JSON.NET cast error when serializing Mongo ObjectId

Question

I am playing around with MongoDB and have an object with a mongodb ObjectId on it. When I serialise this with the .NET Json() method, all is good (but the dates are horrible

Answer 1

1) Write ObjectId converter

public class ObjectIdConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(ObjectId);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType != JsonToken.String)
            throw new Exception($"Unexpected token parsing ObjectId. Expected String, got {reader.TokenType}.");

        var value = (string)reader.Value;
        return string.IsNullOrEmpty(value) ? ObjectId.Empty : new ObjectId(value);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (value is ObjectId)
        {
            var objectId = (ObjectId)value;
            writer.WriteValue(objectId != ObjectId.Empty ? objectId.ToString() : string.Empty);
        }
        else
        {
            throw new Exception("Expected ObjectId value.");
        }
    }
}

2) Register it in JSON.NET globally with global settings and you not need mark you models with big attributes

            var _serializerSettings = new JsonSerializerSettings()
            {
                Converters = new List { new ObjectIdConverter() }
            };

3) Big advice - don't use ObjectId in your models - use string

[BsonRepresentation(BsonType.ObjectId]
public string Id{ get;set; }