Parameters/methods in models in rails

I've added an extra method to my model in rails, let's just say it is:

def s开发者_运维问答ubscribed
  true
end

If I create a form with:

<%= f.check_box :subscribed %>

it correctly prints a ticked checkbox, but on submission of the form it says

unknown attribute: subscribed

What am I doing wrong?

---

Add an attribute accessor like this:

class MyModel
  attr_accessor :subscribed
end