Proper nested records uniqueness validation

Test pass: test_create_duplicate_for_persisted_target_should_fail

app/views/targets/_form.html.erb

@@ -5,6 +5,8 @@
 <% end %>
 
 <%= goal_f.fields_for :targets, @targets, child_index: '' do |target_f| %>
+  <%= error_messages_for target_f.object %>
+
   <p class="target">
   <%= target_f.hidden_field :_destroy %>
   <em class="info"><%= t ".choose_quantity" %></em>

app/views/targets/_new_form.html.erb

@@ -4,7 +4,6 @@
 <%= labelled_form_for @goal, url: goal_targets_path(@goal), method: :post, remote: true,
   html: {id: 'new-target-form', name: 'new-target-form'} do |goal_f| %>
 
-  <%= error_messages_for *@targets %>
   <div class="box tabular">
     <%= render partial: 'targets/form', locals: {goal_f: goal_f} %>
   </div>