Rails Resource Routing: Create

Learning Goals

Use Rails to create a resource
Understand the connection between the request body and params

Introduction

In this lesson, we'll continue working on our Bird API by adding a create action, so that clients can use our API to create new birds. To get set up, run:

$ bundle install
$ rails db:migrate db:seed

This will download all the dependencies for our app and set up the database.

HTTP Verb	Path	Controller#Action	Description
GET	/birds	birds#index	Show all birds
POST	/birds	birds#create	Create a new bird
GET	/birds/:id	birds#show	Show a specific bird
PATCH or PUT	/birds/:id	birds#update	Update a specific bird
DELETE	/birds/:id	birds#destroy	Delete a specific bird

Video Walkthrough

Creating New Birds

As always, the first thing we'll need to do to add a new endpoint to our API is update our routes. Following REST conventions, we'll want our clients to make a POST request to /birds to create a new bird. Using the resources method, we can create this route by adding in create to the list of actions we want handled:

Rails.application.routes.draw do
  resources :birds, only: [:index, :show, :create]
end

After updating our routes, run rails routes to check what routes are now available:

Prefix  Verb  URI Pattern           Controller#Action
 birds  GET   /birds(.:format)      birds#index
        POST  /birds(.:format)      birds#create
  bird  GET   /birds/:id(.:format)  birds#show

Awesome! We've successfully added a POST /birds route, which will run the create in our BirdsController. Since we haven't set up that action, let's do so now. For the time being, let's add in a byebug so that we can test out this route and see what we'll need to do in order to create a new bird:

class BirdsController < ApplicationController

  # POST /birds
  def create
    byebug
  end

  # etc
end

Run your server now with rails s.

Now, we'll need to make a POST /birds with some data about the bird we're trying to create. Recall from our schema that our birds table has name and species columns:

create_table "birds", force: :cascade do |t|
  t.string "name"
  t.string "species"
  t.datetime "created_at", precision: 6, null: false
  t.datetime "updated_at", precision: 6, null: false
end

To create a new Bird instance, we'll need to provide values for these two attributes. If we were making this request using fetch, it'd look like this:

fetch("http://localhost:3000/birds", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    name: "Monk Parakeet",
    species: "Myiopsitta monachus",
  }),
});

Let's make that request using Postman (remember to add Content-Type: application/json to the headers as well):

After making the request, we'll hit our byebug debugger, so we can see all the data about the request that we have access to:

    1: class BirdsController < ApplicationController
    2:
    3:   # POST /birds
    4:   def create
    5:     byebug
=>  6:   end
    7:
    8:   # GET /birds
    9:   def index
   10:     birds = Bird.all

From the byebug session, let's see how we can get access to the data we need to handle this request. Remember, our goal in this action is to create a new bird and send the new bird object in the response, so ultimately, we'll want some code like this:

def create
  bird = Bird.create(name: ???, species: ???)
  render json: bird, status: :created
end

The status: :created option will send a 201 status code, which indicates that the request has succeeded and has led to the creation of a resource.

To fill in the blanks, we'll need to figure out how to get data from the body of the request, where our client sent the name and species for this new bird.

In the byebug session, we can access the entire request object by using the request method:

(byebug) request
#<ActionDispatch::Request POST "http://localhost:3000/birds" for ::1>

This request object has all kinds of info about what was sent in the request. Try some of these methods out in your byebug session:

request.request_method
request.headers["Content-Type"]
request.body.read

The last one, request.body.read, will read the body of the request as a string. Nice! We could take it a step further, and parse that string as json:

(byebug) JSON.parse(request.body.read)
{"name"=>"Monk Parakeet", "species"=>"Myiopsitta monachus"}

This will return a Ruby hash of key-value pairs by parsing the JSON string from the request body. However, that's a lot of steps for a fairly common task as a Rails developer. Wouldn't it be nice if there was a bit of ✨ Rails magic ✨ to make it easier to access that parsed request data? Enter the params hash!

Using Params

We can more easily access all the information from the request body by using params:

(byebug) params
#<ActionController::Parameters {"name"=>"Monk Parakeet", "species"=>"Myiopsitta monachus", "controller"=>"birds", "action"=>"create", "bird"=>{"name"=>"Monk Parakeet", "species"=>"Myiopsitta monachus"}} permitted: false>

We've seen params once before, as a way to access the dynamic part of the URL:

# GET /birds/:id
def show
  # params[:id] refers to the dynamic part of our route, defined by :id
  # a request to /birds/2 would give params[:id] a value of 2
  bird = Bird.find_by(id: params[:id])
  render json: bird
end

Here, we can also see all the data from the body of our request added to this params hash as well! Let's use that to create our bird. Exit the byebug session by typing continue or c and hit enter. Then, update your controller action like so:

def create
  bird = Bird.create(name: params[:name], species: params[:species])
  render json: bird, status: :created
end

Back in Postman, send the same request through. Now, you should see a response in Postman with the newly created bird! You should also see in your Rails server log the SQL that was executed when the bird was created:

Started POST "/birds" for ::1 at 2021-05-02 10:09:03 -0400
   (0.1ms)  SELECT sqlite_version(*)
Processing by BirdsController#create as */*
  Parameters: {"name"=>"Monk Parakeet", "species"=>"Myiopsitta monachus", "bird"=>{"name"=>"Monk Parakeet", "species"=>"Myiopsitta monachus"}}
  TRANSACTION (0.1ms)  begin transaction
  ↳ app/controllers/birds_controller.rb:5:in `create'
  Bird Create (2.0ms)  INSERT INTO "birds" ("name", "species", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["name", "Monk Parakeet"], ["species", "Myiopsitta monachus"], ["created_at", "2021-05-02 14:09:03.955909"], ["updated_at", "2021-05-02 14:09:03.955909"]]
  ↳ app/controllers/birds_controller.rb:5:in `create'
  TRANSACTION (0.9ms)  commit transaction
  ↳ app/controllers/birds_controller.rb:5:in `create'
Completed 201 Created in 15ms (Views: 0.5ms | ActiveRecord: 4.1ms | Allocations: 4408)

Success!

Experiment using Postman and byebug. What would you change if you wanted to add additional keys to the params hash? What would you expect the server to return if the new bird wasn't created successfully?

Conclusion

We've now seen how to handle the create action, and take data from the body of a request using the params hash. When Rails receives a request where the Content-Type is set to application/json, it will automatically load the request body into the params hash.

In the next lesson, we'll explore the params hash further, and talk about ways to refactor our code using additional features of the params hash.

Resources

JSON Parameters

cseiter/phase-4-rails-resources-create