uninitialized constant User::Cartman

[aguipluto]

I'm begining with RoR and I'm developing a new shop app using cartman. The problem is that following the example of the wiki, I have an error triying to add an item to the cart because of this code:

def cart Cartman::Cart.new(id) end

and the error is:

uninitialized constant User::Cartman

what I'm doing wrong?

Thanks for the help