Linq: select property collection

Question

I have two classes:

public class Person
{
   public int Id{get;set;}
   public string Name{get;set;}
   public List<Order> Orders{get;set;}
}
public class Order
{
   public int Id{get;set;}
   public string Data{get;set;}
   public decimal Sum{get;set;}
}

I use Nhibernate Linq. If I want to get total sum of orders filtering by Persan.Name I do this:

var result = (from person in personRepository.Query
             from order in person.Orders
             where person.Name.Contains("off")
             select order).Sum(order => order.Sum);

How can I do the same using fluent syntax?

Answer 1

Try this:

var result = personRepository.Query
    .Where(person => person.Name.Contains("off"))
    .SelectMany(person => person.Orders)
    .Sum(order => order.Sum);

If this solution throws an ArgumentNullException when there are no orders selected try this two step solution:

var orders = personRepository.Query
    .Where(person => person.Name.Contains("off"))
    .SelectMany(person => person.Orders);
var result = orders.Any()
    : orders.Sum(order => order.Sum)
    ? 0;