REST Operations

Details of REST Operations

A table showing some of the details of REST operations when the the resources are named :items:

CRUD Term	Operation	Helper Method Call	HTTP Operation	Generated Path	Controller Method
Read	Get list of resource items	link_to "Items", items_path	GET	/items	index
Read	Get specific item	link_to "Items", items_path(@item) or link_to "Items", @item	GET	/items/1	show
Read	Get form for creating new item	link_to "Create New Item", new_item_path	GET	/items/new	new
Create	Create new item	form_for(@item)	POST	/items	create
Read	Get completed form for modifying existing item	link_to "Update Item", edit_item_path(@item)	GET	/items/1/edit	edit
Update	Update existing item	form_for(@item)	PUT	/items/1	update
Destroy	Delete existing item	link_to 'Destroy', @item, :confirm => 'Are you sure?', :method => :delete	DELETE	/items/1	destroy

Review Questions

What is wrong?

What is wrong?

rails g scaffold People name:int Text:Gender class:String

What are some possible datatypes for the fields of a Rails scaffold?
Create a Rails project for storing movie reviews using the scaffold software.
What does rake db:migrate do?
In Rails when do you use upper camel casing and when do you use underscore notation?
What is the name and location of the underlying database for a Rails project generated using a scaffold?
If the URL for your Rails project is

http://localhost:3000/movie_reviews.xml

Which views does the Rails scaffold software create?
What does CRUD mean?

Explain the difference between yield and render.
What does the Rails database console do for you? How can you invoke it?

Names Created by Rails Scaffold Software

A resource is information that you are interesting in representing in your online information system.
Here are some examples of resources:

Rails creates the following names for a movie review resource (See Review Question 4):

Resource Name	movie_review
Database Table Name	movie_reviews
Model Name	MovieReview
Controller Class Name	MovieReviewController
Controller File Name	movie_review_controller.rb
View Folder Name	movie_reviews
URLs for Scaffold Site	movie_reviews movie_reviews/1 movie_reviews/new movie_reviews/1/edit

In the preceding table, underscore notation is used for some of the names and upper camel casing for other names.

Here are the names generated by a scaffold if the model name is Person as in Example 8 (Census Example):

Resource Name	person
Database Table Name	people
Model Name	Person
Controller Class Name	PersonController
Controller File Name	person_controller.rb
View Folder Name	people
URLs for Scaffold Site	people people/1 people/new people/1/edit

The Rails scaffolding software knows how to pluralize the name that represents table rows. In this case, Person represents the name of a single row and People represents the entire collection of rows in the table.

Routing

Routes are specified in the file app/config/routes.rb.
So far, the Rails applications we have created have used named routes.
For example, if the controller name is Info and the view name is staff, then the named route used to view this page is
A project created using a scaffold uses a resource based route:

Modifying the Dropdown Menus for Selecting a Date

By default, the year dropdown menu for selecting a date only displays five years on either side of the current year.
To change the displayed years, go into the app/views/new.html.erb. Change the method call
to
Caution: 2009 and 2015 must not be in quotes.

Here are some other options for f.date_select:

# Use month numbers instead of names.
:use_month_numbers => true

# Add month numbers in addition to names.
:add_month_numbers => true

# Use short form of months: Jan, Feb, Mar, ...
:use_short_month => true

# Don't include a dropdown menu for days.
:discard_day => true

# Don't include a dropdown menu for months.
:discard_month => true

# Don't include a dropdown menu for years.
:discard_year => true

Practice Problem: In the MovieReviews Example of Practice Problem 4, modify the form in _form.html so that the year dropdown menu for the movie_release field contains years from 1930 to 2011.

Validations

When a value of the wrong datatype is placed into a model, no error message is given.
For example: if a non-numeric string value is placed into an integer field, it will silently converted to 0.
Validations are a way to get a Rails project to show error messages when illegal values are entered into fields.

Enter these lines into the body of the model in app/model.rb:

validates_presence_of :first_name

validates_length_of :student_id,
    :minimum => 4,
    :maximum => 4

validates_numericality_of :gpa,
    :greater_than_or_equal_to => 0.0,
    :greater_than_or_equal_to => 4.0

Another useful validation for strings is

validates_length_of :password,
   :minimum => 8, :maximum => 20

The textbook discusses validates in Chapter 5. Here are some examples:

validates :title, :presence => true

validates :email, :uniqueness => true

validates :username, :length => { :within => 8..20 }

Practice Problem: In the MovieReviews Example of Practice Problem 4, add validations to the MovieReview model.
Later, we will look at how to validate using validates_format_of. This helper method uses a regular expression to specify the format for validation.

Moving Web Pages over the Internet

In the early days of computer networking (pre 1969), connections between computers were hardwired, and the software to implement the connection was custom tailored to the operating systems of the connected computers.

As the ARPANET (predecessor of the modern Internet) was being built, it became clear that connecting a large number of computers together in one large network required a well designed network architecture.

Gradually the Open Systems Institute (OSI) Seven Layer Model was developed, starting in 1977.
This Seven Layer Model was used to organize network software and allow a wide variety of computer network systems to be connected into a single network.
Of special interest is the HTTP software, which sits at the very top of the Seven Layer Model in the Application layer.
Modern telecommunications systems send data in relatively small packets over the best available transmission line. Then the packets are collected and reassembled to present to the application software on the destination machine.
See this document for a taste of HTTP in the early days:
The Domain Name System (DNS) is a hierarchical naming system for translating symbolic Internet URLs into IP addresses.

Running WEBrick on a Different Port

To start Webrick on a different port:
Then use this URL:
The default port for HTTP is 80. If WEBrick is started as
then the page can be viewed without specifying a page number:
Here is a list of some other well-known ports.
Well-known ports are in the range from 0 to 1023.

HTTP GET vs. POST

Submit information via HTTP GET:
The page information is submitted back to the server in the URL; for example:
Submit information via HTTP POST:
The page information is not submitted back to the server in the URL; it is submitted in the page head.

Representational State Transfer

Some more acronymns:
- Representational state transfer (REST) means using the HTTP GET, POST, PUT, and DELETE operations to implement the CRUD operations:
- REST also assumes
  1. use of a client-server architecture
  2. stateless communication, which means that the neither the views nor the controller remembers the contents of previously submitted pages.
  3. Defining the following in the routes.rb file means defining an entire set of CRUD operations: