mongodb - MongoDB 统计多个字段

Question

这是输入集合：

{"itemName" : "A1", "voteType" : "up"}
{"itemName" : "A1", "voteType" : "up"}
{"itemName" : "A1", "voteType" : "down"}
{"itemName" : "A2", "voteType" : "up"}
{"itemName" : "A2", "voteType" : "down"}
{"itemName" : "A2", "voteType" : "down"}
{"itemName" : "A2", "voteType" : "down"}
and so on...

有谁知道如何通过聚合获得以下文件？

另外，我们如何使用 Spring Data 来实现呢？

{ "id" : "A1", "CountUp" : 2, "CountDown" : 1}
{ "id" : "A2", "CountUp" : 1, "CountDown" : 3}

Answer 1

这应该有效。运算符可$cond用于填充CountUp和CountDown字段。之后它只是对数据进行分组

     {
         $project:
           {
             itemName: 1,
             countUp:
               {
                 $cond: [ { $eq: [ "$voteType", "up" ] }, 1, 0 ]
               },
               countdown:
               {
                 $cond: [ { $eq: [ "$voteType", "down" ] }, 1, 0 ]
               }
           }
      },

     { $group : { _id : "$itemName", countUp: { $sum: "$countUp" }, countDown: { $sum: "$countdown" } }}