How to do NHibernate queries with reference's id as criterion?

I'm trying to do a query through NHibernate where the criterion for the result depends on a referenced table's ID. How do I do this? Let's look at a simple example:

public class Foo
{ 
    public int Id { get; set; }
    public string Name { get; set; }
    public Bar ReferencedBar { get; set; }
}    

public class Bar
{ 
    public int Id { get; set; }
    public string Name { get; set; }
}

Foo is then mapped to Bar:

public class FooMapping : ClassMap<Foo>
{
    public FooMapping()
    {
        Id(c => c.Id).GeneratedBy.HiLo("1");
        Map(c => c.Name).Not.Nullable().Length(100);
        References(c => c.Bar);
    }
}

Now I want to get all Foo's from the Database which reference a specific Bar by id. This function is using Criteria, but please 开发者_C百科give examples using something else if you feel it's better:

public IList<Foo> GetAllFoosReferencingBar(int barId)
{
    using (var tx = Session.BeginTransaction())
    {
        var result = Session.CreateCriteria(typeof(Foo))
            .Add(Restrictions./* foo.ReferencedBar == id */) // <-- How to add restriction using id? 
            .List<Foo>();
        tx.Commit();
        return result; 
    }
}

When I try to do this with, I get the exception:

.Add( Restrictions.Eq( "ReferencedBar", 32 ) );

Type mismatch in NHibernate.Criterion.SimpleExpression: ReferencedBar expected type Bar, actual type System.Int32

I do not have a reference object to Bar with id 32 yet and do not want to create one...

---

If Bar is lazy-loadedable (it is by default) then you can "Load" a proxy of Bar with its Id. You can pass that proxy instance as your reference to Bar in the criteria:

 var result = Session.CreateCriteria(typeof(Foo))
     .Add(Expression.Eq("ReferenceBar", Session.Load<Bar>(barId)))
     .List<Foo>();

This results in the SQL query you expect without having to join to Bar.

---

CreateAlias should help you out, like so:

 var result = Session.CreateCriteria(typeof(Foo))
     .CreateAlias("ReferencedBar", "bar")
     .Add(Expression.Eq("bar.Id", barId))
     .List<Foo>();