How to use a inner join in Fluent NHibernate to fetch a single property from the right table - nhibernate

Question

I have a query that fetches every property from one table, however the query should fetch one additional property from another table.
I'm using a simple example where querying every property from the second table wouldn't have any affect in performance, however the real situation does have many properties.
This is the queried table model:
public class Car
{
public long Id;
public long SellerId;
public string Name;
public string SellerName;
}
However, in the SellerName property is not being mapped, since this property is in another model:
public class Seller
{
public long Id;
public string SellerName;
}
The Car class mapping is currently as follow:
Property(x => x.Id);
Property(x => x.SellerId);
Property(x => x.Name);
This will create a model like this one:
Car Table
|------------------------------------------------|
|Id | SellerId | Name |
|1 | 1 | Car Number one |
|------------------------------------------------|
Employee Table
|---------------------------|
|Id | Name |
|1 | John Doe |
|---------------------------|
Using a simple query I can easily use an inner join to gather the Car data with the related employee name:
select c.*, p.Name from Car c
inner join Employee e on c.Id = e.EmployeeId
I've already tried this query:
var query = from car in session.Query<Car>()
join employee in session.Query<Employee>() on car.SellerId equals employee.Id
select new Car
{
Id = car.Id,
SellerId = car.SellerId,
Name = car.Name,
ClientName = employee.ClientName
};
But this actually creates two queries in the database, one for the Client table and another one for the Employee one. And this isn't using Linq, which is also a requirement.

Answer 1

First point here is, you have to use virtual properties for NHibernate's behaviour. You could map the relation on your model, for sample
public class Car
{
public virtual long Id { get; set; }
public virtual string Name { get; set; }
public virtual long SellerId { get; set; }
public virtual Employee Seller { get; set; }
}
And your map,
public class CarMap : ClassMap<Car>
{
public CarMap()
{
// map other properties...
// You could map the the SellerId to be easy to access here (just readonly, use the reference to persist)
Map(x => x.SellerId).Column("SellerId").Not.Nullable().ReadOnly();
References(x => x.Seller).Column("SellerId");
}
}
Given you have a right mapped model and you are using Linq, you could use Fetch method from NHibernate.Linq namespace and it will force a join for you avoiding the lazy loading. For sample:
var data = session.Query<Car>()
.Fetch(x => x.Seller)
.ToList();