Save parent relationship when editing consent

This follows on from 46c2fa5 which
didn't solve the original problem. In that commit only the check and
confirm page was updated to show the correct parent relationship, but
when we came to actually confirming the consent, the parent relationship
itself still wasn't changing.

This fixes that by replacing the use of `find_or_initialize_by` with a
simple `find` which ensures that the parent relationships remain
attached to the parent and therefore can be saved. I've also updated the
test to ensure this is working as expected and won't regress in the
future.

Jira-Issue: MAV-790

Author: thomasleese

app/models/draft_consent.rb

@@ -174,13 +174,23 @@ def parent
     parent.phone = parent_phone
     parent.phone_receive_updates = parent_phone_receive_updates
 
-    parent
-      .parent_relationships
-      .find_or_initialize_by(patient:)
-      .assign_attributes(
-        type: parent_relationship_type,
-        other_name: parent_relationship_other_name
-      )
+    # We can't use find_or_initialize_by here because we need the object to
+    # remain attached to the parent so we can save the parent with its
+    # relationships.
+
+    parent_relationship =
+      parent.parent_relationships.find { it.patient_id == patient_id } ||
+        parent.parent_relationships.build(patient_id:)
+
+    parent_relationship.assign_attributes(
+      patient:, # acts as preload
+      type: parent_relationship_type,
+      other_name: parent_relationship_other_name
+    )
+
+    if parent_relationship.new_record?
+      parent.parent_relationships << parent_relationship
+    end
 
     parent
   end

spec/features/verbal_consent_change_answers_spec.rb

@@ -18,6 +18,10 @@
       relationship: "Dad"
     )
     then_i_see_the_confirmation_page
+
+    when_i_confirm_the_consent
+    and_i_click_on_the_patient
+    then_i_see_the_new_parent_details
   end
 
   def given_a_patient_is_in_an_hpv_programme
@@ -84,4 +88,17 @@ def then_i_see_the_confirmation_page
   def when_i_click_on_change_name
     click_link "Change name"
   end
+
+  def when_i_confirm_the_consent
+    click_button "Confirm"
+  end
+
+  def and_i_click_on_the_patient
+    click_link @patient.full_name, match: :first
+  end
+
+  def then_i_see_the_new_parent_details
+    expect(page).to have_content("New parent name")
+    expect(page).to have_content("Dad")
+  end
 end