone do
   describe "Associations" do
     it { is_expected.to belong_to(:project) }
     it { is_expected.to have_many(:issues) }
-    it { is_expected.to have_one(:release) }
+    it { is_expected.to have_many(:releases) }
   end
 
   let(:project) { create(:project, :public) }

spec/models/release_spec.rb

@@ -13,7 +13,7 @@ RSpec.describe Release do
     it { is_expected.to belong_to(:project) }
     it { is_expected.to belong_to(:author).class_name('User') }
     it { is_expected.to have_many(:links).class_name('Releases::Link') }
-    it { is_expected.to have_one(:milestone) }
+    it { is_expected.to have_many(:milestones) }
   end
 
   describe 'validation' do
@@ -38,15 +38,15 @@ RSpec.describe Release do
 
     context 'when a release is tied to a milestone for another project' do
       it 'creates a validation error' do
-        release.milestone = build(:milestone, project: create(:project))
-        expect(release).not_to be_valid
+        milestone = build(:milestone, project: create(:project))
+        expect { release.milestones << milestone }.to raise_error
       end
     end
 
     context 'when a release is tied to a milestone linked to the same project' do
-      it 'is valid' do
-        release.milestone = build(:milestone, project: project)
-        expect(release).to be_valid
+      it 'successfully links this release to this milestone' do
+        milestone = build(:milestone, project: project)
+        expect { release.milestones << milestone }.to change { MilestoneRelease.count }.by(1)
       end
     end
   end