$replaceRoot of embedded document inside an array in MongoDB

Question

I am fairly new to MongoDB and I came across the $replaceRoot(aggregation) which I need to output the document the way I need it.

Document Schema

{
name: "Apple",
image: "",
is_fruit: true,
other: [
  {
    url: "",
    quotes: { // saved as ObjectId and is then lookedup or populated
    text: "An apple a day keeps the doctor away"
  }
}
]
}

Wanted Output

{
  name: "Apple",
  image: "",
  is_fruit: true,
  other: [
    {
      text: "An apple a day keeps the doctor away"
    },
  ...
  ]
  }

i.e: To make quotes field as the root of the other array and not the root of entire document.

Thank you.

I don't really get what you're trying to achieve here. Are you trying to limit the number of returned fields inside the array? Or where do the ´url´ and ´quotes´ field go to? — dnickless
– dnickless, Commented Feb 15, 2018 at 13:25

s7vr · Accepted Answer · 2018-02-15 02:53:45Z

1

There is no $replaceRoot like for embedded array but you can achieve similar effect using $map to transform the array into new format.

Something like

db.col.aggregate([
  {
    "$addFields": {
      "other": {
        "$map": {
          "input": "$other",
          "as": "res",
          "in": {
            "text": "$$res.text"
          }
        }
      }
    }
  }
])

You can easily do something similar in client side code.

answered Feb 15, 2018 at 2:53

s7vr

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Comments

Viveka · Accepted Answer · 2019-12-05 08:57:39Z

0

By using $replaceRoot(aggregation) here is the output. P.S: The collection name I used is 'demoStack' replace it with your specific collections.

Query is :

db.demoStack.aggregate([
{ $replaceRoot: { newRoot: { $mergeObjects: [ 
    {name:"$name"},
    { image: "$image" },
    {is_fruit:"$is_fruit"},
    {other:"$other.quotes"}        
    ] } } } ])

edited Dec 5, 2019 at 8:57

answered Dec 5, 2019 at 8:50

Viveka

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