NHibernate Projections - how to project collections

Question

Have a scenario where I need to only select a single/few columns from an entity, but multiple children in a query. I have been trying with projections but getting an error on the collections property. This is such a normal situation, yet cannot find info on projecting collections - only properties.

Customer customerAlias = null;
Order orderAlias = null;
 var list = _session.QueryOver<Customer>(() => customerAlias)
                    .JoinAlias(x => x.Orders, () => orderAlias, JoinType.LeftOuterJoin)
                    .Select(
                       Projections.Property(() => customerAlias.Name),
                       Projections.Property(() => customerAlias.Orders))//this is the issue
                   .List<object>();

Error returned is:

System.IndexOutOfRangeException : Index was outside the bounds of the array

possible duplicate of [NHibernate QueryOver projections - projecting collections to DTO](http://stackoverflow.com/questions/10535961/nhibernate-queryover-projections-projecting-collections-to-dto) — Baz1nga, May 12 '12 at 21:14

score 3 · Accepted Answer · answered Jun 09 '12 at 08:21

3

Cannot be done in NH 3.3. https://nhibernate.jira.com/browse/NH-3176

answered Jun 09 '12 at 08:21

Samuel Goldenbaum

18,391
17
66
104

score 2 · Answer 2 · answered May 20 '12 at 13:20

How about reversing the query (assuming that Order has a Customer property):

var list = _session.QueryOver<Order>()
                .Select(
                   Projections.Property(o => o.Customer.Name),
                   Projections.Property(o => o.OrderProperty1),
                   Projections.Property(o => o.OrderProperty2)) // etc..
               .List<object[]>();

NHibernate Projections - how to project collections

2 Answers2

Linked