Rails / Ruby：获取信用卡的最后4位数字

Question

I know I've seen a few similar questions, but none of the solutions have worked for me.

I'm sending a 16 digit number to my Credit Card controller, but I only want the last four. I've been trying every version of [-4..-1] to [14-16] to last(4) and I still get the same error: too many digits. This is the line of code I have right now (:last_4 is sent to controller with 16 digits) :

credit_card_params[:last_4 => credit_card_params[:last_4].last(4)]

The field is an integer field. Here is a sample input:

1234567890987654

And that should produce this:

7654

What am I doing wrong?

UPDATE:

I very much appreciate all of your responses. It u=turns out this is in fact a string. In any case, I've been pulling my hair out over this. Still doesn't work! This is my code, and my controller is still complaining that there's too many chars:

ccNum=credit_card_params[:last_4]
ccNum = ccNum[-4..-1] 
credit_card_params[:last_4 => ccNum]
@credit_card = CreditCard.new(credit_card_params)
respond_to do |format|
  if @credit_card.save #HERE IS THE ERROR!

and this is the code in the form:

<%= f.label :last_4, "Credit Card Number" %><br>
<%= f.number_field :last_4 %>

leaves string 1234123412341235 unchanged, with this error message:

1234123412341235 is out of range for ActiveRecord::Type::Integer with limit 4

If anyone can figure this out I would really appreciate it.

Answer 1

Consider this:

cc = 1111222233334444 # 16 digits in int
cc = cc.to_s # as a string now
cc = cc[-4..-1] # as a string "4444"
cc = cc.to_i #now as a int 4444

Or in just one line

cc = cc.to_s[-4..-1].to_i

Answer 2

Try this:

last_4 = credit_card_params[:last_4].to_s.last(4)

credit_card_params[:last_4] = last_4