How to filter records to be edited by nested_form_fields gem in Rails 5.2?

Question

I use the nested_form_fields gem to tranlsate some specific fields in a technical document. Translations are nested fields associated to the document, so that each document has one instance of translation per field per language.

In the _form view to edit the document, nested_form_fields is called for each translated field, and the location to where display the corresponding input is set by the id of the contaning DIV:

<div class="row">
        <div class="col-md-1">
          <%= image_tag("next32.png", :id => "unfold") %>
        </div>
        <div class="col-md-1 text-right"> <%= t('Name')%>:
        </div>
        <div class="col-md-10 field"><%= f.text_field :name, :class => "col-md-8" %>
        </div>
      </div>
      <!-- Translations management -->
      <div class="translation">
        <div class="row">
          <div class="col-md-10 col-md-offset-2" id="name_translation">
            <%= f.nested_fields_for :translations  do |locution| %>
            <div class="row">
              <div class="col-md-1">
                <%= locution.collection_select :language, @other_languages, :property, :name  %>
              </div>
              <div class="col-md-8">
                <%= locution.text_field :description, :class => "col-md-10" %>
              </div>
              <div class="col-md-1">
                <%= locution.remove_nested_fields_link {image_tag("remove.png")} %>
              </div>
              <div class="col-md-1">
                <%= locution.hidden_field :field_name, :value => 'name' %>
              </div>
            </div>
            <% end %>
          </div>
        </div>
        <div class="row">
          <div class="col-md-10 col-md-offset-2">
            <%= f.add_nested_fields_link :translations, image_tag("add.png"), data: {insert_into: "name_translation"} %> <%= t('New') %>
          </div>
        </div>
        <br/>
      </div>
      <!-- End of translations -->

Using this code for 2 or 3 fields in a page, all the translated fields available to the page are displayed in each instance of the nested_fields_for method.

I was wandering if there is a way to add a filter in the f.nested_fields_for :translations (in the form of a block?), or if I have to take all the translation records and filter out in the do |locution| loop.

Thanks for your help!

Answer 1

The solution came from Nico Ritche, the author of the nested_form_fields gem himself:

Filtering does just work like with normal fields_for, you can supply the filtered translations directly:

f.nested_fields_for :translations, your_filtered_translations do |locution|

Which leads to the following update in my code:

<%= f.nested_fields_for :translations, @my_object.translations.where("field_name='name'") do |locution| %>

Thanks a lot Nico!