Rails 4: Add Column To An Existing Scaffold - ruby

Question

Yes, this question is flooded on here but most are few years back and I am using Rails 4. I have tried few and it messed up my rails app so I wont take anymore chances.
I have already created a scaffold with fields and I have made many changes to its model, controller and views. Imagine you are working for someone when few weeks later, after you've created a scaffold, they realized they missed out an important column - lol
rails g scaffold Book a:string b:integer
How do I easily add c:date?
Few examples showed running a migration and few says edit the rails console. I am confused with the rails g migration add_this_to_that c:data??
Any reference with your answer is highly appreciated as I'm still learning RoR.

Answer 1

To add new column, you should create migration:
rails g migration add_c_to_books c:date
(note the syntax: add_x_to_y), which will add this file to db/migrate/timestamp_add_c_to_books.rb:
class AddCToBooks < ActiveRecord::Migration
def change
add_column :books, :c, :date
end
end
Now all you need is to run it with:
rake db:migrate
That's it.
You can add multiple columns with:
rails g migration add_c_d_e_to_books c:date d:string e:integer
Which will create following migration:
class AddCDEToBooks < ActiveRecord::Migration
def change
add_column :books, :c, :date
add_column :books, :d, :string
add_column :books, :e, :integer
end
end
Or name it however you want:
rails g migration my_migration
Which will result in clean migration:
class MyMigration < ActiveRecord::Migration
def change
end
end
You are free to specify your directives inside def change.