MongoDB:检查对象数组，如果存在返回true，否则为false

Question

我正在尝试查询集合中的数组，并在数组中存在对象时投影值"true“。如果该对象不存在于数组中，则项目"false“。我在MongoDB工作，我对它不太熟悉。

在我的场景中，我有两个正在使用的集合。我正在聚合一组‘员工’成员，我正在执行一个$lookup功能到一个‘业务’集合。在“业务”中，我拥有一系列业务功能。

例如，我收集了工作人员

staff = [
  ...
  {_id: 1, businessId: 11},
  {_id: 2, businessId: 22},
  ....
]

企业征集

businesses = [
  ...
  {_id: 11, capabilities: ["claiming", "pushing"]},
  {_id: 22, capabilities: ["claiming", "popping"]},
  ....
]

并设置如下所示的$lookup

db.getCollection('staff').aggregate([
    {
        $lookup:
            {
                from: "businesses",
                localField: "businessId",
                foreignField: "_id",
                as: "business_Info"
            }
    },

如果“$project”出现在“功能”中，那么我如何才能使每个工作人员的$canClaim: true这样的值出现呢？

Answer 1

可以使用$in聚合运算符检查数组是否包含该值。

db.getCollection("staff").aggregate([
  { "$lookup": {
    "from": "businesses",
    "localField": "businessId",
    "foreignField": "_id",
    "as": "business_Info"
  }},
  { "$unwind": "$business_Info" },
  { "$addFields": {
    "canClaim": { "$in": ["claiming", "$business_Info.capabilities"] }
  }}
])

MongoPlayground

Answer 2

db.getCollection("staff").aggregate(

    // Pipeline
    [
        // Stage 1
        {
            $lookup: // Equality Match
            {
                from: "businesses",
                localField: "businessId",
                foreignField: "_id",
                as: "businessInfo"
            }

            // Uncorrelated Subqueries
            // (supported as of MongoDB 3.6)
            // {
            //    from: "<collection to join>",
            //    let: { <var_1>: <expression>, …, <var_n>: <expression> },
            //    pipeline: [ <pipeline to execute on the collection to join> ],
            //    as: "<output array field>"
            // }
        },

        // Stage 2
        {
            $project: {
                businessId: 1,
                businessInfo: {
                    $arrayElemAt: ['$businessInfo', 0]
                }
            }
        },

        // Stage 3
        {
            $addFields: {
                "businessInfo.canClaim": {
                    $cond: {
                        if: {
                            $gte: [{
                                $indexOfArray: ["$businessInfo.capabilities", 'claiming']
                            }, 0]
                        },
                        then: true,
                        else: false
                    }
                }
            }
        },

    ]



);