How to use aggregation in Mongo db Java driver with $match and $in?

Question

How to convert below query into Java code for Mongo Java driver?

db.post.aggregate(
  [
    { $match : {"name" :{'$in': ["michael", "jordan"] } }},
    { $group : { _id : "$game.id" , count : { $sum : 1 } } }
    ]
)

My function is not working:

DBObject match = new BasicDBObject('$match', new BasicDBObject("name", names));

Answer 1

The $in operator takes and array or list of arguments, so any list will basically do. But you need to form the corresponding BSON. Indenting your code helps to visualize:

    BasicDBList inArgs = new BasicDBList();
    inArgs.add("michael");
    inArgs.add("jordan");

    DBObject match = new BasicDBObject("$match",
        new BasicDBObject("name",
           new BasicDBObject("$in", inArgs )
        )
    );

    DBObject group = new BasicDBObject("$group",
        new BasicDBObject("_id","$game.id").append(
            "count", new BasicDBObject("$sum",1)
        )
    );

Answer 2

根据聚合文档 ，您的查询应类似于：

DBObject match = new BasicDBObject('$match', new BasicDBObject('name', new BasicDBObject('$in', names)));