Introduction

This post shows an example on how to create a simple Rails application that access resources from a MySQL database.

Read this for instructions to set up MySQL on OS X.

Install MySQL gem

Assuming MySQL is installed using Homebrew:

$ env ARCHFLAGS="-arch x86_64" gem install mysql2 -- --with-mysql-config=/usr/local/Cellar/mysql/<version>/bin/mysql_config 

Create Rails App with MySQL Database Access

$ rails new <app> -d mysql

Configure Rails for Database Access

At this point, the database must already exist with all privileges granted to a (preferably) non-root user. The next step is to enter the information in the configuration file:

$ vim config/database.yml

Enter the database, user and password (plus other parameters as necessary):

# MySQL
  # gem install mysql2
  development:
    adapter: mysql2
    host: localhost
    database: <database>
    username: <user>
    password: <password>
    pool: 5
    timeout: 5000

Create Table From Rails

$ rails g scaffold <table> <field1>:<type1> <field2>:<type2> ...
$ rake db:migrate

Test App UI

$ rails s
$ open http://localhost:3000/<table>

In the web browser, you should see a default page that shows the existing records in the specified table, as well as a button to add new records. Test to see if it works.

(Optional) Login to MySQL console to verify that the records are correct.

DRY-er Controller Class

The default controller class created from scaffold contains many repeated parts, which should be re-factored to adhere to the DRY (Don’t Repeat Yourself) principle. The result is a cleaner and much shorter piece of code too. The class is contained in the file app/controllers/<table>_controller.rb, so open it with your favourite text editor and edit away.

The following example shows a DRY-er version of controller class for accessing the database table ‘users’.

First step is to create helper methods representing the database table:

private
  
# Make these helpers available to the view too
helper_method :user, :users
  
def user
  # If the action is new or create...
  if @user = params[:action] =~ /new|create/
	User.new(params[:user])
  else
	User.find(params[:id])
  end
end

def users
  @users = User.all
end

Then the five API calls: index, show, create, update and destroy can be cleaned up to contain 1-2 lines of code only:

respond_to :html, :json, :xml

def index
  respond_with users
end

def show
  respond_with user
end

def create
  user.save
  respond_with user
end

def update
  user.update_attributes(params[:user])
  respond_with user
end

def destroy
  user.destroy
  respond_with user
end

The complete listing:

class UsersController < ApplicationController

  respond_to :html, :json

  def index
    respond_with users
  end

  def show
    respond_with user
  end

  def create
    user.save
    respond_with user
  end

  def update
    user.update_attributes(params[:user])
    respond_with user
  end

  def destroy
    user.destroy
    respond_with user
  end

  private

  # Make these helpers available to the view too
  helper_method :user, :users

  def user
    # If the action is new or create...
    if @user = params[:action] =~ /new|create/
      User.new(params[:user])
    else
      User.find(params[:id])
    end
  end

  def users
    @users = User.all
  end

end

Reference

How to write a Ruby and Rails 3 REST API

Published

30 July 2012

Ruby on Rails 3 REST API Example