I have a class:

public class Foo
{

public ObjectId _id

{ get; set; }

public string Name { get; set; }

public string Summary

{ get; set; }

}

And I have a function for inserting it

public void EditFoo(Foo fooBar)

{ _db["fooBar"].Save(fooBar, SafeMode.True); }

If fooBar._id exists in the database the save function does an update. If fooBar.Id does not exist it seems as if the driver is picking a document in the collection. and replacing it with my content.