MongoDB的.NET不产生对UPSERT _id

Question

我试图UPSERT文档到MongoDB的2.4.4使用.NET驱动程序。这似乎不是自动生成的upserts的_id，尽管它正确地产生在普通嵌入式_id。我怎样才能使驾驶员正常地生成_id？

下面是一个说明该问题的一个小例子。

public class MongoObject
{
    [BsonId(IdGenerator = typeof(StringObjectIdGenerator))]
    [BsonRepresentation(BsonType.ObjectId)]
    public string MongoID { get; set; }

    public int Index { get; set; }
}

var obj = new MongoObject()
{
    Index = 1
};

//This inserts the document, but with a _id set to Null
_collection.Update(Query.EQ("Index", BsonValue.Create(1)), Update.Replace(obj), UpdateFlags.Upsert, new WriteConcern() { Journal = true });

//This inserts the document with the expected autogenerated _id
//_collection.Insert(obj);

Answer 1

当然，我张贴的问题后，立即找到答案。从this answer，解决的办法是一个[BsonIgnoreIfDefault]属性添加到ID。在距离这将是问题的例子：

public class MongoObject
{
    [BsonId(IdGenerator = typeof(StringObjectIdGenerator))]
    [BsonRepresentation(BsonType.ObjectId)]
    [BsonIgnoreIfDefault]    // <--- this is what was missing
    public string MongoID { get; set; }

    public int Index { get; set; }
}