Auto-Complete Association in Rails 5


Step 1

Generate a new Rails 5 project and products controller.

rails new auto
rails g controller products

Step 2

The products controller looks like this:

class ProductsController < ApplicationController
  def index
    @products = Product.all

  def show
    @product = Product.find(params[:id])

  def new
    @product =

  def create
    @product =
      redirect_to products_url, notice: "Successfully created product."
      render :new

  def edit
    @product = Product.find(params[:id])

  def update
    @product = Product.find(params[:id])
    if @product.update_attributes(allowed_params)
      redirect_to products_url, notice: "Successfully created product."
      render :edit

  def destroy
    @product = Product.find(params[:id])
    redirect_to products_url, notice: "Successfully destroyed product."

  def allowed_params

Step 3

Generate the category model and product model.

rails g model category name
rails g model product name price:decimal category_id:integer
rails g model product name price:decimal category:references

You can see Rails 5 added a foreign key for category_id.

class CreateProducts < ActiveRecord::Migration[5.0]
  def change
    create_table :products do |t|
      t.string :name
      t.decimal :price
      t.references :category, foreign_key: true


Run the migration.

rails db:migrate

You can see the generated tables in schema.rb. It shows the index for the category_id foreign key.

ActiveRecord::Schema.define(version: 20160408204755) do
  create_table "categories", force: :cascade do |t|
    t.string   "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false

  create_table "products", force: :cascade do |t|
    t.string   "name"
    t.decimal  "price"
    t.integer  "category_id"
    t.datetime "created_at",  null: false
    t.datetime "updated_at",  null: false

  add_index "products", ["category_id"], name: "index_products_on_category_id"

Step 4

Let's add some records to play with in the seeds.rb:

Category.create!(name: "Beverages")
Category.create!(name: "Books")
Category.create!(name: "Breads")
Category.create!(name: "Canned Foods")
Category.create!(name: "Clothes")
Category.create!(name: "Computers")
Category.create!(name: "Dry Foods")
Category.create!(name: "Frozen Foods")
Category.create!(name: "Furniture")
Category.create!(name: "Headphones")
Category.create!(name: "Magazines")
Category.create!(name: "Music")
Category.create!(name: "Other Electronics")
Category.create!(name: "Pastas")
Category.create!(name: "Portable Devices")
Category.create!(name: "Produce")
Category.create!(name: "Snacks")
Category.create!(name: "Software")
Category.create!(name: "Televisions")
Category.create!(name: "Toys")
Category.create!(name: "Video Games")
Category.create!(name: "Video Players")
Category.create!(name: "Videos")

Product.create!(name: "Tasty Baklava", price: 3.99, category: Category.find_by(name: "Dry Foods"))
Product.create!(name: "Flux Capacitor", price: 19.55, category: Category.find_by(name: "Other Electronics"))
Product.create!(name: "Technodrome", price: 12.49, category: Category.find_by(name: "Toys"))
Product.create!(name: "TextMate 2", price: 74.99, category: Category.find_by(name: "Software"))

Populate the database:

rails db:seed

Step 5

Here is the new.html.erb:

<h1>New Product</h1>

<%= render 'form' %>

Here is the _form.html.erb:

<%= form_for(@product) do |f| %>
  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  <div class="field">
    <%= f.label :price %><br />
    <%= f.text_field :price %>
  <div class="field">
    <%= f.label :category_id %><br />
    <%= f.collection_select :category_id, Category.order(:name), :id, :name, include_blank: true %>
  <div class="actions">
    <%= f.submit %>
<% end %>

Step 6

In app/assets/stylesheets/application.css, add the following css:

 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
 * or any plugin's vendor/assets/stylesheets directory can be referenced here using a relative path.
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *= require_tree .
 *= require_self

body {
  background-color: #4B7399;
  font-family: Verdana, Helvetica, Arial;
  font-size: 14px;

a img {
  border: none;

a {
  color: #0000FF;

.clear {
  clear: both;
  height: 0;
  overflow: hidden;

#container {
  width: 75%;
  margin: 0 auto;
  background-color: #FFF;
  padding: 20px 40px;
  border: solid 1px black;
  margin-top: 20px;

#flash_notice, #flash_error, #flash_alert {
  padding: 5px 8px;
  margin: 10px 0;

#flash_notice {
  background-color: #CFC;
  border: solid 1px #6C6;

#flash_error, #flash_alert {
  background-color: #FCC;
  border: solid 1px #C66;

.fieldWithErrors {
  display: inline;

.error_messages {
  width: 400px;
  border: 2px solid #CF0000;
  padding: 0px;
  padding-bottom: 12px;
  margin-bottom: 20px;
  background-color: #f0f0f0;
  font-size: 12px;

.error_messages h2 {
  text-align: left;
  font-weight: bold;
  padding: 5px 10px;
  font-size: 12px;
  margin: 0;
  background-color: #c00;
  color: #fff;

.error_messages p {
  margin: 8px 10px;

.error_messages ul {
  margin: 0;

form .field, form .actions {
  margin: 12px 0;

.product h2 {
  font-size: 16px;
  margin-bottom: 2px;

Step 7

The index.html.erb looks like this:

<div id="products">
<% @products.each do |product| %>
  <div class="product">
    <h2><%= link_to, product %></h2>
    <div class="details">
      <%= number_to_currency(product.price) %>
      <% if product.category %>
        | Category: <%= %>
      <% end %>
      | <%= link_to "Edit", edit_product_path(product) %>
<% end %>

<p><%= link_to "New Product", new_product_path %></p>

The application layout file looks like this:

<!DOCTYPE html>
    <%= csrf_meta_tags %>
    <%= action_cable_meta_tag %>

    <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => 'reload' %>
    <%= javascript_include_tag 'application', 'data-turbolinks-track' => 'reload' %>
    <div id="container">
      <% flash.each do |name, msg| %>
        <%= content_tag :div, msg, :id => "flash_#{name}" %>
      <% end %>
      <%= yield %>

You can now see the list of products.

Step 8

Here is the show.html.erb

  <%= %>
  <%= @product.price %>
  <%= @product.category && %>
<%= link_to 'Edit', edit_product_path(@product) %> |
<%= link_to 'Back', products_path %>

Here is the edit.html.erb.

<h1>Editing product</h1>
<%= render 'form' %>

Step 9

Change the dropdown to a text field in product form partial:

<%= f.collection_select :category_id, Category.order(:name), :id, :name, include_blank: true %>


<%= f.text_field :category_name %>

Step 10

Reload the new product page. You will get the error:

undefined method `category_name' for #<Product:0x007fbd8f81b588>
Did you mean?  category

Step 11


def category_name

def category_name=(name)
  self.category = Category.find_by(name: name) if name.present?

to product model.

Step 12

Reload the new product page. Create a new product by filling out the product name, price and the category in the text field. You will see the product is created.

Step 13

Let's allow user to create a new category if the category does not exist when they create a new product. Change the category_name setter:

def category_name=(name)
  self.category = Category.find_or_create_by(name: name) if name.present?

Step 14

Edit an existing product and change the name to something that does not exist in the database. Update the product. We can now add a new category.

Step 15

In application.js, add:

//= require jquery-ui

It will look like this:

//= require jquery
//= require jquery-ui   
//= require jquery_ujs
//= require turbolinks
//= require_tree .

Step 16

Reload the new product page. You will get the error:

Couldn't find file 'jquery-ui'


gem 'jquery-ui-rails'

to Gemfile and bundle.

Step 17


jQuery(function() {
  return $('#product_category_name').autocomplete({
    source: ['apple', 'apricot', 'avocado']

to products.js. Delete

Step 18

Reload the new product page and enter 'a' for the category name, you see the drop down values for the autocomplete. It looks ugly. Let's fix that. Change the products.scss:

// Place all the styles related to the products controller here.
// They will automatically be included in application.css.
// You can use Sass (SCSS) here:
ul.ui-autocomplete {
  position: absolute;
  list-style: none;
  margin: 0;
  padding: 0;
  border: solid 1px #999;
  cursor: default;
  li {
    background-color: #FFF;
    border-top: solid 1px #DDD;
    margin: 0;
    padding: 0;
    a {
      color: #000;
      display: block;
      padding: 3px;
    a.ui-state-hover, a.ui-state-active {
      background-color: #FFFCB2;

Step 19

Reload the new product page. You can see the styling for the auto dropdown box. Change product form:

<%= f.text_field :category_name, data: { autocomplete_source: Category.order(:name).map(&:name)} %>

to provide the data source.

Step 20

Go to the new product page and view page source.

 <input data-autocomplete-source="[&quot;Beverages&quot;,&quot;Board Games&quot;,&quot;Books&quot;,&quot;Breads&quot;,&quot;Canned Foods&quot;,&quot;Clothes&quot;,&quot;Computers&quot;,&quot;Dry Foods&quot;,&quot;Frozen Foods&quot;,&quot;Furniture&quot;,&quot;Headphones&quot;,&quot;Magazines&quot;,&quot;Music&quot;,&quot;Other Electronics&quot;,&quot;Pastas&quot;,&quot;Portable Devices&quot;,&quot;Produce&quot;,&quot;Snacks&quot;,&quot;Software&quot;,&quot;Televisions&quot;,&quot;Toys&quot;,&quot;Video Games&quot;,&quot;Video Players&quot;,&quot;Videos&quot;]" type="text" name="product[category_name]" id="product_category_name" />

You can see the values for auto complete is escaped.

Step 21

Provide the backend for the autocomplete datasource in the products.js.

jQuery(function() {
  return $('#product_category_name').autocomplete({
    source: $('#product_category_name').data('autocomplete-source')

Reload the new product form and enter b. You will see 5 values in the autocomplete dropdown box.

Step 22

Let's remove the hard-coded autocomplete source and provide a data source as an URL. Create a categories controller.

rails g controller categories

Define the category resource in routes.rb.

resources :categories

Categories controller looks like this:

class CategoriesController < ApplicationController
  def index
    @categories = Category.order(:name).where("name like ?", "%#{params[:term]}%")
    render json:

Step 23

Change the product form:

<%= f.text_field :category_name, data: { autocomplete_source: categories_path} %>

Reload the new product page and enter b for the category name. The auto-complete still works. You can download the source code for this article from We are not using the name term anywhere in our code, how does the params[:term] contain the search term? See the log file when the auto-completion function is triggered:

Started GET "/categories?term=b" for at 2016-12-02 16:02:29 -0800
  ActiveRecord::SchemaMigration Load (0.6ms)  SELECT "schema_migrations".* FROM "schema_migrations"
Processing by CategoriesController#index as JSON
  Parameters: {"term"=>"b"}
  Category Load (1.2ms)  SELECT "categories".* FROM "categories" WHERE (name like '%b%') ORDER BY "categories"."name" ASC
Completed 200 OK in 24ms (Views: 0.4ms | ActiveRecord: 1.9ms)

You see the query parameter named term that has a value b. This is done by the jQuery UI plugin.


In this article, you learned how to implement auto-complete of text field using jquery plugin in Rails 5.


jQuery AutoComplete
jQuery UI Rails Gem

Related Articles

Watch this Article as Screencast

You can watch this as a screencast Auto-Complete Association in Rails 5

Ace the Technical Interview

  • Easily find the gaps in your knowledge
  • Get customized lessons based on where you are
  • Take consistent action everyday
  • Builtin accountability to keep you on track
  • You will solve bigger problems over time
  • Get the job of your dreams

Take the 30 Day Coding Skills Challenge

Gain confidence to attend the interview

No spam ever. Unsubscribe anytime.