I am using rails v3.2.2 and I get a strange error when I try to load associated records.
The following is the Terminal input/output I get:
1.9.2-p318
There are two constants called Article on your app. One is your active record class, top level constant. The other is the module
Category::Article.
When you do belongs_to :article, it would seem that rails starts looking for an Article constant in the class the belongs_to is called from so it is finding the wrong one. This causes all sorts of mess, since you obviously can't use an activerecord class and a module interchangeably
Setting :class_name => '::Article' forces the top level Article class to be found instead.