如何在管道聚合(mongoDB)中比较文档中的两个字段 [英] how to compare two fields in a document in pipeline aggregation (mongoDB)

问题描述

我有一个如下文件:

{
  "user_id": NumberLong(1),
  "updated_at": ISODate("2016-11-17T09:35:56.200Z"),
  "created_at": ISODate("2016-11-17T09:35:07.981Z"),
  "banners": {
    "normal_x970h90": "/images/banners/4/582d79cb3aef567d64621be9/photo-1440700265116-fe3f91810d72.jpg",
    "normal_x468h60": "/images/banners/4/582d79cb3aef567d64621be9/photo-1433354359170-23a4ae7338c6.jpg",
    "normal_x120h600": "/images/banners/4/582d79cb3aef567d64621be9/photo-1452570053594-1b985d6ea890.jpg"
  },
  "name": "jghjghjghj",
  "budget": "2000",
  "plan": null,
  "daily_budget": "232323",
  "daily_budget_auto": "",
  "href": "qls2.ir",
  "targets": {
    "cats": [
      "fun",
      "news"
    ],
    "region": "inIran",
    "iran_states": null,
    "os": "all",
    "gold_network": true,
    "dont_show_between_1_n_8": true
  },
  "payment": {
    "bank": "mellat",
    "tax": "add"
  },
  "click_cost": "102000",
  "status": null
}

在检查查询中的其他一些参数时，我想检查budget是否低于click_cost:

I want to check if budget is lower than click_cost while I'm checking some other parameters in my query :

db.bcamp.aggregate(
    [
        {
            $match:{
                $and: [ 
                    {"targets.cats":{
                        "$in" : ["all"]
                        }
                    },

                    {"banners.normal_x970h90":{
                        "$exists":true
                        }
                    },

                    {"href": {
                        $nin: ["qls.ir"]
                        }
                    }
                ]
            }
        }
    ]).pretty();

我尝试过比较方法:

db.bcamp.aggregate(
    [
        {$project: {ab: {$cmp: ['$budget','$clickcost']}}},
        {$match: {ab:{$gt:1}}}
    ]).pretty();

但是我得到的结果是错误的，它总是返回4个文档，它们的预算可能比click_cost更好，这意味着它获取了错误的数据.

But I was getting wrong result, it returns always 4 document which their budget may or may not be grater than click_cost, which it means it fetch wrong data.

如何将该比较添加到我的mongoDB管道中?

How can I add that comparison to my mongoDB pipeline?

推荐答案

问题不在于比较运算符，它是您要比较的值的类型.您应该将变量的类型更改为Numbers.根据您的比较将匹配项更改为1，-1或0.

The problem is not with comparison operator, its the type of value you are comparing. You should change types of variable to Numbers. Change your match to 1, -1 or 0 based on your comparison.

db.bcamp.aggregate(
[
  {$project: {ab: {$cmp: ['$budget','$clickcost']}}},
  {$match: {ab:{$eq:1}}}
]).pretty();

您可以在3.6版本中使用$expr.

You can use $expr in 3.6 version.

db.bcamp.aggregate(
[
  {$match: {$expr: {$eq: ["$budget", "$clickcost"]}}}
]).pretty();

或

db.bcamp.find(
 {$expr: {$eq: ["$budget", "$clickcost"]}}
).pretty();

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