how to compare two fields in a document in pipeline aggregation (mongoDB)

问题

I have a document like below :

{
  "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
}

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();

I have tried compare method like :

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

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.

How can I add that comparison to my mongoDB pipeline?

回答1:

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();

You can use $expr in 3.6 version.

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

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

来源：https://stackoverflow.com/questions/41377775/how-to-compare-two-fields-in-a-document-in-pipeline-aggregation-mongodb

标签

mongodb

comparison

aggregation-framework

document

pipeline