mongodb - 当父元素在每条记录中具有不同名称时，选择 mongodb 集合中的子元素

Question

我的 mongodb 集合有以下 json 格式，其中我需要选择子元素来执行计算，但父元素每条记录中都有不同的名称。

distribution is the parent element and 5d39e82f9ab1 and 5d09f133 are the variable child elements in each record.

{"distribution" : {
        "5d39e82f9ab1" : {
            "id" : "5cfa18a", 
            "name" : "Test1", 
            "feeTarget" : "5d39e82", 
            "onBoardAgent" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "transAgent" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "redeemAgent" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "merchant" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "system" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "aggregator" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "distributor" : {
                "debit" : 0, 
                "credit" : 0
            }
        }
    }
}


{"distribution" : {
        "5d09f133" : {
            "id" : "5d09f133", 
            "name" : "test2", 
            "feeTarget" : "5d09f133", 
            "onBoardAgent" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "transAgent" : {
                "debit" : 0, 
                "credit" : 28
            }, 
            "redeemAgent" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "merchant" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "system" : {
                "debit" : 0, 
                "credit" : 7
            }, 
            "aggregator" : {
                "debit" : 0, 
                "credit" : 0
            }, 
            "distributor" : {
                "debit" : 0, 
                "credit" : 0
            }
        }
    }
}

我想选择并执行如下操作:

以下是可能的查询:

"$project" : {
                "distribution.*.onBoardAgent" : 1,
                Difference: { $subtract: [ "$distribution.*.onBoardAgent.debit", $distribution.*.onBoardAgent.debit" ] }
            }
        }, 

这里“*”是我每个集合中的变量名称。

Answer 1

MongoDB 中没有 "*" 语法。要动态遍历 BSON 文档，您需要使用 $objectToArray和 $arrayToObject运营商。第一个运算符返回一个键值对数组，因此您必须使用 $map转换您的嵌套对象

db.collection.aggregate([
    {
        $addFields: {
            distribution: {
                $arrayToObject: {
                    $map: {
                        input: { $objectToArray: "$distribution" },
                        as: "dist",
                        in: {
                            k: "$$dist.k",
                            v: {
                                onBoardAgent: "$$dist.v.onBoardAgent",
                                difference: { $subtract: [ "$$dist.v.onBoardAgent.debit", "$$dist.v.onBoardAgent.credit" ] }
                            }
                        }
                    }
                }
            }
        }
    }
])

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