How do I create a single array of object from nested array of obejcts mongodb aggregate?

Question

I am new to Mongodb and don't know much about aggregates how do I change below object to desired single array of object.

[
  {
    id: "1",
    title: "First Title",
    des: "This is desc",
    contents: [
      {
        id: "1",
        title: "content-1 title",
        des: "This is desc"
      },
      {
        id: "2",
        title: "Content-2 title",
        des: "This is desc"
      }
    ]
  },
  {
    id: "2",
    title: "Second Title is Here",
    des: "This is desc",
    contents: [
      {
        id: "1",
        title: "content-1 title",
        des: "This is desc"
      },
      {
        id: "2",
        title: "Content-2 title",
        des: "This is desc"
      }
    ]
  }
]

My Desired Out Single array :

[
  {
    id: "1",
    title: "First Title",
    des: "This is desc"
  },
  {
    id: "1",
    title: "content-1 title",
    des: "This is desc"
  },
  {
    id: "2",
    title: "Content-2 title",
    des: "This is desc"
  },
  {
    id: "2",
    title: "Second Title is Here",
    des: "This is desc"
  },
  {
    id: "1",
    title: "content-1 title",
    des: "This is desc"
  },
  {
    id: "2",
    title: "Content-2 title",
    des: "This is desc"
  }
]

YuTing · Accepted Answer · 2022-04-07 06:06:34Z

1

db.collection.aggregate([
  {
    $set: {
      contents: {
        $concatArrays: [
          [
            {
              id: "$id",
              title: "$title",
              des: "$des"
            }
          ],
          "$contents"
        ]
      }
    }
  },
  {
    $unwind: "$contents"
  },
  {
    $replaceWith: "$contents"
  }
])

mongoplayground

edited Apr 7, 2022 at 6:06

answered Apr 7, 2022 at 5:02

YuTing

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4 Comments

Rammehar Sharma Over a year ago

Wow Great Answer. But still have some issue, all contents should be shown below main object. order is changed in result. also need to sort according to top one id

YuTing Over a year ago

I update my answer to solve the problem of order changing. If you want to have only one object instead of six, you can group them all. Add $sort stage after $unwind` stage can sort documents.

Rammehar Sharma Over a year ago

mongoplayground link now did't work

YuTing Over a year ago

@RammeharSharma ok I fix it

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