Prevent projects with same slug from having same project key

Adds service desk setting project_key uniqueness validation.

Changelog: changed

app/models/service_desk_setting.rb

@@ -6,9 +6,12 @@ class ServiceDeskSetting < ApplicationRecord
   belongs_to :project
   validates :project_id, presence: true
   validate :valid_issue_template
+  validate :valid_project_key
   validates :outgoing_name, length: { maximum: 255 }, allow_blank: true
   validates :project_key, length: { maximum: 255 }, allow_blank: true, format: { with: /\A[a-z0-9_]+\z/ }
 
+  scope :with_project_key, ->(key) { where(project_key: key) }
+
   def issue_template_content
     strong_memoize(:issue_template_content) do
       next unless issue_template_key.present?
@@ -27,4 +30,23 @@ class ServiceDeskSetting < ApplicationRecord
       errors.add(:issue_template_key, 'is empty or does not exist')
     end
   end
+
+  def valid_project_key
+    if projects_with_same_slug_and_key_exists?
+      errors.add(:project_key, 'already in use for another service desk address.')
+    end
+  end
+
+  private
+
+  def projects_with_same_slug_and_key_exists?
+    return false unless project_key
+
+    settings = self.class.with_project_key(project_key).preload(:project)
+    project_slug = self.project.full_path_slug
+
+    settings.any? do |setting|
+      setting.project.full_path_slug == project_slug
+    end
+  end
 end

spec/models/service_desk_setting_spec.rb

@@ -31,6 +31,37 @@ RSpec.describe ServiceDeskSetting do
     end
   end
 
+  describe '.valid_project_key' do
+    # Creates two projects with same full path slug
+    # group1/test/one and group1/test-one will both have 'group-test-one' slug
+    let_it_be(:group) { create(:group) }
+    let_it_be(:subgroup) { create(:group, parent: group, name: 'test') }
+    let_it_be(:project1) { create(:project, name: 'test-one', group: group) }
+    let_it_be(:project2) { create(:project, name: 'one', group: subgroup) }
+    let_it_be(:project_key) { 'key' }
+
+    before_all do
+      create(:service_desk_setting, project: project1, project_key: project_key)
+    end
+
+    context 'when project_key is unique for every project slug' do
+      it 'does not add error' do
+        settings = build(:service_desk_setting, project: project2, project_key: 'otherkey')
+
+        expect(settings).to be_valid
+      end
+    end
+
+    context 'when project with same slug and settings project_key exists' do
+      it 'adds error' do
+        settings = build(:service_desk_setting, project: project2, project_key: project_key)
+
+        expect(settings).to be_invalid
+        expect(settings.errors[:project_key].first).to eq('already in use for another service desk address.')
+      end
+    end
+  end
+
   describe 'associations' do
     it { is_expected.to belong_to(:project) }
   end