How to indexing and searching nested properties of Interface type in NEST - elasticsearch

Question

I have a following document index entity:
[ElasticType(Name = "Document", IdProperty = "Id")]
public class Document
{
[ElasticProperty(Index = FieldIndexOption.NotAnalyzed)]
public string Id { get; set; }
[ElasticProperty(Type = FieldType.Nested)]
public ICustomer Customer { get; set; }
}
where ICustomer can be different types:
public interface ICustomer
{
}
public class Supplier : ICustomer
{
public string Name { get; set; }
//another properties
}
public class Vendor : ICustomer
{
public string Name { get; set; }
//another properties
}
My mapping is:
Client.CreateIndex("Document", c => c
.AddMapping<Document>(m => m
.SearchAnalyzer("standard")
.IndexAnalyzer("standard")
.MapFromAttributes()
.NumericDetection()
.DateDetection();
When I save document to index it saves also nested objects (Supplier or Vendor) serialized correctly.
But I have problem when I'm searching data. I'm getting following exception from newtonsoft:
Type is an interface or abstract class and cannot be instantiated.
I was trying to create custom json converter
public class CustomJsonConvertor : JsonConverter
{
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
serializer.Serialize(writer, value);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (objectType == typeof(Supplier))
{
return serializer.Deserialize(reader, typeof (Supplier));
}
if (objectType == typeof(Vendor))
{
return serializer.Deserialize(reader, typeof(Vendor));
}
throw new NotSupportedException(string.Format("Type {0} unexpected.", objectType));
}
public override bool CanConvert(Type objectType)
{
return objectType == typeof (Supplier) || objectType == typeof (Vendor);
}
}
and register it as:
settings.AddContractJsonConverters(t => typeof(ICustomer).IsAssignableFrom(t) ? new CustomJsonConvertor() : null);
But then I'm receiving exception in ReadJson method, because objectType is of type ICustomer and the conditions if (objectType == typeof(Supplier)) are never true. Parameter existingValue is null in this method, so I have no option how to determine
the correct type.
NOTE: my entities (Vendor, Supplier) are in separated dll (plugin) and I have no direct access to the them while defining Document.
Can you advise what I'm doing wrong or give me some best practice advice how to deal with interface or abstract class inside document index and how to deal with polymorphism?
thanks a lot!

Answer 1

That information is lost, you'll need to inspect the JSON to provide a differentiator.
For hits themselves NEST is able to use _type as a differentiator. For collections inside your document you will have to either write your jsonconverter to instantiate the right type based on a property or instruct Json.NET to write that information for you when serializing automatically.