NHibernate QueryOver distinct - nhibernate

Question

I have this
scenario:
class User
{
Id,
UserName
}
class UserRelationship
{
User GroupUser,
User MemberUser
}
and query
var query = QueryOver.Of<UserRelationship>()
.JoinqueryOver(x=>x.MemberUser)
.Where(x=>x.UserName == "TestUser");
Now I want to return List Distinct User, so I cannot do
TransformUsing(Transformers.DistinctRootEntity)
because this will give me the UserRelationship.
I need something like this:
Select distinct user.ID
from UserRelationship relationship
inner join User user on user.ID = relationship.MemberUser_ID
Please help
thanks

Answer 1

Given the classes:
public class User
{
public virtual int Id {get; set;}
public virtual string UserName {get; set;}
}
public class UserRelationship
{
public virtual int Id {get; set;}
public virtual User GroupUser {get; set;}
public virtual User MemberUser {get; set;}
}
And the fluent mappings of:
public class UserMap : ClassMap<User>
{
public UserMap()
{
Id(x=>x.Id).GeneratedBy.Native();
Map(x=>x.UserName);
}
}
public class UserRelationshipMap : ClassMap<UserRelationship>
{
public UserRelationshipMap(){
Id(x=>x.Id).GeneratedBy.Native();
References(x=>x.GroupUser);
References(x=>x.MemberUser);
}
}
You want to retrieve a list of distinct "User" based on "MemberUser" from the UserRelationship class.
var distinctMemberUsers = QueryOver.Of<UserRelationship>()
.Select(x => x.MemberUser.Id);
var users = QueryOver.Of<User>()
.WithSubquery.WhereProperty(x=>x.Id).In(distinctMemberUsers)
This should use a In clause in the SQL to give you a distinct list of User.

Answer 2

I know this post is old but I just came across the same problem and thought I would share an answer I found to be much simpler.
No matter what - NHibernate will have to query multiple rows for each parent object (unless you use a SubSelect instead of a Join). Because of this, we know we're going to get a list of say, 500 objects, when there are really only 100 unique objects.
Since these objects are already queried, and already in memory - why not use LINQ?
Based on this question: LINQ's Distinct() on a particular property the answer with the most +'s gives a very eloquent solution. Create another list, and have LINQ do the distinct comparison. If we could do distinct at the database it would clearly be the better option - but since that's not an option, LINQ seems to be a good solution.