How to cascade Save with CompositeId in NHibernate?

Question

I have a simple three table DB with many-to-many relation.

A(id, Name)
B(id, Name)
AB(AId, BId) references A and B

The corresponding classes:

public class A
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
}

public class B
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
}

public class AB
{
    public virtual A A { get; set; }
    public virtual B B { get; set; }
    public override bool Equals(object obj) { /* routine */ }
    public override int GetHashCode() { /* routine */ }
}

I have made mappings with Fluent NHibernate:

public class AMap : ClassMap<A>
{
    public AMap()
    {
        Id(x => x.Id).GeneratedBy.Identity();
        Map(x => x.Name);
    }
}

public class BMap : ClassMap<B> { /* The same as for A */ }

public class ABMap : ClassMap<AB>
{
    public ABMap()
    {
        CompositeId()
            .KeyReference(x => x.A, "AId")
            .KeyReference(x => x.B, "BId");
    }
}

So now I want to be able to do something like this

var a = new A { Name = "a1" };    
var b = new B { Name = "b1" };    
var ab = new AB { A = a, B = b };

//session.SaveOrUpdate(a);
//session.SaveOrUpdate(b);
session.SaveOrUpdate(ab);

But on SaveOrUpdate I do get TransientObjectException. So to pass over it I need to SaveOrUpdate A and B before saving the AB. But it seems that there should be the other way to persist these objects in a single SaveOrUpdate.

Is there any way to point in AB mapping to Cascade A and B on save operation?

UPDATE:

I removed the List of AB links in A class for clarity. Originally it was:

public class A
{
    public A()
    {
        LinkToB = new List<AB>();
    }

    public virtual int Id { get; set; }
    public virtual string Name { get; set }
    public virtual IList<AB> LinkToB { get; private set; }
}

public class AMap : ClassMap<A>
{
    public AMap()
    {
        Id(x => x.Id).GeneratedBy.Identity();
        Map(x => x.Name);

        HasMany(x => x.LinkToB)
            .KeyColumn("AId")
            .Inverse()
            .Cascade.All()
            .AsBag();
    }
}

// inside the transaction
var a = new A { Name = "a1" };
var b = new B { Name = "b1" };

a.LinkToB.Add(new AB { A = a, B = b });
// session.SaveOrUpdate(b);
session.SaveOrUpdate(a);

Thank you!

Answer 1

Just a side-note, but why did you create a class AB ? If the relationship between these 2 classes does not have any extra properties, then your class 'AB' is not necessary ...

To answer your question: you can define cascade options on a relationship in NHibernate.

In Fluent NHibernate, I guess you'll have to do it like this:

public class FooMap : ClassMap<Foo>
{
    public FooMap()
    {
       HasMany(x => x.Bars).Cascade.AllDeleteOrphan();
    }
}

(note that you have to apply it to your situation, but the collectionmapping returns a property Cascade, so you can define which cascading technique you wish to apply)

Answer 2

I did ask this question at nhibernate user group. And the answer was that there is no way to cascade any operation using composite-id (maybe in the future releases it will be possible).

So I made a workaround. I placed two References (many-to-one with cascading) instead of CompositeId and added Id to the AB table and AB entity. Now it's working and A and B entities are cascading.

Answer 3

I actually managed to get it working very easily, and the code looks too much NOT DRY!

Here is what my case looked like:

public class MappingSample : ClassMap<DomainClass>
{
    public MappingCvTheme()
    {
        CompositeId()
            .KeyProperty(x => x.SomeProperty)
            .KeyReference(x => x.SomeReferencedObjectProperty);

        //here comes the trick, repeat the reference code:
        References(x => x.SomeReferencedObjectProperty).Cascade.All();
    }
}

I hope it helps somebody looking for the same issue in the future.