How to build an API using Rails – Part 1

The Rails 5 is out, and of course it came with a lot of new features and improvements, on this tutorial I’m going to cover the Rails API feature.

With all the Javascript stuff coming out, we have a lot of tools for building APIs these days, we have Express, Sails Js and many others. How about Ruby Developers? The most cool feature of Rails 5 is Rails API.

Rails::API is a subset of a normal Rails application, created for applications that don’t require all functionality that a complete Rails application provides. It is a bit more lightweight, and consequently a bit faster than a normal Rails application. The main example for its usage is in API applications only, where you usually don’t need the entire Rails middleware stack nor template generation.

Before you starting doing something you should download the most recent version of Ruby and Rails. I’d recommend using RVM for managing many versions of Ruby.

With all set the first command you should run is:

rails new rails_api_tutorial –api

This command will generate only the basic structure for building an API. It will make the ApplicationController inherit from ActionController::API instead of ActionController::Base. It will also configure the generators to skip generating views, helpers and assets when you generate a new resource.

The next step is to setup the testing stuff like: Rspec, FactoryGirl, Shoulda-Matchers and Rails Controller Testing.

After you adding all those gems your Gemfile should looks like this:


Hit bundle install to install those gems, and check the documentation of each one for more information about putting them to work.

After that you should create a folder called models inside of the spec/ folder, which will contain all the model specs of the API.

With all set, now we will create the first model spec of the application. Inside the spec/models folder create a Ruby file called post_spec.rb

The things the should be tested on model are: Table Fields, Validations, Relationships and any method you’d create. 

We are going to create a simple table for handling our posts, but first we need to create the spec for it:



If we run this spec it will shows an error, because we haven’t implemented the Post model yet. Let’s do it:


We also need to create a migration with all the fields. For creating a migration run:

rails g migration post

After that, open the migration and add the fields:


Now you can migrate:

rails db:migrate

And prepare the migration for the tests:

rails db:test:prepare

After all you can run the command:


And all the tests should  pass:


The first part of this tutorial we covered:

  • The creation of an API only Rails Application
  • The setup of all the testing stuff
  • The creating of the Post model

On the next part of this tutorial I’m going to cover about controllers, how to test them and so on.

The source code of this tutorial is available on my Github:

Do you like this post ? Would you mind to follow it ?

See you guys on the next part.

How to solve: Sorry, you can’t use byebug without Readline (Mac OS)

Byebug is a nice gem for debugging Ruby 2.

The most common problem to happen using this gem is the error: ‘Sorry, you can’t use byebug without Readline‘ , lucky for those running Mac OS, this issue can be simply solved by using this command on terminal:

ln -s /usr/local/opt/readline/lib/libreadline.dylib /usr/local/opt/readline/lib/libreadline.6.dylib

How to get the full path image url with carrierwave gem

In this post I’m going to cover how to get the full path url of an uploaded image using carrierwave gem.

By default carrierwave stores the uploaded images at /uploads/model_name/id/image.png

If you request the image url from the database it will only return the /uploads/model_name/id/image.jpg directory.

What if you need the full path ? Like:

The only thing you need to do is to to set the asset_host in your development/production environment:Captura de Tela 2016-06-05 às 07.56.20.png

After that you need to restart your server and now you can get the full path of the image.

Feel free to ask questions and make suggestions 🙂

See you guys in the next time.

Shoucast Streaming in iOS (Objective-C)

In this post I’m going to cover how to build an iOS app that streams songs from Shoutcast server.

  1.  Open your XCode and Create a new project, select Single View Application and click in Next

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2. Name your app for Shoutcast, and then select Objective-C, and click in Next

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3. Create a button and name it play. This button will start the streaming

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4. Go to View->Assistent Editor->Show Assitent Editor

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5. Create an action called playMusic like the picture below:

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6. Open your ViewCotroller.h to create a property called myStreaming(you should create this property as strong, if you don’t do this the streaming will stop after 2 seconds)

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7. Now go to your ViewController.m and inside the method playMusic you should call the property you defined in your h file.

The First thing you need to have is the streaming URL (shoucast’s urls should have the address and the port), then your need to init the streaming property, after that you should define the source type, in our case is streaming, after all you just need to set shouldAutoPlay to NO and prepare to play the streaming and finally play.

– (IBAction)playMusic:(id)sender {    

 NSURL *myUrl = [NSURL  URLWithString:@”″];

 self.myStreaming = [[MPMoviePlayerController alloc] initWithContentURL:myUrl];

  self.myStreaming.movieSourceType =         MPMovieSourceTypeStreaming;

   self.myStreaming.shouldAutoplay = NO;

   [self.myStreaming prepareToPlay];

   [self.myStreaming play];


After all, run your app and listen to the radio 🙂

That’s all, thanks :).

If you have any questions, feel free to ask.

See you guys next time!

Cpf_Validation Gem

Some days ago I released my first gem for CPF validation.

I’ve seen many gems which do the same but the authors seem to no update them.

You can help me to improve this gem by sending a pull request on github:


As gem:

# in Gemfile
gem 'cpf_validation'

# Run bundler
$ bundle install


Validating a CPF attribute:

class Patient < ActiveRecord::Base
  validates_cpf :cpf_attr
  # or
  validates :cpf_attr, :cpf => true

Validating an attribute that can store CPF:

class Customer < ActiveRecord::Base
  validates_cpf :cpf_attr
  # or
  validates :cpf_attr, :cpf => true

Regular validation options:

:allow_nil   - Allows a nil value to be valid
:allow_blank - Allows a nil or empty string value to be valid
:if          - Executes validation when :if evaluates true
:unless      - Executes validation when :unless evaluates false
:on          - Specifies validation context (e.g :save, :create or :update). Default is :save

Working with Sinatra – Part 2

In the last post I showed how to install Sinatra and how to write a simple code. In these post I’m going to cover Views. View is the V of MVC pattern.

First of all you need to create a folder called views

mkdir views

In this folder you’ll put all your views files .erb or .haml.

To render a view you need to define the format of the view (.erb or .haml) and the name of your view.


get '/' do
  erd :index

This code will render a view called index in the views folder.

Obs: You need to create a view called index.rb in your views folder.

You can also define a template in your views folder and use it in some of your views


get '/' do
  erb :index , layout: :post

This code will render the view index with the post layout (views/post.rb)

There are  many availble options in the options hash.

Here all of them:

List of locals passed to the document. Handy with partials. Example: erb "<%= foo %>", :locals => {:foo => "bar"}

encoding to use if uncertain. Defaults to settings.default_encoding.

Views folder to load templates from. Defaults to settings.views.

Whether to use a layout 
(true or f   alse). If it's a Symbol, specifies what template to use. Example: erb :index, :layout => !request.xhr?

Content-Type the template produces. Default depends on template language.

Scope to render template under. Defaults to the application instance. If you change this, instance variables and helper methods will not be available.

Template engine to use for rendering the layout. Useful for languages that do not support layouts otherwise. Defaults to the engine used for the template. Example: set :rdoc, :layout_engine => :erb

Special options only used for rendering the layout. Example: set :rdoc, :layout_options => { :views => 'views/layouts' }

In the third part of this post we will start coding a simple blog application.

See ya!

Working with Sinatra – Part 1

Sinatra is a DSL for creating quickly web applications in Ruby.

It’s true you can build many web applications with Ruby on Rails, but sometimes you don’t need too much, there are situations you need a simple application and RoR seems to be too much to solve it.

Install the gem

gem install sinatra

Create a ruby file

# mywebapp.rb
require 'sinatra'

get '/' do
  'Hello Sinatra'

Run it

ruby mywebapp.rb

Sinatra runs on http://localhost:4567 as default.

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This defines a simple HTTP method paired with a URL matching pattern. In this case, in the root page it will show a greeting.

get '/' do
  'Hello, Sinatra'

In part two of this post we will work with Views/Templates.