Fluent NHibernate one-to-many with intervening join table? - nhibernate

Question

I'm having trouble getting the Fluent Nhibernate Automapper to create what I want. I have two entities, with a one-to-many relationship between them.
class Person
{
public string name;
IList<departments> worksIn;
}
class Department
{
public string name;
}
The above is obviously bare bones, but I would be expecting to generate the fleshed out schema of:
Person{id, name}
Department{id, name}
PersonDepartment{id(FK person), id(Fk Department)}
Unfortunately, I am instead getting:
Person{id, name}
Department{id, name, personid(FK)}
I don't want the FK for Person included on the department table, I want a separate join/lookup table (PersonDepartment above) which contains the primarykeys of both tables as a composite PK and also Fks.
I'm not sure if I am drawing up my initial classes wrong (perhaps should just be LIst workIn - representing ids, rather than List worksIn), or if I need to manually map this?
Can this be done?

Answer 1

The way the classes have been structured suggests a one-to-many relationship (and indeed that's how you describe it in your question), so it should not be a surprise that FNH opts to model the database relationship in that way.
It would be possible, as you suggest, to manually create a many-to-many table mapping. But, is this definitely what you want?
I tend to find that pure many-to-many relationships are quite rare, and there is usually a good case for introducing an intermediate entity and using two one-to-many relationships. This leaves open the possibility of adding extra information to the link (e.g. a person's "primary" department, or perhaps details of their office within each of their departments).
Some example "bare-bones" classes illustrating this kind of structure:
public class Person
{
public int Id { get; set;}
public string Name { get; set;}
public IList<PersonDepartment> Departments { get; set; }
}
public class PersonDepartment
{
public int Id { get; set; }
public Person Person { get; set; }
public Department Department { get; set; }
public bool IsPrimary { get; set; }
public string Office { get; set; }
}
public class Department
{
public int Id { get; set; }
public IList<PersonDepartment> Personnel { get; set; }
public string Name { get; set; }
}