Add create and delete relation links to representers.

lib/api/v3/work_packages/relation_representer.rb

@@ -62,6 +62,14 @@ module API
           { href: "#{root_url}api/v3/work_packages/#{represented.model.to_id}" }
         end
 
+        link :remove do
+          {
+            href: "#{root_url}api/v3/relationships/#{represented.model.id}",
+            method: :delete,
+            title: "Remove relation"
+          } if current_user_allowed_to(:manage_work_package_relations)
+        end
+
         property :delay, getter: -> (*) { model.delay }, render_nil: true, if: -> (*) { model.relation_type == 'precedes' }
 
         def _type
@@ -70,6 +78,10 @@ module API
 
         private
 
+        def current_user_allowed_to(permission)
+          @current_user && @current_user.allowed_to?(permission, represented.model.from.project)
+        end
+
         def relation_type
           relation = represented.model
           relation.relation_type_for(relation.to).camelize

lib/api/v3/work_packages/work_package_representer.rb

@@ -109,6 +109,14 @@ module API
           } if current_user_allowed_to(:add_work_package_watchers, represented.work_package)
         end
 
+        link :addRelation do
+          {
+              href: "#{root_url}/api/v3/work_packages/#{represented.work_package.id}/relations",
+              method: :post,
+              title: 'Add relation'
+          } if current_user_allowed_to(:manage_work_package_relations, represented.work_package)
+        end
+
         link :parent do
           {
               href: "#{root_url}/api/v3/work_packages/#{represented.work_package.parent.id}",
@@ -160,7 +168,7 @@ module API
         end
 
         def relations
-          represented.relations.map{ |relation| RelationRepresenter.new(relation, work_package: represented.work_package) }
+          represented.relations.map{ |relation| RelationRepresenter.new(relation, work_package: represented.work_package, current_user: @current_user) }
         end
 
         def custom_properties

spec/lib/api/v3/work_packages/work_package_representer_spec.rb

@@ -44,7 +44,7 @@ describe ::API::V3::WorkPackages::WorkPackageRepresenter do
     )
   }
   let(:project) { work_package.project }
-  let(:permissions) { %i(view_work_packages view_work_package_watchers add_work_package_watchers delete_work_package_watchers) }
+  let(:permissions) { %i(view_work_packages view_work_package_watchers add_work_package_watchers delete_work_package_watchers manage_work_package_relations) }
   let(:role) { FactoryGirl.create :role, permissions: permissions }
 
   before(:each) do
@@ -150,6 +150,22 @@ describe ::API::V3::WorkPackages::WorkPackageRepresenter do
           expect(subject).to_not have_json_path('_links/add_watcher/href')
         end
       end
+
+      context 'when the user has the permission to manage relations' do
+        it 'should have a link to add relation' do
+          expect(subject).to have_json_path('_links/addRelation/href')
+        end
+      end
+
+      context 'when the user does not have the permission to manage relations' do
+        before do
+          role.permissions.delete(:manage_work_package_relations) and role.save
+        end
+
+        it 'should not have a link to add relation' do
+          expect(subject).to_not have_json_path('_links/addRelation/href')
+        end
+      end
     end
 
     describe '_embedded' do