simple_form select collection populated by AJAX call

Question

In my view I have a simple form with two select lists:

<%= simple_form_for @job, url: jobs_path do |f| %>
  <%= f.input_field :types, as: :select, collection: @types, id 'types-select' %>
  <%= f.input_field :subtypes, as: :select, collection: @subtypes %>
<% end %>

When a user selects an option from the first list, the second list below should be populated with values from the database based on the above selection.

For this reason, I am making ajax request when a user selects an option from the first list:

$('#types-select').change(function(){
  $.ajax({
    url: '/subtypes',
    dataType: 'json',
    type: 'GET',
    data: {
      type_id: this.value
    },
    success: function(data) {
      console.log(data);
    }
  });
});

Controller looks like this:

class SubtypesController < ApplicationController
  respond_to :json

  def index
    @subtypes = Type.find(params[:type_id]).subtypes
    render json: @subtypes
  end
end

At this point how can I fill up the second select with options from @subtypes?

Answer 1

You can populate second dropdown within success callback. Make sure @subtypes is returned in proper json format too.

Controller:

  def index
    @subtypes = Type.find(params[:type_id]).subtypes
    render json: @subtypes.map { |item| { value: item.value } }  
  end

JS:

  $.ajax({
    url: '/subtypes',
    dataType: 'json',
    type: 'GET',
    data: {
      type_id: this.value
    },
    success: function(data) {
      // Populate second dropdown here
      var output = '';
      $subtypes.empty().append(function() {
        data.forEach(function(item) {
           output += "<option>" + item.value + "</option>"
        });
        return ouput;
      });
    }
  });