Come applicare l'attributo BsonRepresentation per convenzione quando si utilizza MongoDB

Sì, l'ho notato anch'io. L'attuale implementazione della StringObjectIdIdGeneratorConvention non sembra funzionare per qualche motivo. Eccone uno che funziona:

public class Person
{
    public string Id { get; set; }
    public string Name { get; set; }
}

public class StringObjectIdIdGeneratorConventionThatWorks : ConventionBase, IPostProcessingConvention
{
    /// <summary>
    /// Applies a post processing modification to the class map.
    /// </summary>
    /// <param name="classMap">The class map.</param>
    public void PostProcess(BsonClassMap classMap)
    {
        var idMemberMap = classMap.IdMemberMap;
        if (idMemberMap == null || idMemberMap.IdGenerator != null)
            return;
        if (idMemberMap.MemberType == typeof(string))
        {
            idMemberMap.SetIdGenerator(StringObjectIdGenerator.Instance).SetSerializer(new StringSerializer(BsonType.ObjectId));
        }
    }
}

public class Program
{
    static void Main(string[] args)
    {
        ConventionPack cp = new ConventionPack();
        cp.Add(new StringObjectIdIdGeneratorConventionThatWorks());
        ConventionRegistry.Register("TreatAllStringIdsProperly", cp, _ => true);

        var collection = new MongoClient().GetDatabase("test").GetCollection<Person>("persons");

        Person person = new Person();
        person.Name = "Name";

        collection.InsertOne(person);

        Console.ReadLine();
    }
}