ensl.org/app/views/matches/_lineup.html.erb

<div class="players">
  <% contester.lineup.each do |teamer| %>
    <div class="player fields">
      <% if matcher = @match.matchers.first(conditions: { user_id: teamer.user_id, contester_id: contester.id }) %>
        <%= hidden_field_tag "match[matchers_attributes][#{@n}][id]", matcher.id %>
      <% end %>

      <%= hidden_field_tag "match[matchers_attributes][#{@n}][user_id]", teamer.user_id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][contester_id]", contester.id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][match_id]", @match.id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][merc]", false %>
      <%= check_box_tag "match[matchers_attributes][#{@n}][_destroy]", "keep", !matcher.nil?, { id: "player_#{@n}" } %>

      <%= label_tag "player_#{@n}", '', class: 'checkbox' %>

      <span><%= teamer.user %></span>
    </div>

    <% @n = @n + 1 %>
  <% end %>
</div>

<div class="mercenaries">
  <% @match.matchers.mercs.of_contester(contester).each do |matcher| %>
    <div class="player fields">
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][id]", matcher.id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][user_id]", matcher.user_id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][contester_id]", contester.id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][match_id]", @match.id %>
      <%= hidden_field_tag "match[matchers_attributes][#{@n}][merc]", true %>
      <%= check_box_tag "match[matchers_attributes][#{@n}][_destroy]", "keep", true, { id: "player_#{@n}" } %>

      <%= label_tag "player_#{@n}", '', class: 'checkbox' %>
      
      <span><%= matcher.user %></span>
    </div>

    <% @n = @n + 1 %>
  <% end %>

  <div class="fields">
    <%= hidden_field_tag "match[matchers_attributes][#{@n}][contester_id]", contester.id %>
    <%= hidden_field_tag "match[matchers_attributes][#{@n}][match_id]", @match.id %>
    <%= hidden_field_tag "match[matchers_attributes][#{@n}][merc]", true %>
    <%= hidden_field_tag "match[matchers_attributes][#{@n}][_destroy]", "keep" %>

    <%= text_field_tag "match[matchers_attributes][#{@n}][user_id]", '', placeholder: 'Mercenary' %>

    <% @n = @n + 1 %>
  </div>
</div>