This is a review on what I have been through in Week 6 of TeaLeaf Academy.

Rails follow Active Record pattern to perform ORM duties. What’s the Active Record pattern?

• classes to tables
• objects to rows of data within that table
• getters/setters(attributes) to columns in that table

We can create, retrieve, update, and delete the object instances by altering the database table.

To create a table in the database, we can use migrations, rails generate migration create_posts. In the migration file,

1
2
3
4
5
6
7
8
9
10
11

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.string :url
      t.string :title
      t.text :description

      t.timestamps
    end
  end
end

After we run rake db:migrate in the command line, it will create six columns in the database,

1. primary key: id
2. url
3. title
4. description
5. created_at
6. updated_at

Then in the app/models folder, we will create the corresponding model,

1
2

class Post < ActiveRecord::Base
end

The file name will be in singular form, post.rb.

Tips on table name: use the tableize method on the class name. For example, 'Post'.tableize => “posts”.

If we have a Comment model and there is a 1:M association between Post and Comment, a foreign_key column - post_id need to be added to the comments table and it will point to the primary key column in the posts table. Then in the Post and Comment model file, we will do the following changes.

1
2
3
4
5
6
7

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

If there is a Category model and it has a M:M association with Post, a joint model and table will be needed to build up the association. The model file name will be post_category.rb and class name will be PostCategory. To get the table name, 'PostCategory'.tableize and the output is ‘post_categories’. There will be two foreign key columns in the table, post_id and category_id. In the model file, we will set up the has_many :through.

1
2
3
4
5
6
7
8
9
10

class Category < ActiveRecord::Base
  has_many :post_categories
  has_many :posts, through: :post_categories
end

class Post < ActiveRecord::Base
  has_many :comments
  has_many :post_categories
  has_many :categories, through: :post_categories
end

To change the default association name,

1
2
3

class Post < ActiveRecord::Base
  belongs_to :creator, foreign_key: 'user_id', class_name: 'User'
end

This will make post.creator work.

Keyword resources can be used to generate routes. resources :posts will make the following routes available,

1
2
3
4
5
6
7
8
9

   Prefix | Verb  | URI Pattern               | Controller#Action
   -------|-------|---------------------------|------------------
    posts | GET   | /posts(.:format)          | posts#index
          | POST  | /posts(.:format)          | posts#create
 new_post | GET   | /posts/new(.:format)      | posts#new
edit_post | GET   | /posts/:id/edit(.:format) | posts#edit
     post | GET   | /posts/:id(.:format)      | posts#show
          | PATCH | /posts/:id(.:format)      | posts#update
          | PUT   | /posts/:id(.:format)      | posts#update

To create nested routes like /posts/:id/comments/:id, we can use nested resources,

1
2
3

resources :posts, except: [:destroy] do
  resources :comments, only: [:create]
end

except and only keywords can be used to add constrains on the routes.