Given a class of type Person

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

The aggregation framework expression trees are currently losing the ObjectId representation.

.Project(x => new { MyId = x.Id })
.Match(x => x.MyId == "54b73ce5e9080a3534370443")

The Match should render the "54b73..." as an objectId in the query, but instead it renders it as a string because we lost the serialization information when we did a projection.