如何在 mongodb 中应用 $lookup 条件？

Posted 2023-03-11

【中文标题】如何在 mongodb 中应用 $lookup 条件？

【英文标题】：How to apply $lookup with conditions in mongodb?

【发布时间】：2020-05-11 04:37:15

【问题描述】：

我正在使用 mongodb 数据库并希望在 2 collections 上应用 $lookup 但有特定条件。 我有一个collection 像这样命名为Company

new Schema(
    name: String,
    benefit: String,
    benefitDesc: String,
    company_url: String,
    logoUrl: String,
    coverUrl: String,
    desc: String,
    createdAt: String,
    categoryId:  type: Schema.Types.ObjectId, ref: 'categories' ,
)

另一个collection 像这样命名为Referrallinks

new Schema(
    referral_link: String,
    referral_code: String,
    isLink: Number,
    offer_name: String,
    offer_desc: String,
    user_email: String,
    companyId:  type: Schema.Types.ObjectId, ref: 'companies' ,
    addedByAdmin:  type: Boolean, default: true ,
    number_of_clicks: Number,
    referral_country: String,
    link_status: String,
    categoryId:  type: Schema.Types.ObjectId, ref: 'categories' ,
    number_of_clicks:  type: Number, default: 0 ,
    createdAt: String,
    updatedAt: String,
    userId:  type: Schema.Types.ObjectId, ref: 'users' 
)

现在当我应用这个$lookup

Company.aggregate([
    $lookup: 
        from: 'referrallinks',
        localField: '_id',
        foreignField: 'companyId',
        as: 'referrals'
    
])

所以我让所有referrals 的公司都像array 这样

[
  name : '', benefit : '', benefiDesc : '', referrals : [],
  name : '', benefit : '', benefiDesc : '', referrals : [],
  name : '', benefit : '', benefiDesc : '', referrals : [],
  .....
]

但我希望每个 company's referrals 数组中只有具有 link_status 值 Approved 的推荐。

**注意：**我也想拥有 category 和 company 的对象并尝试了这种聚合，但它给出了错误

  from: "referrallinks",
  let:  company_id: "$_id" ,
  pipeline: [
    $match: 
      $expr: 
       $and: [
         $eq: [ "$$company_id", "$companyId" ] ,
         $eq: [ "$link_status", "Approved" ] 
       ]
     
    ,
  
    $lookup : 
    from : "categories",
    let  : "category_id" : "$categoryId",
    pipeline : [
      
        $match : 
          $expr : 
            $eq : ["category_id","$_id"]
          
        
      
    ],
    as : "company"
   
  
 ],
 as: "referrals"

我怎样才能做到这一点？

【参考方案1】：

使用$lookup with custom pipeline指定附加过滤条件：

Company.aggregate([
    $lookup: 
        from: "referrallinks",
        let:  company_id: "$_id" ,
        pipeline: [
            $match: 
                $expr: 
                    $and: [
                         $eq: [ "$$company_id", "$companyId" ] ,
                         $eq: [ "$link_status", "Approved" ] 
                    ]
                
            
        ],
        as: "referrals"
    
])

编辑：要运行嵌套的$lookup，您的代码应如下所示：

Company.aggregate([
    $lookup: 
        from: "referrallinks",
        let:  company_id: "$_id" ,
        pipeline: [
            
                $match: 
                    $expr: 
                        $and: [
                             $eq: [ "$$company_id", "$companyId" ] ,
                             $eq: [ "$link_status", "Approved" ] 
                        ]
                    
                
            ,
            
                $lookup: 
                    from: "categories",
                    localField: "categoryId",
                    foreignField: "_id",
                    as: "company"
                
            
        ],
        as: "referrals"
    
])

【讨论】：

您的查询中有一些错误。在此处查看错误imgur.com/6tRCUuv

@ahsan 啊是的，$expr 丢失，请重试

我可以同时拥有populate 和$lookup 吗？就像我有companyId 作为category 集合的（ObjectId），我想在我的结果中也有category。

@ahsan 在这种情况下你必须继续使用$lookup

我试过了，但运气不好。你能修改你的答案吗？