ruby - Can Rails Migrations be used to convert data?

Question

I'm trying to convert a column in my Rails app, for arguments sake let's pretend I'm trying to change the age column in my users table to a string representation rather than an int.

In my migration I have this;

def.self up
    add_column :users, :age_text, :string

    users = User.find(:all)

    users.each do |u|
       u.age_text = convert_to_text(u.age)
       u.save
    end
end

def self.convert_to_text(number)
   #code here to convert 1 to 'one' etc
end

But it doesn't seem to be working, is what I'm attempting here even possible with migrations?

Answer 1

What you're trying to do is possible, and I would say the correct thing to do.

You need, though, to reload the column info for the model classes you're updating in the migration, so that Rails knows about the new columns. Try this:

def.self up
    add_column :users, :age_text, :string

    User.reset_column_information 

    users = User.find(:all)

    users.each do |u|
       u.age_text = convert_to_text(u.age)
       u.save
    end
end

On a separate note, please note that if your table is large, doing updates one by one will take a looong time.. Be careful with that.