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Rails - Basic Steps II

Database

  • The scaffold generator create a database migration file in root_app/db/migrate
  • rake command execute the migration files
  • The DB to be used is specified in root_app/db/database.yml

Rails environment

  • Development - When the application is created is in this mode, all changes are reflected immediately
    • rails server - Deploy in development mode
    • Use SQLite as part of the development environment 
  • Test - To run the tests
  • Production - When the application is deployed
    • rails server -e production - Deploy in production mode 

Active Record

  • Is a design pattern
  • In Ruby is used as a mean of persisting data
  • Is used to access data stored in relational databases
  • Perform CRUD operations without worrying about the specific underlying database
  • Encapsulates that notion an object-relational mapping (ORM)

Active Record Module

This pattern is provided in a module called ActiveRecord
    • Establish a connection
      • ActiveRecord::Base.establish_connnection,  use the information from root_app/config/database.yml
    • Create database tables
    • Specify association between tables to Ruby classes
    • ActiveRecord::Migration - Incrementally evolve your DB overtime 
    • ActiveRecord::Schema.define - is created in file root_app/db/schema.rb, express its structure programmatically using a portable database-independent (DSL)

Interactive Ruby Shell (IRB)

Is an interpreter that allows real-time experimentation (like in python)

Command:  irb
Command:  quit - to exit

 To have the console in rails
Command:  rails console

 Create an object: p = Post.new(:title => "My post", :body => "Post content")
Save the object: p.save

Create Relationship between models

These are the relationship types:



To apply this relationship to our model:
  1. Go to  root_app/app/models
  2. Open the files *.rb
    • File with the primary key, add the line has_many an the entity with the foreign key in plural.  Ex: has_many :comments
    • File with the foreign key, add the line has_many an the entity with the foreign key in singular.  Ex: belongs_to :post
  3. To delete in cascade, in the entity  with the primary key
    • Add to the line dependent: destroy
    • Ex: has_many : comments, dependent: :destroy
  4. Open the rails console
    • Type p = Post.all and appear the comments related with a post and assigned to variable p.
    • Type p[1].destroy and the second comment will be destroyed with his comment

Create new Routes

  1. Go to  root_app/config
  2. Open the files routes.rb
  3. Add the line to the entity with the foreign key do resources:entity_primray_key
    • Ex: resources :posts do  resources :comments end
  4. Execute the command rake routes

Upload the changes to GIT

  1. git add .
  2. git commit -m "Added associations"
  3. git push origin master

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