Using MongoCollection.Group function to fetch the data from mongodb. But the returned data is partial. It always is one ducument. But in fact it should return several documents after grouping. I can get several documents by group command in client tool of mongodb. But by this api, I can not get full data. It is very strange. Maybe it will always return one object and there are several documents in that object. But it doesn't. Hope some one can help me to resolve this question. Thanks very much indeed.