Rule 2: Prevent orphaned children

A parent draft may not be discarded while it has associated child documents whose only edition is linked to that parent draft.

We could offer to drop the draft documents automatically when dropping the parent. But the simpler solution for now is to raise a validation error and force the publisher to drop the child documents manually first.

Author: ChrisBAshton

app/controllers/admin/editions_controller.rb

@@ -197,6 +197,8 @@ def destroy
     else
       redirect_to admin_edition_path(@edition), alert: edition_deleter.failure_reason
     end
+  rescue WhitehallError => e
+    redirect_to admin_edition_path(@edition), alert: e.message
   end
 
   def update_bypass_id

app/models/concerns/standard_edition/parent_document.rb

@@ -1,6 +1,8 @@
 module StandardEdition::ParentDocument
   extend ActiveSupport::Concern
 
+  class UnableToDelete < ::WhitehallError; end
+
   class Trait < Edition::Traits::Trait
     def process_associations_after_save(new_edition)
       ParentChildRelationship
@@ -30,6 +32,8 @@ def process_associations_after_save(new_edition)
              through: :child_relationships,
              source: :child_document
 
+    before_update :ensure_no_new_child_documents!, if: :deleting?
+
     add_trait Trait
   end
 
@@ -48,4 +52,16 @@ def child_editions
   def new_child_documents
     child_documents.where(live_edition_id: nil)
   end
+
+private
+
+  def deleting?
+    will_save_change_to_state? && state == "deleted"
+  end
+
+  def ensure_no_new_child_documents!
+    if allows_child_documents? && new_child_documents.any?
+      raise UnableToDelete, "This document cannot be deleted while it has child documents that have never been published. Delete the draft child documents first."
+    end
+  end
 end

app/models/whitehall_error.rb

@@ -0,0 +1,14 @@
+# Base class for Whitehall-specific domain errors.
+#
+# We rescue WhitehallError in places where we want to handle
+# expected business/application failures gracefully, without also
+# swallowing unexpected framework or programming errors.
+#
+# Avoid rescuing StandardError directly unless we genuinely intend
+# to catch any application exception, including Rails, ActiveRecord,
+# or Ruby runtime errors.
+#
+# Any error inheriting from WhitehallError is considered part of
+# Whitehall's intentional public error surface.
+class WhitehallError < StandardError
+end

features/standard-edition-child-pages.feature

@@ -24,3 +24,12 @@ Feature: Standard Editions - Child Pages
     And I have a published parent configurable document
     Then I should see a "Child documents" section on the document summary page
     And there should be no "Add child document" link
+
+  Scenario: Not able to delete a draft parent if it contains any non-live children
+    Given I am a writer
+    And the configurable document types feature flag is enabled
+    And the test configurable document type group is defined
+    And I have drafted a parent and a child configurable document
+    Then when I click the link "Delete draft"
+    And when I click "Delete"
+    Then I should get the error message "This document cannot be deleted while it has child documents that have never been published. Delete the draft child documents first."

features/step_definitions/standard_edition_child_pages_steps.rb

@@ -74,3 +74,11 @@ def create_parent_standard_edition(state)
 Then(/^there should be no "(.+)" link$/) do |string|
   expect(page).not_to have_link(string)
 end
+
+Given("I have drafted a parent and a child configurable document") do
+  step "I draft a new parent configurable document"
+  step "when I click the link \"Add child document\""
+  step "when I choose a child document type"
+  step "when I fill in and create the child document"
+  visit admin_standard_edition_path(@standard_edition)
+end

test/unit/app/models/concerns/standard_edition/parent_document_test.rb

@@ -227,4 +227,16 @@ class StandardEdition::ParentDocumentTest < ActiveSupport::TestCase
 
     assert_not_includes parent_edition.child_documents, child_edition.document
   end
+
+  test "unable to delete parent edition if it contains any new child documents" do
+    parent_edition = create(:standard_edition)
+
+    parent_edition.stubs(:new_child_documents).returns([create(:standard_edition).document])
+
+    error = assert_raises(StandardEdition::ParentDocument::UnableToDelete) do
+      parent_edition.update!(state: "deleted")
+    end
+
+    assert_equal "This document cannot be deleted while it has child documents that have never been published. Delete the draft child documents first.", error.message
+  end
 end