AddToSetEach operator won't return the correct query (Builders v 2.4.4) - mongodb

Question

I've some code to update an array (add to set). The code is currently using the legacy builder:
var data = new[] { 10, 20, 30 };
var fieldName = "data";
var oldWay = Update.AddToSetEach(fieldName , new BsonArray(data));
Console.WriteLine($"Old way:\n {oldWay.ToJson()} \n\n");
This works perfectly and prints:
Old way:
{ "$addToSet" : { "users" : { "$each" : [10, 20, 30] } } }
But when trying to use the new Builders class, I can't get it to work correctly. I'm using MongoDB.Driver 2.4.4. My code:
var data = new[] { 10, 20, 30 };
var fieldName = "data";
var newWay = Builders<BsonDocument>.Update.AddToSetEach(fieldName, new BsonArray(data)).ToJson();
Console.WriteLine($"New way:\n {newWay} \n\n");
The output is:
New way:
{ "_t" : "AddToSetUpdateDefinition`2" }
Any thoughts?
Thank you!

Answer 1

I don't think .ToJson() renders the string how you want it to on a FilterDefinition. It used to be a little easier in the old driver.
Someone wrote an extension method though:
public static class MongoExtensions
{
public static BsonDocument RenderToBsonDocument<T>(this UpdateDefinition<T> filter)
{
var serializerRegistry = BsonSerializer.SerializerRegistry;
var documentSerializer = serializerRegistry.GetSerializer<T>();
return filter.Render(documentSerializer, serializerRegistry);
}
}
Then you can
var data = new[] { 10, 20, 30 };
var fieldName = "data";
var newWay = Builders<BsonDocument>.Update.AddToSetEach(fieldName, new BsonArray(data));
var newWayJson = newWay .RenderToBsonDocument().ToJson();
Console.WriteLine($"New way:\n {newWayJson } \n\n");