How to use a checkbox to modify a value from each object of a model using a nested form

I'm new at programming and I have a question related to making a form in Ruby on Rails. I'm making a database for storing products' units. These units are, upon creation, initially located at the storage. This location is stored in a column Unit model. Then I have a model Store and a model Remission.

class Unit < ActiveRecord::Base
  belongs_to :store
  belongs_to :remission
  attr_accessor :into_remission
end

class Remission < ActiveRecord::Base
  belongs_to :store
  has_many :units
  accepts_nested_attributes_for :units
end

class Store < ActiveRecord::Base
  has_many :units
  has_many :remissions
end

Store has_many :remissions and Remission has_many :units. The idea is that when I put some units for selling in a store I have to create a remission. This remission is the list of products that I gave the store so we both can have a reference of which products are at the store. So I have a form to create a remission in which you can select the store that would change the store_id(reference) of the Remission. I also want to select from this same form the units that would take part in this new remission changing the remission_id(reference) from each unit. For that I made a attar_accessor :into_remissions in the Unit model so I could change that to true in each unit that would end up in the remission with a checkbox. I having a lot of problems making this work, here is the code of my form:

<div class="row">
  <div class="col-md-6 col-md-offset-3">
    <%= form_for(@remission) do |f| %>
      <%= render 'shared/error_messages_remissions' %>
#Here you select the store that would own the remission and the products
      <div class="field">
        <%= f.label :store_id, "Producto" %> <br/>
        <%= f.collection_select :store_id, @stores.order(:name), :id, :name, prompt: "Select Store" %>
      </div>
#Here its a dynamic table that display all the products in storage
        <table id="products" class="table table-striped table-bordered" cellspacing="0" width="100%">
          <thead>
            <tr>
              <th>Product Name</th>
              <th>Remission</th>
            </tr>
          </thead>
          <tbody>
      #HERE I WANT TO MAKE A CHECK_BOX THAT CHANGES THE INTO_REMISSION VALUE FROM EACH UNIT. SO IT MARKS THE UNITS THAT WOULD TAKE PART IN THE REMISSION
          <%= f.fields_for :units do |ff| %>
            <% @units.each do |unit| %>
              <% unless unit.sold %>
                <tr>
                  <td><%= unit.product.name %></td>
                  <td>
                      <%= ff.label :into_remission, "Nombre de tu Marca:" %>
                      <%= ff.check_box :into_remission%>
                  </td>
                </tr>
                <% end %>
            <% end %>
          <% end %>
          </tbody>
        </table>
        <%= f.submit "Submit", class: "btn btn-primary" %>
    <% end %>
  </div>
</div>

Needless to say he check_box its now showing nor working. I not sure how to make this work and any advices would be welcome as I'm new with rails and programming. Thanks

Try changing this:

<%= f.fields_for :units do |ff| %>
  <% @units.each do |unit| %>
    <% unless unit.sold %>
      <tr>
        <td><%= unit.product.name %></td>
        <td>
            <%= ff.label :into_remission, "Nombre de tu Marca:" %>
            <%= ff.check_box :into_remission%>
        </td>
      </tr>
      <% end %>
  <% end %>
<% end %>

into this:

<% @units.each do |unit| %>
  <%= f.fields_for :units, unit do |ff| %>
    <% unless unit.sold %>
      <tr>
        <td><%= unit.product.name %></td>
        <td>
            <%= ff.label :into_remission, "Nombre de tu Marca:" %>
            <%= ff.check_box :into_remission%>
        </td>
      </tr>
      <% end %>
  <% end %>
<% end %>

I think you should first iterate over the units and pass each unit separately into the fields for. That should solve the showing issue.