Rails migration add_column with existing data

Question

Using Rails and MYSQL. Existing table has a column called c1, I would like to add a column called c2 with data func(c1), func is the model method to deal with c1 data. How should I write the migration? Thanks

Answer 1

1. rails generate migration add_something_to_tablename something:string

2. rake db:migrate

3. Inside that model

add this line

before_save :do_something

add this method

private
  def do_something
    do something with c1
  end