java - 如何在 MongoDB Java 驱动程序中编写带有添加操作的 group by

Question

在下面的查询中，我正在对一个字段进行添加(该字段以 ISO 日期作为值)，然后从该字段中提取小时，然后按小时分组

db.campaigns.aggregate([
    {$group : { _id: {$hour:{$add:['$time', 19800000]}}}}
])


Sample record of the collection    

db.campaigns.findOne()
{
    "_id" : ObjectId("53c7afdab92be74745af9068"),
    "time" : ISODate("2013-03-08T12:25:24.973Z"),
    "type" : "annoying",
    "PINGS" : 143
}

上面的在 Mongo shell 中运行良好，

我正在尝试用 Java 编写此查询

这是我的部分Java代码

DBObject group2Fields = new BasicDBObject();
group2Fields.put("hour", new BasicDBObject("$hour", new BasicDBObject("$add",new BasicDBObject("time",19800000))));
DBObject group2 = new BasicDBObject("_id", group2Fields);
DBObject secondGroup = new BasicDBObject("$group", group2);

我收到“errmsg”:“异常:$表达式内部不允许包含字段”

Answer 1

试试这个:

    DBObject group2Fields = new BasicDBObject();
    BasicDBList addObjects = new BasicDBList();
    addObjects.add("$time");
    addObjects.add(19800000);
    group2Fields.put("$hour", new BasicDBObject("$add", addObjects));
    DBObject group2 = new BasicDBObject("_id", group2Fields);
    DBObject secondGroup = new BasicDBObject("$group", group2);