Question

I’m trying to order my results by the value in an embedded document.

Consider a model such as:

public class Car
{
    public Guid ID { get; set; }
    public string Name { get; set; }

    public IEnumerable<Passenger> Passengers { get; set; }
}

public class Passenger
{
    public Guid ID { get; set; }
    public virtual string Name { get; set; }
    public virtual int Age { get; set; }
}

I’m trying to query my Car collection, and order by Passenger.Age

My query looks something like:

var results = (from car in _db.GetCollection<Car>("car").AsEnumerable()
              from passenger in car.Passengers
              where car.Name == "Ford"
              orderby passenger.Age).ToList();

With this, I get the following exception:

The SelectMany query operator is not supported.

This is understandably a limitation of the C# mongo driver.
Is there a workaround?

Failing that, how could I order them after my .ToList() ?

Answer 1

You can probably re-write this with AsQueryable() to get an IEnumerable collection from ToList() back, from which you can then further query with any LINQ you want to use, not just the operations directly supported by the MongoCollection:

var passengers = _db.GetCollection<Car>("car").AsQueryable().ToList()
    .Where(car => car.Name == "Ford")
    .SelectMany(ford => ford.Passengers)
    .OrderBy(p => p.Age);

Here’s where you can find the directly supported LINQ operations for the MongoDb C# driver.