Here are some of my notes from learning rails. I am following the course Web Application Architectures at Coursera. This is seen from perspective of someone used to more desktop applications. I used Ruby as a scripting language for writing small unix tools in the past, but I am not considering myself very up to date.

Setup Project

Have rails autogenerate a bunch of files for a project:

$ rails new myproject

This seems to be the way to create a new model class with corresponding table in database:

$ rails generate scaffold comment post_id:integer body:text

This will to a whole bunch of things. A scaffold from what I can understand is a collection of related:

• Database table
• Model class
• Controller class
• HTML template files representing view

So I will get a table for my comment, a definition of a model class. Actually the model class won’t contain anything, but rails creates methods on it at runtime for me to access variables. That is part of ActiveRecord from what I understand. One can call methods such as:

a_comment     = Comment.new
all_comments  = Comment.all
first_comment = Comment.first

and this will cause SQL statements to be formed fetching the data out from the underlying table.

> Comment.first
    Comment Load (0.1ms)  
    SELECT  "comments".* FROM "comments"   
    ORDER BY "comments"."id" ASC LIMIT 1
    => #<Comment 
        id: 2, 
        post_id: 1, 
        body: "This is my first comment", 
        created_at: "2014-05-05 10:15:52", 
        updated_at: "2014-05-05 10:15:52">

I’ve taken the liberty to format the output for readability. The Controller objects are apparently supposed to be mediators like in Cocoa, but it seems to be used a bit different. They seem to provide the actions the user perform on an object from the user interface. We can use the rake routes to find out what REST services are provided. Or probably this isn’t called REST but is just a bunch of URLs for performing different HTTP actions. But it seems to correspond to what is created in the controllers.

$ rake routes
       Prefix Verb   URI Pattern                                 Controller#Action
     comments GET    /comments(.:format)                         comments#index
              POST   /comments(.:format)                         comments#create
  new_comment GET    /comments/new(.:format)                     comments#new
 edit_comment GET    /comments/:id/edit(.:format)                comments#edit
      comment GET    /comments/:id(.:format)                     comments#show
              PATCH  /comments/:id(.:format)                     comments#update
              PUT    /comments/:id(.:format)                     comments#update
              DELETE /comments/:id(.:format)                     comments#destroy

Inspecting and Debugging

You can interact with your whole rails app from the command line. You don’t need a browser running just run:

$ rails console

Then you can go ahead and call methods such as:

a_comment     = Comment.new
all_comments  = Comment.all
first_comment = Comment.first

mentioned earlier. I recommend using pry it is much better than the standard irb which is a bit antiquated. Install with:

$ gem install pry pry-doc

Then you can run the rails console with:

$ pry -r ./config/environment.rb

pry let you do some neat things like cd and ls into classes or objects.

> cd 42.6
1> round
=> 42
1> exit
>

Great way to drill down into your objects and inspect them. pry wans’t covered in the course I just found that online.

Databases and SQL

You don’t setup the tables in the database yourself directly. Instead rails will generate a schema.rb file. Looking like:

ActiveRecord::Schema.define(version: 20140502112529) do

  create_table "comments", force: true do |t|
    t.integer  "post_id"
    t.text     "body"
    t.datetime "created_at"
    t.datetime "updated_at"
  end
end

This ruby code will generate all the necessary SQL statements to actually create the database.