Return dynamic values while project stage in mongo aggregation

July 7, 2022

I wanted to structure my response object while project stage of aggregation. But I am facing problem to concat a string with another key value.
Here is my aggregation return object

[
  {
    "total_price": 8.92,
    "paymentStatus": "Paid",
    "refundedAmount": 5
  },
  {
    "total_price": 20.92,
    "paymentStatus": "Paid",
    "refundedAmount": 15
  }
]

But I want to return as a structure of

[
  {
    "total_price": 8.92,
    "paymentStatus": "Paid",
    "refundedAmount": 5,
    "description": "Refunded 5"
  },
  {
    "total_price": 20.92,
    "paymentStatus": "Paid",
    "refundedAmount": 15,
    "description": "Refunded 15"
  }
]

Here totalPrice, paymentStatus and refundedAmount are available in database.
I want to add a key called description while project.

>Solution :

You need $concat operator and convert refundedAmount to string.

db.collection.aggregate([
  {
    "$project": {
      total_price: 1,
      paymentStatus: 1,
      refundedAmount: 1,
      description: {
        $concat: [
          "Refunded ",
          {
            $toString: "$refundedAmount"
          }
        ]
      }
    }
  }
])

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