Question

Assuming that I have objects similar to this:

public class User
{
    public int UserId { get; set; } 
    public IList<UsersRentingLog> UsersRentLog { get; set; }
}

public class Car 
{
    public int CarId { get; set; } 
    public IList<UsersRentingLog> CarRentLog { get; set; }
}

public class UsersRentingLog
{
    public Userid { get; set; }
    public CarId { get; set; }
}

Now, I want to select all users who rented a particular car..

The sql for this would simply be

select c.*
from [User] u
    inner join UsersRentingLog l on u.userid = l.UserId
    inner join Car c on l.CarId = c.CarId
where u.userid = @UserId

I am trying to get this query to work in QueryOver, NHibernate, and so far, I have got this:

DetachedCriteria dc = QueryOver.of<User>()
    .where(r => r.UserId == userId)
    .JoinQueryOver<UsersRentingLog>(l => l.UsersRentLog)
    .JoinQueryOver<Car>(c => c.Car)
    .DetachedCriteria
    ;

This is selecting, as expected, every single property from all three joined tables, but I actually want to select only Cars.
How can I do this please?

---

Update on correct answer

So, after the answer, I had to make few modifications (mostly minor syntax errors) and thought I’d post the working version.

Because my user doesn’t have a direct reference to the car, I had to modify the alias to go with this

UsersRentingLog logAlias = null; 
var subQuery = QueryOver.of<User>()
    .Where(user => user.UserId == userId)
    .JoinAlias(user => user.UsersRentLog, () => logAlias)
    .subQuery.Select(Projections.Distinct(Projections.Property(() => logAlias.Car.Id)));


var query = _session.QueryOver<Car>();
    query.WithSubquery.WhereProperty(car => car.Id).In(subQuery)
    .TransformUsing(Transformers.DistinctRootEntity)
    .List<Car>();

The above bit, I am using detached criteria, so I rewrote the second code block like so:

DetachedCriteria dc = QueryOver.Of<Car>()
    .WithSubquery.WhereProperty(car => car.Id).In(subQuery)
    .TransformUsing(new NHibernate.Transform.DistinctRootEntityResultTransformer())
    .DetachedCriteria
    ;

Answer 1

Car carAlias = null;
var subQuery = QueryOver.of<User>()
    .Where(user => user.UserId == userId)
    .JoinAlias(user => user.Cars, () => carAlias)
    subQuery.Select(Projections.Distinct(
      Projections.Property(() => carAlias.Id)));

var query = _session.QueryOver<Car>();
query.WithSubquery.WhereProperty(car => car.Id).In(subQuery);
.TransformUsing(Transformers.DistinctRootEntity)
.List<Car>();