MongoDB custom serializer implementation

Question

I am new to MongoDB, and am trying to get the C# driver to work serializing F# classes. I have it working with the class automapper using mutable F# fields & a parameter

Answer 1

I figured this out in the end. I should have used bsonReader.GetCurrentBsonType() instead of bsonReader.CurrentBsonType. This reads the BsonType in from the buffer rather than just looking at the last thing there. I also fixed a subsequent bug derserializing. The updated method looks like this:

public override object Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options) {
    if (nominalType != typeof(Calendar) || actualType != typeof(Calendar))
        throw new BsonSerializationException();

    if (bsonReader.GetCurrentBsonType() != BsonType.Document)
        throw new FileFormatException();

    bsonReader.ReadStartDocument();
    var id = bsonReader.ReadString("_id");
    bsonReader.ReadName();
    var ser = new ArraySerializer();
    var holidays = (DateTime[])ser.Deserialize(bsonReader, typeof(DateTime[]), null);
    bsonReader.ReadEndDocument();
    return new Calendar(id, holidays);
}