MongoDB- How to $project items from an object?-CodePudding

Playground https://mongoplayground.net/p/tIMLOtWTnno

DATA:

[

  {
    "_id": "1",
    "data": {                     // How to remove this "data" Field
      "colour": "Blue",
      "size": "12",
    }
  },
  {
    "_id": "2",
    "data": {                     // How to remove this "data" Field
      "colour": "Silver",
      "size": "20",
    }
  }

]

I want to remove the data field.

Expected Output:

[
  {
    "_id": "1",
    "colour": "Blue",
    "size": "12",
    
  },
  {
    "_id": "2",
    "colour": "Silver",
    "size": "20",
    
  }
]

Tried it like this:

db.collection.aggregate({
  $project: {
    _id: 1,
    data: {
      $objectToArray: "$data"
    }
  },
  
},
{
  $unwind: "$data"
},
{
  $project: {
    "$data.k": "$data.v"
  }
})

How to do this ?

CodePudding user response：

Query1

set to add the fields in the root and remove the data

*you could use also project

Test code here

aggregate(
[{"$set":
  {"colour":"$data.colour",
   "size":"$data.size",
   "data":"$$REMOVE"}}])

Query2

more general solution without the need to type each field in project
merge the data embeded object with the root, and make it new root
remove the data field

Test code here

aggregate(
[{"$replaceRoot":{"newRoot":{"$mergeObjects":["$data", "$$ROOT"]}}},
 {"$project":{"data":0}}])