Chapter 2

Question 1

What is a scaffold generator?

Answer 1

Part of Rails which generates code and thereby functionality

Question 2

How can we generate a new Rails app using a specific version of Rails?

Answer 2

$ rails railsversionnum new appName

Question 3

What is a data model?

Answer 3

A representation of the structures needed by our application

Question 4

What is one way to approach creating a data model?

Answer 4

Identify WHO and WHAT will be needed in the app (ex. users & microblogs), and break down the data/data types needed for each object.

Question 5

Explain the following command:

’$ rails generate scaffold User name:string email:string

Answer 5

This generates a scaffold by passing the ‘scaffold’ command to the ‘rails generate’ script.

The argument of the scaffold command is the singular version of the resource name (in this case, User), together with optional parameters for the data model’s attributes (where the syntax is dataName:dataType)

Note that there is no need to include a parameter for id; it is created automatically by Rails for use as the primary key in the database.

Lastly, note that ‘User’ is SINGULAR! Rails will make it plural by adding an ‘s’ where necessary.

Question 6

Why bother adding ‘bundle exec’ to the following command?

’$ bundle exec rake db:migrate’

Answer 6

‘bundle exec’ ensures that the Rake version specified in our Gemfile is used

Question 7

After creating an object through scaffolding, what is the next step?

Answer 7

Update our database with the new model via a database migration.

Question 8

Having made a model through scaffolding, how can we access it in our browser?

Answer 8

from the root URL, go to /modelName to see the contents of the database and a dialog to edit it.

/modelName/1 - go to user with ID of 1

Question 9

Articulate the process of a typical browser hit to the index page /users using the MVC model

Answer 9

1. The browser issues a request for the /users URL.
2. Rails routes /users to the index action in the Users controller.
3. The index action asks the User model to retrieve all users (User.all).
4. The User model pulls all the users from the database.
5. The User model returns the list of users to the controller.
6. The controller captures the users in the @users variable, which is passed to the index view.
7. The view uses embedded Ruby to render the page as HTML.
8. The controller passes the HTML back to the browser.

Question 10

What does the following do in the routes.rb file?

resources :users

Answer 10

Maps the /users URL to the controller actions for the ‘Users’ resource. This tells the Rails router, which receives a request from a browser, where to route the request to the proper controller action based on the URL

Question 11

What is the definition of a controller in Rails?

Answer 11

A collection of related actions (functions)

Question 12

What is the REST architecture?

Answer 12

The ideas of representational state transfer as identified and named by computer scientist Roy Fielding for developing distributed, networked systems and software applications such as the World Wide Web and web applications.

Question 13

Explain REST in the context of Rails.

Answer 13

Most application components (such as users and microposts) are modeled as resources that can be created, read, updated, and deleted—operations that correspond both to the CRUD (create, read, update, delete) operations of relational databases and to the four fundamental HTTP request methods: POST, GET, PATCH, and DELETE.

Question 14

Explain a RESTful style of development in Rails

Answer 14

The RESTful style of development helps you make choices about which controllers and actions to write: you simply structure the application using resources that get created, read, updated, and deleted.

Question 15

A model file in apps/models generated by scaffolding appears with little to no content; how does it get its functionality?

Answer 15

Via inheritance from ActiveRecord::Base

Question 16

In the ‘users’ controller, what does ‘@users = User.all’ do?

Answer 16

Tells the ‘User’ model to retrieve a list of all the users from the database and place them in the instance variable ‘@users’

Question 17

When an instance variable is assigned to a controller object, where is that instance variable made available?

Answer 17

In the corresponding view, in app/views/controllerName/index.html.erb

Question 18

T/F: scaffolding updates the Rails routes to reflect the new resource.

Answer 18

T; it maps the new resource URL to the resource’s controller

Question 19

Where is the database that we must migrate to, and what is it?

Answer 19

It is a SQLlite database located in /db

Question 20

What is a validation, and where is it defined?

Answer 20

A validation will send an error message if the established criteria are not met. They are stored in the model files in apps/models

The following will cause an error message to be given and the database will not be updated if the length of a new micropost is > 140 characters:

class Micropost < ActiveRecord::Base
  validates :content, length: { maximum: 140 }
end

Question 21

How can an association be defined?

Answer 21

In one model, add ‘has_many :associatedModel’.

In the model to be associated, add ‘belongs_to :ownerModel’

Question 22

T/F: Rails can infer the values to be associated between two models

Answer 22

T; Using the (implicit) ID of one model, Rails can infer that an integer value such as ‘user_id’ is the value to be associated.

Question 23

How can the Rails console be entered and exited?

Answer 23

$ rails console

> > > exit

Question 24

What is the Rails console?

Answer 24

A REPL for interacting with Rails applications (works similar to IRB)

Question 25

What is the inheritance structure for models?

Answer 25

They all inherit from ActiveRecord::Base

Question 26

What is the inheritance structure for controllers?

Answer 26

Controllers inherit from the ApplicationController class (defined in app/controllers/application_controller.rb), which in turn inherits from ActionController::Base

Question 27

Why is the following command necessary after initially deploying to Heroku when the app contains a database?

$ heroku run rake db:migrate

Answer 27

Heroku’s PostgreSQL database back-end needs to be updated with the data models in order to work properly with the app

Question 28

What can be added to a model to make sure that a field is not left blank?

Answer 28

add ‘validates :fieldName, presence: true’