Question

我用Java编写了这个MongoDB查询：

DBObject group1 = new BasicDBObject();
group1.put("_id",  new BasicDBObject("invoiceNo", "$invoiceNo")
      .append("invoiceDate", "$invoiceDate")
      .append("count", new BasicDBObject("$sum",1)));

DBObject group2 = new BasicDBObject();
group2.put("_id", new BasicDBObject("invoiceNo", "$_id.invoiceNo")
      .append("count", new BasicDBObject("$sum",1)));

AggregationOutput output = dummyColl.aggregate(new BasicDBObject("$group", group1), 
       new BasicDBObject("$group", group2));

，代码是

com.mongodb.CommandFailureException: { "serverUsed" : "localhost/127.0.0.1:27017" , "errmsg" : "exception: invalid operator '$sum'" , "code" : 15999 , "ok" : 0.0}
at com.mongodb.CommandResult.getException(CommandResult.java:71)
at com.mongodb.CommandResult.throwOnError(CommandResult.java:110)
at com.mongodb.DBCollection.aggregate(DBCollection.java:1308)

它给出错误

    SELECT dfl.mydate, dfl.firststart, dfl.lastend, fa.ActivityA, sa.ActivityB 
    FROM
    (select s.mydate, firststart, lastend FROM
    (SELECT mydate, MIN(starttime) as firststart from target GROUP by mydate) s
    iNNER JOIN
    (SELECT mydate, MAX(EndTime) as lastend from target GROUP by mydate) e
    ON s.mydate = e.mydate) AS dfl
    INNER JOIN
    target fa on dfl.mydate = fa.mydate and dfl.firststart = fa.starttime
    INNER JOIN
    target sa on dfl.mydate = sa.mydate and dfl.lastend = sa.EndTime

请帮我弄清楚错误。

Answer 1

在您的代码中

group1.put("_id",  new BasicDBObject("invoiceNo", "$invoiceNo")
  .append("invoiceDate", "$invoiceDate")
  .append("count", new BasicDBObject("$sum",1)));

类似于

$group: { 
  "_id": 
    { 
      "invoiceNo": "$invoiceNo",
      "invoiceDate": "$invoiceDate", 
      "count": { "$sum", 1 } 
    } 
}

但你需要的是

$group: { 
  "_id": { "invoiceNo": "$invoiceNo", "invoiceDate": "$invoiceDate" },
  "count": { "$sum", 1 } 
}

所以第一个查询将是

group1.put("_id",  new BasicDBObject("invoiceNo", "$invoiceNo")
  .append("invoiceDate", "$invoiceDate");
group1.put("count", new BasicDBObject("$sum", 1));

而第二个

group2.put("_id", new BasicDBObject("invoiceNo", "$_id.invoiceNo"));
group2.put("count", new BasicDBObject("$sum", 1));

与MongoDB Java驱动程序聚合的组和总和

1 个答案: