Question 117196 in Mongodb Question posted in
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How to flatten a nested object in MongoDB?

I have a document of the form:

{
  "employee_addr": {
    "city": "London",
    "street": "Downing Street",
    "apartment": 10
  }

  "age": 58,
  "name": "Boris"
}

I want to flatten the document. That is, removing the employee_addr nested object and moving its properties to the root of the document.

This document is the result of an aggregation pipeline and I need to add another step to it

How can I do it?

Thanks!

Tags:

2

Answers


  1. 0

    One option is using $set if you have only several fields to flatten or you want to flatten an object but not necessarily down to the root:

    db.collection.aggregate([
  {
    $set: {
      city: "$employee_addr.city",
      street: "$employee_addr.street",
      apartment: "$employee_addr.apartment",
      employee_addr: "$$REMOVE"
    }
  }
])

    See how it works on the playground example.

    Oterwise, use @YongShun answer, which I was about to write, but @YongShun beat me to it 🙂

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  2. 0

    1. $replaceRoot – Replace the input document with new document.

      1.1. $mergeObjects – Merge ROOT document with employee_addr object.

    2. $unset – Remove employee_addr field.

    db.collection.aggregate([
  {
    $replaceRoot: {
      newRoot: {
        $mergeObjects: [
          "$$ROOT",
          "$employee_addr"
        ]
      }
    }
  },
  {
    $unset: "employee_addr"
  }
])

    Sample Mongo Playground

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