Extract value of array and add in the same select mongoDB

Question

I am new to the mongoDB aggregation and I have this situation. I have this Json and I need to convert by "select" this object:

{
    "type": "PF",
    "code": 12345
    "Name": Darth Vader,
    "currency": "BRL",
    "status": "SINGLE",
    "adress": [
        {
            "localization": "DEATH STAR",
            "createDate": 1627990848665
        },
        {
            "localization": "TATOOINE",
            "createDate": 1627990555665
        },
    ]
}

this way:

{
    "type": "PF",
    "code": 12345
    "Name": Darth Vader,
    "currency": "BRL",
    "status": "SINGLE",
    "localization": "DEATH STAR",
    "createDate": 1627990848665
},
{
    "type": "PF",
    "code": 12345
    "Name": Darth Vader,
    "currency": "BRL",
    "status": "SINGLE",
    "localization": "TATOOINE",
    "createDate": 1627990555665
}

So, after my query is complete, I will have 02 objects instead of 01. How can I do this? I would like to do this via select because after converting I will sort by createDate and limit the number of records to return to the API. I'm using Criteria em my project.

Does this answer your question? Retrieve only the queried element in an object array in MongoDB collection — ℛɑƒæĿᴿᴹᴿ
– ℛɑƒæĿᴿᴹᴿ, Commented Aug 31, 2021 at 20:17
Unfortunately no because I need to repeat the same informations of the first element to others. =( — Patrick Teixeira
– Patrick Teixeira, Commented Aug 31, 2021 at 20:35
Please provide enough code so others can better understand or reproduce the problem. — Community
– Community Bot, Commented Sep 3, 2021 at 14:15

Takis · Accepted Answer · 2021-09-01 13:57:54Z

2

The way to do this is $unwind, this will make 1 copy of the document, for each member of the array.

Test code here

db.collection.aggregate([
  {
    "$unwind": {
      "path": "$user.adress"
    }
  },
  {
    "$set": {
      "user": {
        "$mergeObjects": [
          "$user",
          "$user.adress"
        ]
      }
    }
  },
  {
    "$unset": [
      "user.adress"
    ]
  },
  {
    "$sort": {
      "createDate": 1
    }
  },
  {
    "$limit": 10
  }
])

Edit1 (the above is if user is a field, if it was the name of the collection)

$$ROOT is a system variable that has as value all the document

Test code here

Query

db.collection.aggregate([
  {
    "$unwind": {
      "path": "$adress"
    }
  },
  {
    "$replaceRoot": {
      "newRoot": {
        "$mergeObjects": [
          "$$ROOT",
          "$adress"
        ]
      }
    }
  },
  {
    "$unset": [
      "adress"
    ]
  },
  {
    "$sort": {
      "createDate": 1
    }
  },
  {
    "$limit": 10
  }
])

edited Sep 1, 2021 at 13:57

answered Aug 31, 2021 at 20:45

Takis

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9 Comments

Patrick Teixeira Over a year ago

I have just a only question. I'm looking in my json and I made a mistake... I dont have the name USER. How can I do in this situation? Only this way... { "type": "PF", "code": 12345 "Name": Darth Vader, "currency": "BRL", "status": "SINGLE", "adress": [ { "localization": "DEATH STAR", "createDate": 1627990848665 }, { "localization": "TATOOINE", "createDate": 1627990555665 }, ] }

Takis Over a year ago

i was wondering a bit, if user was a field or the name of the collection, try the edit, i think you will be fine.

Patrick Teixeira Over a year ago

Yes... That's exactly what I needed! Thank you so much (AGAIN)!! =)

Patrick Teixeira Over a year ago

I remember about another situation... I have the actual location in the Json and I need to keep the actual location and reply the other informations for the "children" as you show me. How I keep the actual location in this case and add the "children" for the return..???? mongoplayground.net/p/W4hBM0KN1UD mongoplayground.net/p/W4hBM0KN1UD

Takis Over a year ago

i am confused a bit, if its different question maybe ask new one, with new data and the expected output you want. so people can help.

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