Question

It seems that when using the following NHibernate query, I do not get a root entity when the left outer join has no records.

ICriteria critera = session.CreateCriteria(typeof(Entity));

criteria.CreateCriteria("SubTable.Property", "Property", NHibernate.SqlCommand.JoinType.LeftOuterJoin);

criteria.Add(Expression.Not(Expression.Eq("Property", value)));

The SQL that I am trying to generate is:

SELECT * FROM BaseTable
LEFT JOIN (
    SELECT * FROM SubTable
    WHERE Property <> value
)Sub ON Sub.ForeignKey = BaseTable.PrimaryKey

Notice that the where clause is inside the left join’s select statement. That way if there arent any maching sub records, we still get a top level record. It seems like NHibernate is producing the following SQL.

SELECT * FROM BaseTable
LEFT JOIN (
    SELECT * FROM SubTable
)Sub ON Sub.ForeignKey = BaseTable.PrimaryKey
WHERE Sub.Property <> value

Is there anyway to achieve that first piece of SQL? I have already tried:

ICriteria critera = session.CreateCriteria(typeof(Entity));

criteria.CreateCriteria("SubTable.Property", "Property", NHibernate.SqlCommand.JoinType.LeftOuterJoin);

criteria.Add(
    Restrictions.Disjunction()
        .Add(Expression.IsNull("Property"))
        .Add(Expression.Not(Expression.Eq("Property", value)));

I am looking for a solution using the Criteria API.

Answer 1

Try this:

var hql = @"select bt
            from BaseTable bt
                left join bt.SubTable subt
                    with subt.Property <> :property";

Or perhaps:

var hql = @"select bt
            from BaseTable bt
                left join bt.SubTable subt
                    where subt.ForeignKey = bt.PrimaryKey
                        and subt.Property <> :property";

Finally:

var result = session.CreateQuery(hql)
                    .SetParameter("property", "whateverValue")
                    .List<BaseTable>();