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mongodb - 如何通过多个本地字段比较对 mongoDB 集合进行链式聚合？

问题描述

这是我的收藏：

用户：

{
    user: xxx,
    job: xxx,
    order: xxxx
}

汽车：

{
    order: xxxx,
    cost: yyyy
}

飞机：

{
    order: xxxx,
    cost: yyyy
}

保险：

{
    cost: yyyy,
    terms: zzzz
}

首先，我想根据匹配“订单”字段的值将“用户”与“汽车”或“飞机”结合起来。之后，我将结果与基于“成本”字段的“保险”集合相结合。

所以，我希望结果是这样的：

{ "user" : xx, ..., "order": dsad, "cars": {}, "plane": {"order": ddsa, "cost": awew} , "terms": sdada},
{ "user" : yy, ..., "order": sawe, "cars": {"order": fda, "cost": qwez}, "plane": {} , "terms": tyrw},
{ "user" : zz, ..., "order": qwez, "cars": {}, "plane": {} , "terms":{} }

我尝试使用 db.users.aggregate() 和 $lookup 如下：

db.check.aggregate([
{
    $lookup:
        {
            from: "cars",
            localField: "order",
            foreignField: "order",
            as: "cars"
        }    
},
{
    $unwind: {path: "$cars", preserveNullAndEmptyArrays: true}
},    
{
    $lookup:
        {
            from: "planes",
            localField: "order",
            foreignField: "order",
            as: "planes"
        }    
},
{
    $unwind: {path: "$planes", preserveNullAndEmptyArrays: true}
},

结果是：

{ "user" : xx, ..., "order": dsad, "cars": {}, "plane": {"order": ddsa, "cost": awew}},
{ "user" : yy, ..., "order": sawe, "cars": {"order": fda, "cost": qwez}, "plane": {}},
{ "user" : zz, ..., "order": qwez, "cars": {}, "plane": {}}

但是，我不知道从那里走得更远！

标签： mongodbnosqlaggregate

解决方案

您可以将$lookup 与管道一起使用来获得所需的内容。

试试这个 ：

db.check.aggregate([
{
    $lookup:
        {
            from: "cars",
            localField: "order",
            foreignField: "order",
            as: "cars"
        }    
},
{
    $unwind: {path: "$cars", preserveNullAndEmptyArrays: true}
},    
{
    $lookup:
        {
            from: "planes",
            localField: "order",
            foreignField: "order",
            as: "planes"
        }    
},
{
    $unwind: {path: "$planes", preserveNullAndEmptyArrays: true}
},{
    $lookup:{
        from : "insurance",
        let  : {
            carCost : "$cars.cost",
            planeCost : "$planes.cost"
        },
        pipeline : [{
            $match : {
                $expr :{
                    $or : [{
                        cost : "$$carCost" 
                    },{
                        cost : "$$planeCost"
                    }
                    ]
                }
            }
        }],
        as : "insurance"
    }
},{
    $unwind: {path: "$insurance", preserveNullAndEmptyArrays: true}
},{
    $project : {
        user:1,
        order:1,
        cars:1,
        planes:1,
        terms : "$insurance.terms"
    }
}]

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