Question

Using MongoDB I want to keep my model as clean as possible so I decided to follow this approach: http://www.mongodb.org/display/DOCS/CSharp+Driver+Serialization+Tutorial#CSharpDriverSerializationTutorial-RepresentationSerializationOptions

I have a class like:

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

    public Person()
    {

    }
    public Person(string name)
    {            
        this.Name = name;            
    }
}

And inside application_start I have

BsonClassMap.RegisterClassMap<Person>(x =>
{
   x.AutoMap();
   x.IdMemberMap.SetRepresentation(BsonType.ObjectId);
});

But when it run I get a null reference exception on the IdMemberMap. Can someone please tell me if something is wrong?

Answer 1

This is borderline to being a bug in the C# driver. Turns out IdMemberMap is not defined until the class map is “frozen”, for reasons having to do with class hierarchies in which the Id might actually be defined in a base class. One way to work around this is:

BsonClassMap.RegisterClassMap<Person>(cm => {
    cm.AutoMap();
    cm.Freeze();
    cm.IdMemberMap.SetRepresentation(BsonType.ObjectId);
});

Another way to work around is to use GetMemberMap instead of IdMemberMap:

BsonClassMap.RegisterClassMap<Person>(cm => {
    cm.AutoMap();
    cm.GetMemberMap(c => c.Id).SetRepresentation(BsonType.ObjectId);
});