Mapping to a polymorphic list

Question

I'm new to ElasticSearch and trying to use it on my C# application with Nest. I have a class which holds a list of a base type with classes which inherit from it:

public class Automobile
{
    public string ModelName { get; set; }
    public double EngineSize { get; set; }
}

public class Truck : Automobile
{
    public double CarryWeight { get; set; }
}

public class Car : Automobile
{
    public short SaftyStars { get; set; }
}

public class MotorCycle : Automobile
{
    public double DecibleNoise { get; set; }
}

public class AutoDealerShip
{
    public string Name { get; set; }
    [ElasticProperty(Type = FieldType.nested)]
    public IList<Automobile> Models { get; set; }

    public AutoDealerShip()
    {
        Models = new List<Automobile>();
    }
}

I'm trying to map the class so that the actual objects would be saved:

ElasticClient.MapFluent<AutoDealerShip>(m => m.MapFromAttributes().
                                             Properties(prop => prop.
                                             NestedObject<Automobile>(n => n.
                                                 Name(p => p.
                                                 Models.First()).
                                                      MapFromAttributes().
                                                      Dynamic())));

When trying to index data and retrieve it:

private static void IndexPolymorphicObject()
{
    ElasticClient.DeleteIndex(PersonIndex);

    var dealerShip = new AutoDealerShip();
    dealerShip.Name = "Mikes dealership";
    dealerShip.Models.Add(new Truck());
    dealerShip.Models.Add(new Car());
    dealerShip.Models.Add(new MotorCycle());
    ElasticClient.Index(dealerShip);
    ElasticClient.Flush();
}

private static void GetPolyMorphicData()
{
    var result = ElasticClient.Search<AutoDealerShip>(srch => srch.
                                               Query(q => q.MatchAll()));
    var dealerShip = result.Documents.First();
    foreach (var automobile in dealerShip.Models)
    {
        Console.WriteLine("Automobile of type {0}",automobile.GetType());
    }
}

I keep getting back objects of type AutoMobile. Is there a way to store polymorphic data using nest?

Thanks,

Izhar

Answer 1

NEST by default has great support for contravariant results of the documents you store

So if you do

Index<B>()

Index<C>()

Index<D>()

And then do a search for Search<A>(s=>s.Types(B,C,D)) given that all of them derive from A you will get an IEnumerable result with actual instances of B, C and D inside of it.

To get contra/covariance going inside your own document you'll have to do the wiring yourself.

You will have to register a custom jsonconverter on the property to make sure JSON.net deserializes the json back to the actual subtype instead of the supper.