比较对象数组中数组的大小

Question

我想find所有sCompetitions.length大于competitions.length的文档。

以下是一些示例文档文档：

{
    "_id" : ObjectId("59b28f432b4353d3f311dd1b"),
    "name" : "Ford Focus RS 2008",
    "requirements" : [ 
        {
            "rankType" : "D1",
            "competitions" : [ 
                ObjectId("59b151fd2b4353d3f3116827"), 
                ObjectId("59b151fd2b4353d3f3116829")
            ],
            "sCompetitions" : [ 
                "Rallye Monte-Carlo", 
                "Rally Sweden"
            ]
        }, 
        {
            "rankType" : "A3",
            "competitions" : [
                ObjectId("59b151fd2b4353d3f3116f6b")
            ],
            "sCompetitions" : [ 
                "Rally Italia Sardegna", 
                "Neste Rally Finland"
            ]
        }
    ]
},
{
    "_id" : ObjectId("0000b28f432b4353f311dd1b"),
    "name" : "Ford Focus RS 2012",
    "requirements" : [ 
        {
            "rankType" : "D1",
            "competitions" : [ 
                ObjectId("59b151fd2b4353d3f3116827"), 
                ObjectId("59b151fd2b4353d3f3116829")
            ],
            "sCompetitions" : [ 
                "Rallye Monte-Carlo", 
                "Rally Sweden"
            ]
        }, 
        {
            "rankType" : "A3",
            "competitions" : [
                ObjectId("59b151fd2b4353d3f3116f6b"),
                ObjectId("59b151fd2b4353d3f3116f6b")
            ],
            "sCompetitions" : [ 
                "Rally Italia Sardegna", 
                "Neste Rally Finland"
            ]
        }
    ]
}

所以看一下样本，它只会返回ObjectId("59b28f432b4353d3f311dd1b")

我的问题是requirements本身就是一个数组，所以我需要以某种方式迭代它。

Answer 1

不需要“迭代”。您真正需要的是在从$anyElementTrue返回结果之后进行$map检查。您可以在$redact操作中完成所有这些操作：

Model.aggregate([
  { "$redact": {
    "$cond": {
      "if": {
        "$anyElementTrue": {
          "$map": {
            "input": "$requirements",
            "as": "r",
            "in": { 
              "$gt": [
                { "$size": "$$r.sCompetitions" },
                { "$size": "$$r.competitions" }
              ]
            }
          }
        }
      },
      "then": "$$KEEP",
      "else": "$$PRUNE"
    }
  }}
])

因此，这是$size对每个数组元素的简单比较，如果其中“任何”元素是true，则文档将从结果中“保存”或“修剪”。