How to map a one-to-many relationship in Fluent NHibernate when the foreign key is on the "one" side?

Question

NHibernate

Faced the problem of describing a one-to-many relationship with a non-standard table structure. There are 2 tables FOO and BAR which are related as FOO(1)->BAR(*). At the same time, FOO has an ID_BAR column, which points to a set of records from BAR, and BAR has a non-unique CODE column, the value of which is contained in ID_BAR. You need to bind these tables to the appropriate classes:

class Foo
{
    public virtual IList<Bar> Bars { get; set; }
}
class Bar
{
    public virtual string Code { get; set; }
    public virtual Foo Foo { get; set; }
}

If the foreign key were in BAR, there would be much less problems, and all mapping would be reduced to HasMany, but in this situation, I have no idea how mapping can be done.