Question

Given the following form:

<%= form_for(@ciudad) do |f| %>
  <% if @ciudad.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@ciudad.errors.count, "error") %> prohibited this ciudad from being saved:</h2>

      <ul>
        <% @ciudad.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :nombre %><br />
    <%= f.text_field :nombre %>
  </div>

  <div class="field">
    <%= f.label :departamento_id %><br />
    <%= f.select :departamento_id , :prompt => "Seleccione el municipio" %>
  </div>

  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

How would I populate the options for the deparamento_id select tag from a database?

Answer 1

The simplest way to do that is to use f.collection_select instead of f.select. Assuming you have a table / model named Departamento with a field called nombre:

<%= f.collection_select :departamento_id, Departamento.all, :id, :nombre, :prompt => "Seleccione el municipio" %>

You can read more about it in the official Rails Guides here: http://guides.rubyonrails.org/form_helpers.html#option-tags-from-a-collection-of-arbitrary-objects

And in the API documentation:
http://api.rubyonrails.org/classes/ActionView/Helpers/FormOptionsHelper.html#method-i-collection_select