Composite primary key, foreign key. Reference to object or key?

I have two classes Foo and Bar. The tables in the database look like this:

|Foo|
|id : INT (PK) | bar_id : INT (PK, FK) |

|Bar|
|id : INT (PK) |

Normally I would map it like this:

@Entity
public class Bar
{
    @Id
    @Column(name = "id")
    private int id;

    @OneToMany
    private Set<Foo> foo;
}

@Entity
public class Foo
{
    @EmbeddedId
    private FooPK key;

    @MapsId("barId")
    @ManyToOne
    @JoinColumn(name = "bar_id", referencedColumnName = "id")
    private Bar bar;
}

@Embeddable
public class FooPK
{
    @Column(name = "id")
    private int id;
    @Column(name = "bar_id")
    private int barId;
}

However the id's in FooPK are loosely mapped and need to be connected manually. I would prefer a solution that maps using Objects in stead of loose ids. I tried the following but (of course) it didn't work, but I think it gives an idea of what I would like to achieve:

@Entity
public class Bar
{
    @Id
    @Column(name = "id")
    private int id;

    @OneToMany
    private Set<Foo> foo;
}

@Entity
public class Foo
{
    @EmbeddedId
    private FooPK key;

    @MapsId("barId")
    @ManyToOne
    @JoinColumn(name = "bar_id", referencedColumnName = "id")
    @Access(AccessType.FIELD)
    private Bar getBar()
    {
        return key.getBar();
    }
}

@Embeddable
public class FooPK
{
    @Column(name = "id")
    private int id;

    @Transient
    private Bar bar;

    //....

    @Column(name = "bar_id")
    @Access(AccessType.PROPERTY)
    private int getBarId
    {
        return bar.getId();
    }
}

Another problem with the latter solution is that the getBarId() method in FooPK needs to have a setBarId(Int) method. Setting the Object using the ID can be done by accessing the data access layer, however this (in my opinion) violates the separation of business/