This is my setup. I have a table user where all user with password and so on are set. The customer table has some customer related data. The user_id is the foreign key to relate the customers to the user.
On of the column in the customer table is the customernumber. These numbers has to be uniq for each user_id.
Is this a legacy database you're trying to use with Rails? It doesn't appear to follow Rails conventions.
In this example, is "customer" a unique auto-generated identifier? If so, why do you need "customernumber" to also be unique? If not, what is it?