[27746] When validating the contract, ignore the old parent

https://community.openproject.com/wp/27746

app/contracts/work_packages/base_contract.rb

@@ -269,10 +269,19 @@ module WorkPackages
     end
 
     def invalid_relations_with_new_hierarchy
-      Relation
-        .from_parent_to_self_and_descendants(model)
-        .or(Relation.from_self_and_descendants_to_ancestors(model))
-        .direct
+      query = Relation.from_parent_to_self_and_descendants(model)
+                      .or(Relation.from_self_and_descendants_to_ancestors(model))
+                      .direct
+
+      # Ignore the immediate relation from the old parent to the model
+      # since that will still exist before saving.
+      old_parent_id = model.parent_id_was
+
+      if old_parent_id.present?
+        query.where.not(hierarchy: 1, from_id: old_parent_id, to_id: model.id)
+      else
+        query
+      end
     end
   end
 end

spec/services/work_packages/update_service_integration_spec.rb

@@ -1119,4 +1119,27 @@ describe WorkPackages::UpdateService, 'integration tests', type: :model do
       end
     end
   end
+
+  ##
+  # Regression test for #27746
+  # - Parent: A
+  # - Child1: B
+  # - Child2: C
+  #
+  # Trying to set parent of C to B failed because parent relation is requested before change is saved.
+  describe 'Changing parent to a new one that has the same parent as the current element (Regression #27746)' do
+    let(:project) { FactoryGirl.create :project }
+    let!(:wp_a) { FactoryGirl.create :work_package }
+    let!(:wp_b) { FactoryGirl.create :work_package, parent: wp_a }
+    let!(:wp_c) { FactoryGirl.create :work_package, parent: wp_a }
+
+    let(:user) { FactoryGirl.create :admin }
+    let(:work_package) { wp_c }
+
+    let(:attributes) { { parent: wp_b } }
+
+    it 'allows changing the parent' do
+      expect(subject).to be_success
+    end
+  end
 end