Deserializing object to array

Question

I have a field with mixed type (object or array of object). Now I am trying to deserialize this field into array of object with this

class AssociationSerializer : SerializerBase<Association[]>
{
    public override Association[] Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        var type = context.Reader.GetCurrentBsonType();

        switch (type)
        {
            case BsonType.Array:
                var arraySerializer = new ArraySerializer<Association>();
                return arraySerializer.Deserialize(context, new BsonDeserializationArgs());

            case BsonType.Document:
                var bsonDocument = context.Reader.ToBsonDocument();
                var association= BsonSerializer.Deserialize<Association>(bsonDocument);
                return new[] { association };

            default:
                throw new NotSupportedException();
        }
    }
}

But I am getting this error

System.InvalidOperationException: ReadBsonType can only be called when State is Type, not when State is Value.
at MongoDB.Bson.IO.BsonReader.ThrowInvalidState(String methodName, BsonReaderState[] validStates)
at MongoDB.Bson.IO.BsonBinaryReader.ReadBsonType()
at MongoDB.Bson.Serialization.BsonClassMapSerializer1.DeserializeClass(BsonDeserializationContext context) at MongoDB.Bson.Serialization.BsonClassMapSerializer1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)

Not sure what I am doing wrong.

public class Association
{
    public string Id { get; set; }
    public int Type { get; set; }
}

JSON:

{   
    "association" : [
        {
            "_id" : "b8e0a770-951b-5e85-84a6-8ca8cd0998e0",
            "type" : 0
        }
    ]
}   
    
{
    "association" : {
        "_id" : "08dc1cb0-0f88-4dcf-70db-ff3b8c000003"
    }
}

Answer 1

A simplest approach I see:

 public class AssociationSerializer : SerializerBase<Association[]>
 {
     public override Association[] Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
     {
         var type = context.Reader.GetCurrentBsonType();

         switch (type)
         {
             case BsonType.Array:
                 var arraySerializer = new ArraySerializer<Association>();
                 return arraySerializer.Deserialize(context, new BsonDeserializationArgs());

             case BsonType.Document:
                 var value = BsonSerializer.Deserialize<Association>(context.Reader);
                 return new[] { value };

             default:
                 throw new NotSupportedException();
         }
     }
 }

Answer 2

It seems like the issue might be with the way you are handling the deserialization of the BSON document in the BsonType.Document case. Instead of directly trying to deserialize the Association object from the BsonDocument, try using the BsonSerializer.Deserialize method within a using statement, like this:

case BsonType.Document:
    using (var bsonReader = new BsonDocumentReader(context.Reader.ToBsonDocument()))
    {
        var association = BsonSerializer.Deserialize<Association>(bsonReader);
        return new[] { association };
    }

This ensures that the BsonReader is properly disposed of after use and might resolve the error you are encountering.