RAILS API

Learning Objectives

Practice migrating and seeding a database
Learn how to set up routes both individually, and with resources
Create controller actions to handle requests and return json
Use ActiveRecord models within our controller actions
Use strong params to require and permit certain data
Understand how controller callbacks can help keep our code DRY

Routing

The format of a route is as follows:

get '/route/path/:some_param', to: 'controller#action'

The method is first. This can be any of our http methods (get, post, put, delete)
Then comes a string with the path of the route we are making. Any parameters are specified with a : before them
Next we say where the route should point to by having the name of the controller, a # then the name of the method within the controller that should be called

If you are creating full RESTful routes, you can use the shortcut: resources :resource_name for example doing:

resources :pets

will create the following routes:

Prefix	Verb	URI Pattern	Controller#Action
pets	GET	/pets(.:format)	pets#index
	POST	/pets(.:format)	pets#create
pet	GET	/pets/:id(.:format)	pets#show
	PATCH	/pets/:id(.:format)	pets#update
	PUT	/pets/:id(.:format)	pets#update
	DELETE	/pets/:id(.:format)	pets#destroy

TIP: Running rails routes in your console will list all of the routes in your application.

Controllers

In our controllers we handle the information coming from our request and send out a response. Here we can also interact with our models to retrieve data. We can also then send a response by using the render method. For apis we want to render json to do so we use: render json: { your: "data here" }. An example of this together would be:

def index 
  @pets = Pet.all
  render json: { pets: @pets }
end

Params

To access information being sent with our request, we can use our params. These params have the values for:

The params specified in our routes
Any query params sent with the request
The body data from our request.

We can pretty much use them for everything. If we want to access a specific param, we can do so using bracket notation: params[:id].

When we are using params to either create or update records in our db, we want to make sure we sanitize and restrict what data is being used. To do so we can use something called Strong Params. This tool allows us to require and permit certain parameters in requests.

params.require(:pet)

The above code will make sure that we have a param called pet in our request and return the value of it. If there is no pet param, it will throw a ActionController::ParameterMissing error.

params.permit(:name, :owner, :species)

This code will filter out any params that are not permitted. This way, we can make sure we only use the parameters we want. It is common to see these used together:

def pet_params
  params.require(:pet).permit(:name, :owner, :species)
end

Which would ensure that there is a pet param with only the attributes name, owner, and species. This can then be used to either create or update our pet without worrying about what the user put in:

Pet.new(pet_params)

Controller Callbacks

Often in our controllers patterns arise where we are writing repetitive code. For example, for :show, :update, and :destroy we will always need to find a specific entity by id. To keep our code dry, we can create a method that will preform these actions before we even get to the controller action. We add the method to our controller like any other method:

def assign_pet 
  @pet = Pet.find(params[id])
end

we can then specify to use this method before certain actions at the top of our controller: