设置差异给出不正确的结果

Question

我们正在尝试打印 2 个数组的差异，从不同的集合中检索为 below.However，setdifference 似乎不起作用。
可能有什么问题？
预期输出：

{ "request" : [{ "requestId" : "REQ4" }], "unsent" : ["1234"] }

代码摘录和阶段输出如下：

AggregateIterable<Document> diff = 
                    scrips.aggregate(Arrays.asList(
                        Aggregates.group(null, Accumulators.addToSet("global", "$scrip"))
                    ,Aggregates.lookup("requests",new ArrayList<Bson>(Arrays.asList(new Document(
                            Document.parse("{\"$match\": { \"requestId\":'" + reqparam + "'}}")))),"request")

[此处输出：{ "_id" : null, "global" : ["3553", "5647", "0001"], "request" : [{ "_id" : { " $oid" : "5d6e37db1886a24e70b88b42" }, "requestId" : "REQ4", "scrips" : ["3553", "5647", "1234"] }] }]

        ,Aggregates.project(
                    Projections.fields(
                    Projections.excludeId(),
                    Projections.computed("unsent", 
                            Document.parse("{ $setDifference: [\"$request.scrips\", \"$global\"] }"))
                )
            )

[此处输出：{ "request" : [{ "requestId" : "REQ4" }], "unsent" : [["3553", "5647", "1234 "]] }]

Answer 1

这里的问题是您在使用未被访问的 setDifference 时尝试访问数组中的字段，而只是按原样返回全局脚本，请尝试在 setdifference

中添加 arrayelemat

 {
    $project: {
      unsent: {
        $setDifference: [
          {
            $arrayElemAt: [
              "$request.scrips",
              0
            ]
          },
          "$global"
        ]
      }
    }
  }

给出输出：

[
  {
    "_id": null,
    "scrips": [
      "1234"
    ]
  }
]