fix link_to_add bug when specify target in a 3 level nested form

spec/dummy/app/views/projects/with_target_links.html.erb

@@ -0,0 +1,17 @@
+<%= nested_form_for Project.new do |f| -%>
+  <%= f.text_field :name %>
+  <div id="task-fields">
+    <%= f.fields_for :tasks do |tf| -%>
+      <%= tf.text_field :name %>
+      <div id="milestone-fields">
+        <%= tf.fields_for :milestones do |mf| %>
+          <%= mf.text_field :name %>
+          <%= mf.link_to_remove 'Remove milestone' %>
+        <% end %>
+      </div>
+      <%= tf.link_to_add 'Add new milestone', :milestones, data: {target: '#milestone-fields'} %>
+      <%= tf.link_to_remove 'Remove' %>
+    <% end -%>
+  </div>
+  <%= f.link_to_add 'Add new task', :tasks, data: {target: '#task-fields'} %>
+<% end -%>

spec/form_spec.rb

@@ -40,6 +40,16 @@ def check_form
     inputs.first[:name].should_not eq(inputs.last[:name])
   end
 
+  it 'works when specify target', :js => true do
+    visit '/projects/with_target_links'
+    click_link 'Add new task'
+    click_link 'Remove'
+    click_link 'Add new task'
+    click_link 'Add new milestone'
+
+    page.should have_selector('#milestone-fields .fields', visible: true)
+  end
+
   it 'generates correct name for the nested input', :js => true do
     visit '/projects/new?type=jquery'
     click_link 'Add new task'

vendor/assets/javascripts/jquery_nested_form.js

@@ -60,8 +60,12 @@
     },
     insertFields: function(content, assoc, link) {
       var target = $(link).data('target');
-      if (target) {
-        return $(content).appendTo($(target));
+      if (target) {      
+        if($(link).closest('.fields').length > 0) {
+          return $(content).appendTo($(link).closest('.fields').find($(link).data('target')));          
+        } else {
+          return $(content).appendTo($(target));          
+        }
       } else {
         return $(content).insertBefore(link);
       }