无法将sql函数的返回类型设置为我的类

I have an MVC app which uses linq to sql. I just imported a function from the database to my dbml file. I also added a class that I want to use as a return type for this function. However when I look through the dropdown list for return types (in the designer), my new class is not there (but various other classes are). Just to make sure, I closed and reopened the dbml file and restarted VS, but I still can't see my new class available as an option for the return type.I have an MVC app which uses linq to sql. I jus