Hi,
I'm an nHibernate novice at the moment, and have been advised to post
here from the Fluent group to see if you guys can suggest an efficient
mapping or some SQL for a multi parent relationship. Then the Fluent
guys can help me translate any suggestions you have into Fluent code
(if appropriate).
The scenario...
I have a legacy database with two tables which allow nodes to map to
other nodes in a hierarchy. Simplified,
the tables are:
NodesTable (NodeId, Name)
ParentsTable (NodeId, ParentId)
This can modelled in a single entity and its map (please excuse the
map being Fluent nHibernate code!):
public class Node
{
public virtual decimal NodeId { get; set; }
public virtual string Name { get; set; }
public virtual IList<Node> Parents { get; set; }
public virtual IList<Node> Children { get; set; }
}
public class NodeMap : ClassMap<Node>
{
HasManyToMany(x => x.Parents)
.ParentKeyColumn("ChildID")
.ChildKeyColumn("ParentID")
.Inverse();
HasManyToMany(x => x.Children)
.ParentKeyColumn("ParentID")
.ChildKeyColumn("ChildID");
}
This maps fine, and the collections all contain the correct parents
and children
The application requires that the "downward" (child) relationships for
each node are shown in a tree view (and nodes with many parents are
indicated as "shared" with other nodes in the tree). I'm retrieving
this initial "tree"
with:
public IList<Node> GetNodes()
{
var query = from nodes in Session.Linq<Node>()
orderby nodes.Name ascending
select nodes;
return query.ToList();
}
Now to the problem....
The tree view shows the nodes correctly, but it is *very* slow even
with only 50 or so records in each table. When configuring the maps
Parents and Children maps to eagerly load you can see a just how bad
the performance is - many queries are executed in both directions
(each node's parents and each node's children)
Perhaps this can be solved by enhancing the session query? Or by
manipulating each map's FetchType? Being an nHibernate novice, I'd
really appreciate any guidance you guys have.
Boz
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