w4d1

Question 1

What does the Rails router do?

Answer 1

Receives URLs and decides what to do with them (what paths are valid, what code to run, etc.).

Question 2

What does #resources do in the routes.rb file?

Answer 2

Given the name of a (plural) model name as a symbol, it will generate 7 routes:

HTTP Verb

Path

action

used for

GET /photos index display a list of all photos
GET /photos/new new return an HTML form for creating a new photo
POST /photos create upload and create a new photo
GET /photos/:id show display a specific photo
GET /photos/:id/edit edit return an HTML form for editing a photo
PATCH or PUT /photos/:id update update a specific photo
DELETE /photos/:id destroy delete a specific photo

Question 3

What is the convention for naming controllers?

Answer 3

The plural name of the model with the word “Controller” camel cased after it:

PhotosController, UsersController, etc.

Question 4

How can an HTTP verb be specified in a url helper?

Answer 4

Add a method: argument:

button_to(photo_url(@photo), method: :delete)

Question 5

What are some routing helper methods that controllers and views can use, in this case the ones that would be generated with resources :photos in routes.rb?

Answer 5

method

url

photos_url http://www.example-site.com/photos
new_photo_url http://www.example-site.com/photos/new
photo_url(@photo) http://www.example-site.com/photos/#{@photo.id}
edit_photo_url(@photo) http://www.example-site.com/photos/#{@photo.id}/edit

Question 6

How can we embed query string options in url helpers?

Answer 6

photos_url(recent: true) == http://www.example-site.com/photos?recent=true

Question 7

How can we specify the root of an app?

Answer 7

root to: ‘controllername#action’

In routes.rb

Question 8

What is the command to see the available routes?

Answer 8

$rake routes

Question 9

The following is part of the output from rake routes:

users GET /users(.:format) users#index
POST /users(.:format) users#create

What are the url helpers for these routes? Why are they the same.

Answer 9

You can tack on _url after the name of the left most column to get the routing helper. The helper for both of these is users_url; the router distinguishes between the two based on the HTTP verb that is sent.

Question 10

What is the purpose of a controller?

Answer 10

After the router decides what controller to use, the controller is responsible for making sense of the request and producing the appropriate output.

It’s the controller’s job to ask the model layer to fetch data, to process user input to save new data, and to either build and send a response or redirect the user to a new path.

Question 11

What does the router actually do once it decides on a controller?

Answer 11

It instantiates an instance of that controller and calls the specified action (method) on that instance.

Question 12

Where do controller actions usually get their data from?

Answer 12

From the model class and its instances.

Question 13

Where does the data for ‘params’ come from?

Answer 13

Parsed from the query string of a URL, and/or from an HTML form.

Question 14

What method actually gets the params hash?

Answer 14

ActionController::Base#params

Question 15

How is #permit used to create strong parameters?

Answer 15

It “whitelists” parameters that can be changed. Non-whitelisted attributes cannot be changed:

@post = Post.new(params[:post].permit(:title, :body))

Question 16

Can you use a nested hash to create or update a model instance? Why/why not?

Answer 16

You cannot do so in the controller because of strong parameter limitations.

Question 17

What should strong parameter helper methods be?

Answer 17

Private/protected:

def cat_params
params.require(:cat).permit(:name, :age)
end

Question 18

How do we tell the controller what object we are talking about?

Answer 18

With :id

def update

@cat = Cat.find(params[:id])
@cat.update!(cat_params)
redirect_to cat_url(@cat)   end

Question 19

What does the controller instance do once it has been told what action to call?

Answer 19

It either renders a response (view) or issues a redirect.

Question 20

What happens after the controller instance issues a response?

Answer 20

The request is over and the connection between client-and-server is closed. The controller instance is discarded.

Question 21

What happens to instance variables stored in the controller instance?

Answer 21

Setting instance variables in the controller does not affect the processing of future requests. State is saved either in the database (server-side) or the cookie (client-side). Since instance variables will be lost (in fact the whole controller object is lost) immediately after the response is issued, you cannot use instance-variable data stored from previous requests.

Question 22

Why would non-browser program prefer to have responses to their HTTP requests be delivered in a form like JSON instead of something like HTML?

Answer 22

JSON and similar formats are lightweight and only contain data the program needs, as opposed to the extraneous display information that abounds in HTML. Requests like these are known as API requests.

Question 23

Describe the basic relationship between Rails and JSON.

Answer 23

The model layer converts a model to JSON, and the controller layer returns the JSON to the user.

Question 24

What should all controller actions end with?

Answer 24

Either #render or #redirect_to

Question 25

Is the following controller code valid:

render json: users

Answer 25

Yes, because render merely places something in the response body. If this is part of a JSON API for a non-browser, the JSON representation will suffice.

Question 26

Given the following association, what would the routing that reflects this look like?

# app/models/magazine.rb
class Magazine

Answer 26

config/routes.rb
NewspapersApp::Application.routes.draw do
resources :magazines do
# provides a route to get all the articles for a given magazine.
resources :articles, only: :index
end

# provides all seven typical routes
resources :articles
end