Mongodb select all fields group by one field and sort by another field

Question

We have collection \'message\' with following fields

_id |   messageId |  chainId | createOn

1   |       1     |    A     | 155
2   |       2     |    A     | 1         


        

Answer 1

Replace this line:

final DBObject group = new BasicDBObject("$group", groupFields);

with this one:

final DBObject group = new BasicDBObject("_id", groupFields);