Use polymorphism for common attributes in `GroupChildEntity`

app/serializers/group_child_entity.rb

@@ -6,33 +6,25 @@ class GroupChildEntity < Grape::Entity
          :created_at, :updated_at, :avatar_url
 
   expose :type do |instance|
-    instance.class.name.downcase
+    type
   end
 
   expose :can_edit do |instance|
     return false unless request.respond_to?(:current_user)
 
-    if project?
-      can?(request.current_user, :admin_project, instance)
-    else
-      can?(request.current_user, :admin_group, instance)
-    end
+    can?(request.current_user, "admin_#{type}", instance)
   end
 
   expose :edit_path do |instance|
-    if project?
-      edit_project_path(instance)
-    else
-      edit_group_path(instance)
-    end
+    # We know `type` will be one either `project` or `group`.
+    # The `edit_polymorphic_path` helper would try to call the path helper
+    # with a plural: `edit_groups_path(instance)` or `edit_projects_path(instance)`
+    # while our methods are `edit_group_path` or `edit_group_path`
+    public_send("edit_#{type}_path", instance) # rubocop:disable GitlabSecurity/PublicSend
   end
 
   expose :relative_path do |instance|
-    if project?
-      project_path(instance)
-    else
-      group_path(instance)
-    end
+    polymorphic_path(instance)
   end
 
   expose :permission do |instance|
@@ -78,4 +70,8 @@ class GroupChildEntity < Grape::Entity
   def project?
     object.is_a?(Project)
   end
+
+  def type
+    object.class.name.downcase
+  end
 end

spec/serializers/group_child_entity_spec.rb

 require 'spec_helper'
 
 describe GroupChildEntity do
+  include Gitlab::Routing.url_helpers
+
   let(:user) { create(:user) }
   let(:request) { double('request') }
   let(:entity) { described_class.new(object, request: request) }
@@ -24,7 +26,6 @@ describe GroupChildEntity do
        type
        can_edit
        visibility
-       edit_path
        permission
        relative_path].each do |attribute|
       it "includes #{attribute}" do
@@ -51,6 +52,10 @@ describe GroupChildEntity do
       expect(json[:star_count]).to be_present
     end
 
+    it 'has the correct edit path' do
+      expect(json[:edit_path]).to eq(edit_project_path(object))
+    end
+
     it_behaves_like 'group child json'
   end
 
@@ -87,6 +92,10 @@ describe GroupChildEntity do
       expect(json[:can_leave]).to be_truthy
     end
 
+    it 'has the correct edit path' do
+      expect(json[:edit_path]).to eq(edit_group_path(object))
+    end
+
     it_behaves_like 'group child json'
   end
 end