Question

Let us say we have a key with values which are polymorphic in their sense. Consider the next sample project:

public class ToBeSerialized
{
    [BsonId]
    public ObjectId MongoId;
    public IDictionary<string, BaseType> Dictionary;
}

public abstract class BaseType
{
}

public class Type1 : BaseType
{
    public string Value1;
}

public class Type2:BaseType
{
    public string Value1;
    public string Value2;
}


internal class Program
{
    public static void Main()
    {
        var objectToSave = new ToBeSerialized
                               {
                                   MongoId = ObjectId.GenerateNewId(),
                                   Dictionary = new Dictionary<string, BaseType>
                                                    {
                                                        {"OdEd1", new Type1 {Value1="value1"}},
                                                        {
                                                            "OdEd2",
                                                            new Type1 {Value1="value1"}
                                                            }
                                                    }
                               };
        string connectionString = "mongodb://localhost/Serialization";
        var mgsb = new MongoUrlBuilder(connectionString);
        var MongoServer = MongoDB.Driver.MongoServer.Create(mgsb.ToMongoUrl());
        var MongoDatabase = MongoServer.GetDatabase(mgsb.DatabaseName);
        MongoCollection<ToBeSerialized> mongoCollection = MongoDatabase.GetCollection<ToBeSerialized>("Dictionary");
        mongoCollection.Save(objectToSave);

        ToBeSerialized received = mongoCollection.FindOne();
    }
}

Sometimes when I try to deserialize it, I get deserialization errors like “Unknown discriminator value ‘The name of concrete type'”. What am I doing wrong? If every value stores a _t why cannot it map it correctly?

Answer 1

Driver should know about all discriminators to deserialize any class without errors. There are two ways to do it:

1.Register it globally during app start:

BsonClassMap.RegisterClassMap<Type1>();
BsonClassMap.RegisterClassMap<Type2>();

2.Or though the BsonKnownTypes attibute:

[BsonKnownTypes(typeof(Type1), typeof(Type2)]
 public class BaseType
 {

 }

If you will use #1 or #2 your deserialization will work correctly.