NHibernate: Recursive queries - nhibernate

Question

I've got a basic tree structure that is stored in a single table. Let's say this is my model:
public class TreeNode {
public virtual Guid Id { get; private set; }
public virtual string Name { get; private set; }
public virtual IEnumerable<TreeNode> Contents { get; private set; }
}
and the table:
TREE_NODES
PK_NODE Guid
FK_NODE_PARENT Guid
NODE_NAME Varchar
I want the following implementation where the return value is a TreeNode with the full eagerly loaded tree of its children and their children, etc.
public class Tree {
ISessionFactory _sessions;
public TreeNode GetBy(Guid id) {
using(var s = _sessions.OpenSession())
return s.Linq<TreeNode>().Single(n => n.Id == id);
}
}
How would I do this mapping?

Answer 1

I doubt you can optimize it - there is no recurtion in basic SQL. You can optimize it using server-side procedures (server specific - some servers, like MySQL does not support them) but it still be doubtful as you get non-recursive components.
Probably the best way is to walk down the tree in loading function and force the evaluation. Something like:
public class TreeNode {
public virtual Guid Id { get; private set; }
public virtual string Name { get; private set; }
public virtual IEnumerable<TreeNode> Contents { get; private set; }
}
public class Tree {
ISessionFactory _sessions;
public TreeNode GetBy(Guid id) {
using(var s = _sessions.OpenSession()) {
return LoadSubTree(s.Linq<TreeNode>().Single(n => n.Id == id));
}
}
private LoadSubTree(TreeNode node) {
foreach(var n in node.Contents)
LoadSubTree(n);
}
}
PS. Tree is probably not the best place for ISessionFactory.