Drop preparation for group requirements

Although it would be handy to prepare model also
for group requirements, for MVC these won't be supported
so to avoid any confusion the model supports
only project requirements.

db/migrate/20200226100614_create_requirements.rb

@@ -9,8 +9,7 @@ class CreateRequirements < ActiveRecord::Migration[6.0]
     create_table :requirements do |t|
       t.integer :state, limit: 2, default: 1, null: false
       t.integer :iid, null: false
-      t.references :project, index: true, foreign_key: { on_delete: :cascade }
-      t.references :group, index: true, foreign_key: { to_table: :namespaces, on_delete: :cascade }
+      t.references :project, null: false, index: true, foreign_key: { on_delete: :cascade }
       t.references :author, index: true, foreign_key: { to_table: :users, on_delete: :nullify }
       t.timestamps_with_timezone null: false
       t.string :title, limit: 255, null: false
@@ -21,7 +20,6 @@ class CreateRequirements < ActiveRecord::Migration[6.0]
       t.index :created_at
       t.index :updated_at
       t.index %w(project_id iid), name: 'index_requirements_on_project_id_and_iid', where: 'project_id IS NOT NULL', unique: true, using: :btree
-      t.index %w(group_id iid), name: 'index_requirements_on_group_id_and_iid', where: 'group_id IS NOT NULL', unique: true, using: :btree
     end
   end
 end

db/schema.rb

@@ -3725,8 +3725,7 @@ ActiveRecord::Schema.define(version: 2020_02_27_165129) do
   create_table "requirements", force: :cascade do |t|
     t.integer "state", limit: 2, default: 1, null: false
     t.integer "iid", null: false
-    t.bigint "project_id"
-    t.bigint "group_id"
+    t.bigint "project_id", null: false
     t.bigint "author_id"
     t.datetime_with_timezone "created_at", null: false
     t.datetime_with_timezone "updated_at", null: false
@@ -3734,8 +3733,6 @@ ActiveRecord::Schema.define(version: 2020_02_27_165129) do
     t.text "title_html"
     t.index ["author_id"], name: "index_requirements_on_author_id"
     t.index ["created_at"], name: "index_requirements_on_created_at"
-    t.index ["group_id", "iid"], name: "index_requirements_on_group_id_and_iid", unique: true, where: "(group_id IS NOT NULL)"
-    t.index ["group_id"], name: "index_requirements_on_group_id"
     t.index ["project_id", "iid"], name: "index_requirements_on_project_id_and_iid", unique: true, where: "(project_id IS NOT NULL)"
     t.index ["project_id"], name: "index_requirements_on_project_id"
     t.index ["state"], name: "index_requirements_on_state"
@@ -5017,7 +5014,6 @@ ActiveRecord::Schema.define(version: 2020_02_27_165129) do
   add_foreign_key "releases", "users", column: "author_id", name: "fk_8e4456f90f", on_delete: :nullify
   add_foreign_key "remote_mirrors", "projects", name: "fk_43a9aa4ca8", on_delete: :cascade
   add_foreign_key "repository_languages", "projects", on_delete: :cascade
-  add_foreign_key "requirements", "namespaces", column: "group_id", on_delete: :cascade
   add_foreign_key "requirements", "projects", on_delete: :cascade
   add_foreign_key "requirements", "users", column: "author_id", on_delete: :nullify
   add_foreign_key "resource_label_events", "epics", on_delete: :cascade

ee/app/models/ee/group.rb

@@ -17,7 +17,6 @@ module EE
       add_authentication_token_field :saml_discovery_token, unique: false, token_generator: -> { Devise.friendly_token(8) }
 
       has_many :epics
-      has_many :requirements
 
       has_one :saml_provider
       has_many :ip_restrictions, autosave: true

ee/app/models/requirement.rb

@@ -7,15 +7,9 @@ class Requirement < ApplicationRecord
 
   belongs_to :author, class_name: 'User'
   belongs_to :project
-  belongs_to :group
 
   validates :author, :project, :title, presence: true
 
-  # For MVC, we allow only project-scoped requirements,
-  # but we already know that in the next iteration we will
-  # need also group-scoped requirements
-  validates :group, absence: true
-
   validates :title, length: { maximum: Issuable::TITLE_LENGTH_MAX }
   validates :title_html, length: { maximum: Issuable::TITLE_HTML_LENGTH_MAX }, allow_blank: true
 

ee/spec/models/requirement_spec.rb

@@ -4,14 +4,12 @@ require 'spec_helper'
 
 describe Requirement do
   let_it_be(:user) { create(:user) }
-  let_it_be(:group) { create(:group) }
-  let_it_be(:project) { create(:project, group: group) }
+  let_it_be(:project) { create(:project) }
 
   describe 'associations' do
     subject { build(:requirement) }
 
     it { is_expected.to belong_to(:author).class_name('User') }
-    it { is_expected.to belong_to(:group) }
     it { is_expected.to belong_to(:project) }
   end
 
@@ -21,7 +19,6 @@ describe Requirement do
     it { is_expected.to validate_presence_of(:project) }
     it { is_expected.to validate_presence_of(:author) }
     it { is_expected.to validate_presence_of(:title) }
-    it { is_expected.to validate_absence_of(:group) }
 
     it { is_expected.to validate_length_of(:title).is_at_most(::Issuable::TITLE_LENGTH_MAX) }
     it { is_expected.to validate_length_of(:title_html).is_at_most(::Issuable::TITLE_HTML_LENGTH_MAX) }