nHibernate mapping by code - how to populate object tree with nested collections - nhibernate

Question

I can't seem to find a good example of what I want to do, using nHibernate mapping by code:
I have an object "Message" that has a list of "Organisms" and each "Organism" has a list of "Drugs". Please forgive my pseudo example below:
public class Message
List<Organism> Organisms;
public class Organism
List<Drugs> Drugs;
public class Drug
//create our tree structure
var message=new Message();
var drug = new Drug();
var organism = new Organism();
organism.Drugs.Add(drug);
message.Organisms.Add(organism); //now we have a message with one organism child with one drug drug
Using Bags in my class mappings, I am able to correctly save this message object, and have it persist correctly. The problem is when calling Get with the message ID to bring back the message. I am getting "collection is not associated with any session"
As for my mappers, my message has a bag of organisms, which have a bag of drugs.
Does anyone have an example of doing this type of thing with nHibernate mapping by code? I am missing something in my mappers...

Answer 1

you need to do a little more if you want bi-directional mappings.
So I would define a message property on the Organism class. And map that as a reference.
Add Add/Remove properties on the parent class for your collection class so that you can add the element to the list and to also add the this reference to your child object.
public class Message
{
public Int32 Id { get; set; }
public IList<Organism> Organisms { get; protected set; }
public Message()
{
Organisms = new List<Organism>();
}
public void AddOrganism(Organism organism)
{
if (Organisms.Contains(organism))
return;
organism.Message = this;
Organisms.Add(organism);
}
public void RemoveOrganism(Organism organism)
{
if (!Organisms.Contains(organism))
return;
Organisms.Remove(organism);
}
}
public class Organism
{
public Int32 Id {get;set;}
public Message Message { get; set; }
}
With regards to your mappings you need to set the Message.Organisms to a Bag and on the Organism.Message to a ManyToOne. For the next level down, just repeat this.
public class MessageMap
{
public MessageMap()
{
Bag(x => x.Organisms, map =>
{
map.Key(k =>
{
k.Column(col => col.Name("MessageId"));
});
map.Cascade(Cascade.All | Cascade.DeleteOrphans);
},
action => action.OneToMany());
}
}
public class OrganismMap
{
public OrganismMap()
{
ManyToOne(x => x.Message, map =>
{
map.Column("MessageId");
map.NotNullable(false);
});
}
}