Added relationships between Release and Milestone

Modified schema via migrations.
Added one-to-one relationship between the two models.
Added changelog file

22 files changed, 385 insertions, 21 deletions

diff --git a/app/models/milestone.rb b/app/models/milestone.rb
index 2ad2838111e..101e963ea29 100644
--- a/app/models/milestone.rb
+++ b/app/models/milestone.rb
@@ -24,6 +24,12 @@ class Milestone < ApplicationRecord
   belongs_to :project
   belongs_to :group
 
+  # 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_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) }
 
@@ -59,6 +65,7 @@ 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(",") }
 
   strip_attributes :title
 
diff --git a/app/models/milestone_release.rb b/app/models/milestone_release.rb
new file mode 100644
index 00000000000..c8743a8cad8
--- /dev/null
+++ b/app/models/milestone_release.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class MilestoneRelease < ApplicationRecord
+  belongs_to :milestone
+  belongs_to :release
+
+  validates :milestone_id, uniqueness: { scope: [:release_id] }
+  validate :same_project_between_milestone_and_release
+
+  private
+
+  def same_project_between_milestone_and_release
+    return if milestone&.project_id == release&.project_id
+
+    errors.add(:base, 'does not have the same project as the milestone')
+  end
+end
diff --git a/app/models/release.rb b/app/models/release.rb
index 459a7c29ad0..b2e65974aa0 100644
--- a/app/models/release.rb
+++ b/app/models/release.rb
@@ -12,6 +12,12 @@ class Release < ApplicationRecord
 
   has_many :links, class_name: 'Releases::Link'
 
+  # 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
+
   default_value_for :released_at, allows_nil: false do
     Time.zone.now
   end
@@ -20,6 +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(",") }
 
   scope :sorted, -> { order(released_at: :desc) }
 
diff --git a/app/services/releases/concerns.rb b/app/services/releases/concerns.rb
index 618d96717b8..b5412e97284 100644
--- a/app/services/releases/concerns.rb
+++ b/app/services/releases/concerns.rb
@@ -47,6 +47,27 @@ module Releases
           project.repository
         end
       end
+
+      def milestone
+        return unless params[:milestone]
+
+        strong_memoize(:milestone) do
+          MilestonesFinder.new(
+            project: project,
+            current_user: current_user,
+            project_ids: Array(project.id),
+            title: params[:milestone]
+          ).execute.first
+        end
+      end
+
+      def inexistent_milestone?
+        params[:milestone] && !params[:milestone].empty? && !milestone
+      end
+
+      def param_for_milestone_title_provided?
+        params[:milestone].present? || params[:milestone]&.empty?
+      end
     end
   end
 end
diff --git a/app/services/releases/create_service.rb b/app/services/releases/create_service.rb
index 5b13ac631ba..c91d43084d3 100644
--- a/app/services/releases/create_service.rb
+++ b/app/services/releases/create_service.rb
@@ -7,6 +7,7 @@ module Releases
     def execute
       return error('Access Denied', 403) unless allowed?
       return error('Release already exists', 409) if release
+      return error('Milestone does not exist', 400) if inexistent_milestone?
 
       tag = ensure_tag
 
@@ -59,7 +60,8 @@ module Releases
         tag: tag.name,
         sha: tag.dereferenced_target.sha,
         released_at: released_at,
-        links_attributes: params.dig(:assets, 'links') || []
+        links_attributes: params.dig(:assets, 'links') || [],
+        milestone: milestone
       )
     end
   end
diff --git a/app/services/releases/update_service.rb b/app/services/releases/update_service.rb
index fabfa398c59..70acc68f747 100644
--- a/app/services/releases/update_service.rb
+++ b/app/services/releases/update_service.rb
@@ -9,6 +9,9 @@ module Releases
       return error('Release does not exist', 404) unless release
       return error('Access Denied', 403) unless allowed?
       return error('params is empty', 400) if empty_params?
+      return error('Milestone does not exist', 400) if inexistent_milestone?
+
+      params[:milestone] = milestone if param_for_milestone_title_provided?
 
       if release.update(params)
         success(tag: existing_tag, release: release)
diff --git a/changelogs/unreleased/62402-milestone-release-be.yml b/changelogs/unreleased/62402-milestone-release-be.yml
new file mode 100644
index 00000000000..3b1f6edfe6b
--- /dev/null
+++ b/changelogs/unreleased/62402-milestone-release-be.yml
@@ -0,0 +1,5 @@
+---
+title: Allow milestones to be associated with a release (backend)
+merge_request: 30816
+author:
+type: added
diff --git a/db/migrate/20190722144316_create_milestone_releases_table.rb b/db/migrate/20190722144316_create_milestone_releases_table.rb
new file mode 100644
index 00000000000..55878bcec41
--- /dev/null
+++ b/db/migrate/20190722144316_create_milestone_releases_table.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class CreateMilestoneReleasesTable < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    create_table :milestone_releases do |t|
+      t.references :milestone, foreign_key: { on_delete: :cascade }, null: false, index: false
+      t.references :release, foreign_key: { on_delete: :cascade }, null: false
+    end
+
+    add_index :milestone_releases, [:milestone_id, :release_id], unique: true, name: 'index_miletone_releases_on_milestone_and_release'
+  end
+
+  def down
+    drop_table :milestone_releases
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 3980627045e..b24558f459e 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -2158,6 +2158,13 @@ ActiveRecord::Schema.define(version: 2019_09_02_131045) do
     t.index ["user_id"], name: "index_merge_trains_on_user_id"
   end
 
+  create_table "milestone_releases", force: :cascade do |t|
+    t.bigint "milestone_id", null: false
+    t.bigint "release_id", null: false
+    t.index ["milestone_id", "release_id"], name: "index_miletone_releases_on_milestone_and_release", unique: true
+    t.index ["release_id"], name: "index_milestone_releases_on_release_id"
+  end
+
   create_table "milestones", id: :serial, force: :cascade do |t|
     t.string "title", null: false
     t.integer "project_id"
@@ -3932,6 +3939,8 @@ ActiveRecord::Schema.define(version: 2019_09_02_131045) do
   add_foreign_key "merge_trains", "merge_requests", on_delete: :cascade
   add_foreign_key "merge_trains", "projects", column: "target_project_id", on_delete: :cascade
   add_foreign_key "merge_trains", "users", on_delete: :cascade
+  add_foreign_key "milestone_releases", "milestones", on_delete: :cascade
+  add_foreign_key "milestone_releases", "releases", on_delete: :cascade
   add_foreign_key "milestones", "namespaces", column: "group_id", name: "fk_95650a40d4", on_delete: :cascade
   add_foreign_key "milestones", "projects", name: "fk_9bd0a0c791", on_delete: :cascade
   add_foreign_key "namespace_aggregation_schedules", "namespaces", on_delete: :cascade
diff --git a/doc/api/releases/index.md b/doc/api/releases/index.md
index 850cf57a06f..8d5b3a65789 100644
--- a/doc/api/releases/index.md
+++ b/doc/api/releases/index.md
@@ -57,6 +57,19 @@ Example response:
          "committer_email":"admin@example.com",
          "committed_date":"2019-01-03T01:55:38.000Z"
       },
+      "milestone":{
+         "id":51,
+         "iid":1,
+         "project_id":24,
+         "title":"v1.0-rc",
+         "description":"Voluptate fugiat possimus quis quod aliquam expedita.",
+         "state":"closed",
+         "created_at":"2019-07-12T19:45:44.256Z",
+         "updated_at":"2019-07-12T19:45:44.256Z",
+         "due_date":"2019-08-16T11:00:00.256Z",
+         "start_date":"2019-07-30T12:00:00.256Z",
+         "web_url":"http://localhost:3000/root/awesome-app/-/milestones/1"
+      },
       "assets":{
          "count":6,
          "sources":[
@@ -205,6 +218,19 @@ Example response:
       "committer_email":"admin@example.com",
       "committed_date":"2019-01-03T01:53:28.000Z"
    },
+   "milestone":{
+      "id":51,
+      "iid":1,
+      "project_id":24,
+      "title":"v1.0-rc",
+      "description":"Voluptate fugiat possimus quis quod aliquam expedita.",
+      "state":"closed",
+      "created_at":"2019-07-12T19:45:44.256Z",
+      "updated_at":"2019-07-12T19:45:44.256Z",
+      "due_date":"2019-08-16T11:00:00.256Z",
+      "start_date":"2019-07-30T12:00:00.256Z",
+      "web_url":"http://localhost:3000/root/awesome-app/-/milestones/1"
+   },
    "assets":{
       "count":4,
       "sources":[
@@ -240,23 +266,24 @@ Create a Release. You need push access to the repository to create a Release.
 POST /projects/:id/releases
 ```
 
-| Attribute          | Type           | Required | Description                                                                                                                      |
-| -------------------| -------------- | -------- | -------------------------------------------------------------------------------------------------------------------------------- |
-| `id`               | integer/string | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding).                                              |
-| `name`             | string         | yes      | The release name.                                                                                                                |
-| `tag_name`         | string         | yes      | The tag where the release will be created from.                                                                                  |
-| `description`      | string         | yes      | The description of the release. You can use [markdown](../../user/markdown.md).                                                  |
-| `ref`              | string         | no       | If `tag_name` doesn't exist, the release will be created from `ref`. It can be a commit SHA, another tag name, or a branch name. |
-| `assets:links`     | array of hash  | no       | An array of assets links.                                                                                                        |
-| `assets:links:name`| string         | required by: `assets:links` | The name of the link.                                                                                         |
-| `assets:links:url` | string         | required by: `assets:links` | The url of the link.                                                                                          |
-| `released_at`      | datetime       | no       | The date when the release will be/was ready. Defaults to the current time. Expected in ISO 8601 format (`2019-03-15T08:00:00Z`). |
+| Attribute          | Type            | Required | Description                                                                                                                      |
+| -------------------| --------------- | -------- | -------------------------------------------------------------------------------------------------------------------------------- |
+| `id`               | integer/string  | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding).                                              |
+| `name`             | string          | yes      | The release name.                                                                                                                |
+| `tag_name`         | string          | yes      | The tag where the release will be created from.                                                                                  |
+| `description`      | string          | yes      | The description of the release. You can use [markdown](../../user/markdown.md).                                                  |
+| `ref`              | string          | no       | If `tag_name` doesn't exist, the release will be created from `ref`. It can be a commit SHA, another tag name, or a branch name. |
+| `milestone`        | string          | no       | The title of the milestone the release is associated with.                                                                       |
+| `assets:links`     | array of hash   | no       | An array of assets links.                                                                                                        |
+| `assets:links:name`| string          | required by: `assets:links` | The name of the link.                                                                                         |
+| `assets:links:url` | string          | required by: `assets:links` | The url of the link.                                                                                          |
+| `released_at`      | datetime        | no       | The date when the release will be/was ready. Defaults to the current time. Expected in ISO 8601 format (`2019-03-15T08:00:00Z`). |
 
 Example request:
 
 ```sh
 curl --header 'Content-Type: application/json' --header "PRIVATE-TOKEN: gDybLx3yrUK_HLp3qPjS" \
-     --data '{ "name": "New release", "tag_name": "v0.3", "description": "Super nice release", "assets": { "links": [{ "name": "hoge", "url": "https://google.com" }] } }' \
+     --data '{ "name": "New release", "tag_name": "v0.3", "description": "Super nice release", "milestone": "v1.0-rc", "assets": { "links": [{ "name": "hoge", "url": "https://google.com" }] } }' \
      --request POST https://gitlab.example.com/api/v4/projects/24/releases
 ```
 
@@ -294,6 +321,19 @@ Example response:
       "committer_email":"admin@example.com",
       "committed_date":"2019-01-03T01:55:38.000Z"
    },
+   "milestone":{
+      "id":51,
+      "iid":1,
+      "project_id":24,
+      "title":"v1.0-rc",
+      "description":"Voluptate fugiat possimus quis quod aliquam expedita.",
+      "state":"active",
+      "created_at":"2019-07-12T19:45:44.256Z",
+      "updated_at":"2019-07-12T19:45:44.256Z",
+      "due_date":"2019-08-16T11:00:00.256Z",
+      "start_date":"2019-07-30T12:00:00.256Z",
+      "web_url":"http://localhost:3000/root/awesome-app/-/milestones/1"
+   },
    "assets":{
       "count":5,
       "sources":[
@@ -334,18 +374,19 @@ Update a Release.
 PUT /projects/:id/releases/:tag_name
 ```
 
-| Attribute     | Type           | Required | Description                                                                                        |
-| ------------- | -------------- | -------- | -------------------------------------------------------------------------------------------------- |
-| `id`          | integer/string | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding).                |
-| `tag_name`    | string         | yes      | The tag where the release will be created from.                                                    |
-| `name`        | string         | no       | The release name.                                                                                  |
-| `description` | string         | no       | The description of the release. You can use [markdown](../../user/markdown.md).                    |
-| `released_at` | datetime       | no       | The date when the release will be/was ready. Expected in ISO 8601 format (`2019-03-15T08:00:00Z`). |
+| Attribute     | Type           | Required | Description                                                                                               |
+| ------------- | -------------- | -------- | --------------------------------------------------------------------------------------------------------- |
+| `id`          | integer/string | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding).                       |
+| `tag_name`    | string         | yes      | The tag where the release will be created from.                                                           |
+| `name`        | string         | no       | The release name.                                                                                         |
+| `description` | string         | no       | The description of the release. You can use [markdown](../../user/markdown.md).                           |
+| `milestone`   | string         | no       | The title of the milestone to associate with the release (`""` to remove the milestone from the release). |
+| `released_at` | datetime       | no       | The date when the release will be/was ready. Expected in ISO 8601 format (`2019-03-15T08:00:00Z`).        |
 
 Example request:
 
 ```sh
-curl --request PUT --data name="new name" --header "PRIVATE-TOKEN: gDybLx3yrUK_HLp3qPjS" "https://gitlab.example.com/api/v4/projects/24/releases/v0.1"
+curl --header 'Content-Type: application/json' --request PUT --data '{"name": "new name", "milestone": "v1.0"}' --header "PRIVATE-TOKEN: gDybLx3yrUK_HLp3qPjS" "https://gitlab.example.com/api/v4/projects/24/releases/v0.1"
 ```
 
 Example response:
@@ -382,6 +423,19 @@ Example response:
       "committer_email":"admin@example.com",
       "committed_date":"2019-01-03T01:53:28.000Z"
    },
+   "milestone":{
+      "id":53,
+      "iid":2,
+      "project_id":24,
+      "title":"v1.0",
+      "description":"Voluptate fugiat possimus quis quod aliquam expedita.",
+      "state":"active",
+      "created_at":"2019-09-01T13:00:00.256Z",
+      "updated_at":"2019-09-01T13:00:00.256Z",
+      "due_date":"2019-09-20T13:00:00.256Z",
+      "start_date":"2019-09-05T12:00:00.256Z",
+      "web_url":"http://localhost:3000/root/awesome-app/-/milestones/3"
+   },
    "assets":{
       "count":4,
       "sources":[
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index cfcf6228225..ba58e125568 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -1229,6 +1229,7 @@ module API
       expose :author, using: Entities::UserBasic, if: -> (release, _) { release.author.present? }
       expose :commit, using: Entities::Commit, if: lambda { |_, _| can_download_code? }
       expose :upcoming_release?, as: :upcoming_release
+      expose :milestone, using: Entities::Milestone, if: -> (release, _) { release.milestone.present? }
 
       expose :assets do
         expose :assets_count, as: :count do |release, _|
diff --git a/lib/api/releases.rb b/lib/api/releases.rb
index 7a3d804c30c..11a9a085068 100644
--- a/lib/api/releases.rb
+++ b/lib/api/releases.rb
@@ -54,6 +54,7 @@ module API
             requires :url, type: String
           end
         end
+        optional :milestone, type: String, desc: 'The title of the related milestone'
         optional :released_at, type: DateTime, desc: 'The date when the release will be/was ready. Defaults to the current time.'
       end
       post ':id/releases' do
@@ -79,6 +80,7 @@ module API
         optional :name,        type: String, desc: 'The name of the release'
         optional :description, type: String, desc: 'Release notes with markdown support'
         optional :released_at, type: DateTime, desc: 'The date when the release will be/was ready.'
+        optional :milestone,   type: String, desc: 'The title of the related milestone'
       end
       put ':id/releases/:tag_name', requirements: RELEASE_ENDPOINT_REQUIREMETS do
         authorize_update_release!
diff --git a/spec/factories/milestone_releases.rb b/spec/factories/milestone_releases.rb
new file mode 100644
index 00000000000..08e109480ab
--- /dev/null
+++ b/spec/factories/milestone_releases.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :milestone_release do
+    milestone
+    release
+
+    before(:create, :build) do |mr|
+      project = create(:project)
+      mr.milestone.project = project
+      mr.release.project = project
+    end
+  end
+end
diff --git a/spec/fixtures/api/schemas/public_api/v4/release.json b/spec/fixtures/api/schemas/public_api/v4/release.json
index ec3fa59cdb1..078b1c0b982 100644
--- a/spec/fixtures/api/schemas/public_api/v4/release.json
+++ b/spec/fixtures/api/schemas/public_api/v4/release.json
@@ -15,6 +15,7 @@
     "author": {
       "oneOf": [{ "type": "null" }, { "$ref": "user/basic.json" }]
     },
+    "milestone": { "type": "string" },
     "assets": {
       "required": ["count", "links", "sources"],
       "properties": {
diff --git a/spec/lib/gitlab/import_export/all_models.yml b/spec/lib/gitlab/import_export/all_models.yml
index ec4a6ef05b9..c6aa4a2482c 100644
--- a/spec/lib/gitlab/import_export/all_models.yml
+++ b/spec/lib/gitlab/import_export/all_models.yml
@@ -62,6 +62,8 @@ milestone:
 - participants
 - events
 - boards
+- milestone_release
+- release
 snippets:
 - author
 - project
@@ -72,6 +74,8 @@ releases:
 - author
 - project
 - links
+- milestone_release
+- milestone
 links:
 - release
 project_members:
@@ -484,3 +488,6 @@ lists:
 - board
 - label
 - list_user_preferences
+milestone_releases:
+- milestone
+- release
diff --git a/spec/models/milestone_release_spec.rb b/spec/models/milestone_release_spec.rb
new file mode 100644
index 00000000000..d6f73275977
--- /dev/null
+++ b/spec/models/milestone_release_spec.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MilestoneRelease do
+  let(:project) { create(:project) }
+  let(:release) { create(:release, project: project) }
+  let(:milestone) { create(:milestone, project: project) }
+
+  subject { build(:milestone_release, release: release, milestone: milestone) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:milestone) }
+    it { is_expected.to belong_to(:release) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to validate_uniqueness_of(:milestone_id).scoped_to(:release_id) }
+
+    context 'when milestone and release do not have the same project' do
+      it 'is not valid' do
+        other_project = create(:project)
+        release = build(:release, project: other_project)
+        milestone_release = described_class.new(milestone: milestone, release: release)
+        expect(milestone_release).not_to be_valid
+      end
+    end
+
+    context 'when milestone and release have the same project' do
+      it 'is valid' do
+        milestone_release = described_class.new(milestone: milestone, release: release)
+        expect(milestone_release).to be_valid
+      end
+    end
+  end
+end
diff --git a/spec/models/milestone_spec.rb b/spec/models/milestone_spec.rb
index 3704a2d468d..64030f5b92a 100644
--- a/spec/models/milestone_spec.rb
+++ b/spec/models/milestone_spec.rb
@@ -54,11 +54,31 @@ describe Milestone do
         expect(milestone.errors[:due_date]).to include("date must not be after 9999-12-31")
       end
     end
+
+    describe 'milestone_release' 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)
+          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)
+          expect(milestone).to be_valid
+        end
+      end
+    end
   end
 
   describe "Associations" do
     it { is_expected.to belong_to(:project) }
     it { is_expected.to have_many(:issues) }
+    it { is_expected.to have_one(:release) }
   end
 
   let(:project) { create(:project, :public) }
diff --git a/spec/models/release_spec.rb b/spec/models/release_spec.rb
index e9d846e7291..29ce9f762b0 100644
--- a/spec/models/release_spec.rb
+++ b/spec/models/release_spec.rb
@@ -13,6 +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) }
   end
 
   describe 'validation' do
@@ -34,6 +35,20 @@ RSpec.describe Release do
         expect(existing_release_without_name.name).to be_nil
       end
     end
+
+    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
+      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
+      end
+    end
   end
 
   describe '#assets_count' do
diff --git a/spec/services/milestones/destroy_service_spec.rb b/spec/services/milestones/destroy_service_spec.rb
index 3a22e4d4f92..ff1e1256166 100644
--- a/spec/services/milestones/destroy_service_spec.rb
+++ b/spec/services/milestones/destroy_service_spec.rb
@@ -65,5 +65,19 @@ describe Milestones::DestroyService do
         expect { service.execute(group_milestone) }.not_to change { Event.count }
       end
     end
+
+    context 'when a release is tied to a milestone' do
+      it 'destroys the milestone but not the associated release' do
+        release = create(
+          :release,
+          tag: 'v1.0',
+          project: project,
+          milestone: milestone
+        )
+
+        expect { service.execute(milestone) }.not_to change { Release.count }
+        expect(release.reload).to be_persisted
+      end
+    end
   end
 end
diff --git a/spec/services/releases/create_service_spec.rb b/spec/services/releases/create_service_spec.rb
index e26676cdd55..5c9d6537df1 100644
--- a/spec/services/releases/create_service_spec.rb
+++ b/spec/services/releases/create_service_spec.rb
@@ -72,6 +72,15 @@ describe Releases::CreateService do
         expect(project.releases.find_by(tag: tag_name).description).to eq(description)
       end
     end
+
+    context 'when a passed-in milestone does not exist for this project' do
+      it 'raises an error saying the milestone is inexistent' do
+        service = described_class.new(project, user, params.merge!({ milestone: 'v111.0' }))
+        result = service.execute
+        expect(result[:status]).to eq(:error)
+        expect(result[:message]).to eq('Milestone does not exist')
+      end
+    end
   end
 
   describe '#find_or_build_release' do
@@ -80,5 +89,58 @@ describe Releases::CreateService do
 
       expect(project.releases.count).to eq(0)
     end
+
+    context 'when existing milestone is passed in' do
+      let(:title) { 'v1.0' }
+      let(:milestone) { create(:milestone, :active, project: project, title: title) }
+      let(:params_with_milestone) { params.merge!({ milestone: title }) }
+
+      it 'creates a release and ties this milestone to it' do
+        service = described_class.new(milestone.project, user, params_with_milestone)
+        result = service.execute
+
+        expect(project.releases.count).to eq(1)
+        expect(result[:status]).to eq(:success)
+
+        release = project.releases.last
+
+        expect(release.milestone).to eq(milestone)
+      end
+
+      context 'when another release was previously created with that same milestone linked' do
+        it 'also creates another release tied to that same milestone' do
+          other_release = create(:release, milestone: milestone, project: project, tag: 'v1.0')
+          service = described_class.new(milestone.project, user, params_with_milestone)
+          service.execute
+          release = project.releases.last
+
+          expect(release.milestone).to eq(milestone)
+          expect(other_release.milestone).to eq(milestone)
+          expect(release.id).not_to eq(other_release.id)
+        end
+      end
+    end
+
+    context 'when no milestone is passed in' do
+      it 'creates a release without a milestone tied to it' do
+        expect(params.key? :milestone).to be_falsey
+        service.execute
+        release = project.releases.last
+        expect(release.milestone).to be_nil
+      end
+
+      it 'does not create any new MilestoneRelease object' do
+        expect { service.execute }.not_to change { MilestoneRelease.count }
+      end
+    end
+
+    context 'when an empty value is passed as a milestone' do
+      it 'creates a release without a milestone tied to it' do
+        service = described_class.new(project, user, params.merge!({ milestone: '' }))
+        service.execute
+        release = project.releases.last
+        expect(release.milestone).to be_nil
+      end
+    end
   end
 end
diff --git a/spec/services/releases/destroy_service_spec.rb b/spec/services/releases/destroy_service_spec.rb
index f4c901e6585..c3172e5edbc 100644
--- a/spec/services/releases/destroy_service_spec.rb
+++ b/spec/services/releases/destroy_service_spec.rb
@@ -57,5 +57,15 @@ describe Releases::DestroyService do
                                http_status: 403)
       end
     end
+
+    context 'when a milestone is tied to the release' do
+      let!(:milestone) { create(:milestone, :active, project: project, title: 'v1.0') }
+      let!(:release) { create(:release, milestone: milestone, project: project, tag: tag) }
+
+      it 'destroys the release but leave the milestone intact' do
+        expect { subject }.not_to change { Milestone.count }
+        expect(milestone.reload).to be_persisted
+      end
+    end
   end
 end
diff --git a/spec/services/releases/update_service_spec.rb b/spec/services/releases/update_service_spec.rb
index 14e6a5f13c8..944f3d8c9ad 100644
--- a/spec/services/releases/update_service_spec.rb
+++ b/spec/services/releases/update_service_spec.rb
@@ -48,5 +48,42 @@ describe Releases::UpdateService do
 
       it_behaves_like 'a failed update'
     end
+
+    context 'when a milestone is passed in' do
+      let(:old_title) { 'v1.0' }
+      let(:new_title) { 'v2.0' }
+      let(:milestone) { create(:milestone, project: project, title: old_title) }
+      let(:new_milestone) { create(:milestone, project: project, title: new_title) }
+      let(:params_with_milestone) { params.merge!({ milestone: new_title }) }
+
+      before do
+        release.milestone = milestone
+        release.save!
+
+        described_class.new(new_milestone.project, user, params_with_milestone).execute
+        release.reload
+      end
+
+      it 'updates the related milestone accordingly' do
+        expect(release.milestone.title).to eq(new_title)
+      end
+    end
+
+    context "when an 'empty' milestone is passed in" do
+      let(:milestone) { create(:milestone, project: project, title: 'v1.0') }
+      let(:params_with_empty_milestone) { params.merge!({ milestone: '' }) }
+
+      before do
+        release.milestone = milestone
+        release.save!
+
+        described_class.new(milestone.project, user, params_with_empty_milestone).execute
+        release.reload
+      end
+
+      it 'removes the old milestone and does not associate any new milestone' do
+        expect(release.milestone).to be_nil
+      end
+    end
   end
 end