java - MongoDB聚合查询转java代码

Question

我正在尝试将mongoDB查询转换为Javacode，但它在mongo中返回正确的值，但是当在java代码中运行时，它没有返回正确的计数值(它返回正确的machineID、errorID，但计数为null，而是count 应返回记录数)。

Mongo 驱动程序名称

mongo-java-driver-3.3.0.jar

MongoDB 查询

 db.getCollection('collectionName').aggregate([
    {"$match" : {"machineID": {"$in": ["1","10"]} , "errorID" : "error5"}},
    {"$group" : {_id : {machineID : "$machineID", errorID : "$errorID"}, count : {$sum  : 1} } },
    {$project : {machineID : "$_id.machineID", errorID : "$_id.errorID", count : "$count", _id : 0}}
])

Java 代码:

AggregateIterable<Document> resultset =dbCollection.aggregate(Arrays.asList(
                new Document("$group", new Document("_id", new BasicDBObject("machineID", "$machineID").append("errorID","$errorID").append("count", new BasicDBObject("$sum",1)))),
                new Document("$project", new Document("machineID", "$_id.machineID").append("errorID", "$_id.errorID").append("count", "$count").append("_id", 0))));

返回值

machine ID -> 100
errorID  -> error3
count  -> null

Answer 1

如果您尝试保持与 JSON 格式示例相同的结构，这会有所帮助:

AggregateIterable<Document> resultset =dbCollection.aggregate(Arrays.asList(
  new Document("$match",
    new Document("machineID", new Document("$in", Arrays.asList("1","10")))
      .append("errorID", "error5")
  ),

  new Document("$group", 
    new Document("_id", 
      new Document("machineID", "$machineID").append("errorID","$errorID")
    ).append("count", new Document("$sum",1))
  ),

  new Document("$project", 
    new Document("machineID", "$_id.machineID")
      .append("errorID", "$_id.errorID")
      .append("count", "$count")
      .append("_id", 0)
  )
));