Question 228169 in Mongodb Question posted in
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How to use $cond in mongoDB

Please refer the attached image and help me explain this case.
Why didn’t cova_items column assigned value of InStock column when woo_order_id is null?
query command:

db.cova_order.aggregate([
    {
        $project:{
            InStock:1,
            woo_order_id:1,
            woo_order_data:1,
            cova_items:{
                    $cond: { if: { $eq:["$woo_order_id",null] }, then:"$InStock" , else:"$woo_order_data" }
            }
        }
    },

enter image description here

=> Result: cova_items column shows value like as woo_order_data column

Please show me the mistake if having. Thanks

Tags:

2

Answers


  1. 0

    $cond has simplified syntax.

    { $cond: [ <boolean-expression>, <true-case>, <false-case> ] }

    Fast solution:

    Seems your $woo_order_id is not null, but empty.

    {$cond:[ {$eq:["$woo_order_id", ""] }, "$InStock", "$woo_order_data"]}

    Complete solutuion

    Whether $woo_order_id can be null, undefined or missing, with the $ifNull operator we cover them all.

    db.cova_order.aggregate([
  {
    $project: {
      InStock: 1,
      woo_order_id: 1,
      woo_order_data: 1,
      cova_items: {
        $cond: [
          { $eq: [ { "$ifNull": [ "$woo_order_id", ""] }, "" ] },
          "$InStock",
          "$woo_order_data"
        ]
      }
    }
  }
])

    MongoPlayground

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  2. 0

    Given Data:


    Task : If woo_order_id is null or "" (empty string) then return Instock and if it is not null/empty string then return woo_order_data

    [
  {
    "InStock": 1,
    "woo_order_id": null,
    "woo_order_data": "1d",
    
  },
  {
    "InStock": 2,
    "woo_order_id": 2,
    "woo_order_data": "2d",
    
  },
  {
    "InStock": 3,
    "woo_order_id": 3,
    "woo_order_data": "3d",
    
  },
  {
    "InStock": 4,
    "woo_order_id": "",
    "woo_order_data": "4d",
    
  }
]

    Solution:

    db.collection.aggregate([
  {
    $project: {
      InStock: 1,
      woo_order_id: 1,
      woo_order_data: 1,
      cova_items: {
        $cond: {
          if: {
            "$or": [
              {
                "$eq": [
                  "$woo_order_id",
                  ""
                ]
              },
              {
                "$eq": [
                  "$woo_order_id",
                  null
                ]
              }
            ]
          },
          then: "$InStock",
          else: "$woo_order_data"
        }
      }
    }
  }
])

    Output :

    [
  {
    "InStock": 1,
    "_id": ObjectId("5a934e000102030405000000"),
    "cova_items": 1,
    "woo_order_data": "1d",
    "woo_order_id": null
  },
  {
    "InStock": 2,
    "_id": ObjectId("5a934e000102030405000001"),
    "cova_items": "2d",
    "woo_order_data": "2d",
    "woo_order_id": 2
  },
  {
    "InStock": 3,
    "_id": ObjectId("5a934e000102030405000002"),
    "cova_items": "3d",
    "woo_order_data": "3d",
    "woo_order_id": 3
  },
  {
    "InStock": 4,
    "_id": ObjectId("5a934e000102030405000003"),
    "cova_items": 4,
    "woo_order_data": "4d",
    "woo_order_id": ""
  }
]
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