Question

NHibernate Linq is producing an unexcepted query. Here are my class mappings:

public class OrderClassMap : ClassMap<Order> {
    public OrderClassMap() {
        Id(x => x.PersistenceId).Column("RowId").GeneratedBy.Assigned();
        Version(x => x.PersistenceVersion).Column("RowVersion");
        Map(x => x.OrderId).Generated.Insert().Not.Update();
        Map(x => x.OrderDate);
        References(x => x.Overseer).Column("OverseerId").PropertyRef(x => x.OverseerId);
        References(x => x.Overseer2).Column("OverseerId2").PropertyRef(x => x.OverseerId2);
    }
}

public class OverseerClassMap : ClassMap<Overseer> {
    public OverseerClassMap() {
        Id(x => x.PersistenceId).Column("RowId").Generated.Assigned();
        Version(x => x.PersistenceVersion).Column("RowVersion");
        Map(x => x.OverseerId).Generated.Insert().Not.Update();
        Map(x => x.Name);
        Map(x => x.Email);
    }
}

Here is the Linq query I have:

var orders = session.Query<Order>()
                    .Where(o => ((o.Overseer.OverseerId == 1) || (o.Overseer.OverseerId == 2)))
                    .Fetch(o => o.Overseer)
                    .Fetch(o => o.Overseer2);

The SQL query that is generated is not what I would expect. Instead of doing a left outer join, it does a cartesian join. Here is a shortened example of the query NHibernate produces:

SELECT ...
FROM Orders o LEFT OUTER JOIN
     Overseers v1 ON o.OverseerId = v1.OverseerId LEFT OUTER JOIN
     Overseers v2 ON o.OverseerId2 = v1.OverseerId,
     Overseers v3,
     Overseers v4
WHERE o.OverseerId = v3.OverseerId AND
      o.OverseerId2 = v4.OverseerId AND
      (v3.OverseerId = 1 OR v4.OverseerId = 1)

The query I expected would be like:

SELECT ...
FROM Orders o LEFT OUTER JOIN
     Overseers v1 ON o.OverseerId = v1.OverseerId LEFT OUTER JOIN
     Overseers v2 ON o.OverseerId2 = v1.OverseerId
WHERE (v1.OverseerId = 1 OR v2.OverseerId = 1)

I think it is doing this because I have a legacy database and am using PropertyRef in my mapping. Is there any way to fix this unexpected behavior? Why does NHibernate behave this way? It doesn’t make sense to me because by specifying PropertyRef, I’m saying “Use this key instead of the primary key”.

Answer 1

Try using QueryOver<>, and specify the left outer join.