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Filter on a mongodb keys in aggregation

I have a document like below

{
  "name" :{
  "English": "AA",
  "Bengali": "BB",
  "Gujarati": "CC",
  "Hindi": "DD"} 
}

can I filter it based on the keys e.g. need to filter only on ‘English’ and ‘Hindi’ so the output should be

{
  "name" :{
  "English": "AA",
  "Hindi": "DD"} 
}
Tags:

2

Answers


  1. 0

    One way to do this is to first turn the object into an array of key-value pairs [{ "k": "Bengali", "v": "BB" }, { "k": "English", "v": "AA" }...] using $objectToArray

    Then call $filter on the array and take only the ones you need

    Finally, convert that array back to an object using $arrayToObject

    db.collection.aggregate([
  {
    $project: {
      name: {
        $arrayToObject: {
          $filter: {
            input: { $objectToArray: "$name" },
            cond: { $in: [ "$$this.k", [ "English", "Hindi" ] ] }
          }
        }
      }
    }
  }
])

    playground

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  2. 0

    The simple option is to check for key existence and project only the necessary keys :

    db.collection.find({
"$and": [
 {
   "name.Hindi": {
     "$exists": true
   }
  },
  {
   "name.English": {
     "$exists": true
   }
 }
]
},
{
name: {
 "English": 1,
 "Hindi": 1
 }
})

    Playground

    But the better option if you are going to use this filter often is to modify the keys to values as follow:

    [
  {
  "_id": ObjectId("5a934e000102030405000000"),
   "name": [
    {key:"Bengali" , value:"BB"},
    {key:"English" , value:"AA"},
    {key:"Gujarati", value:"CC"},
    {key:"Hindi",  value:"DD" }
  ]
 }
]

    where you can do something faster like:

       db.collection.find({
  "name.key": {
  $in: [
  "English",
  "Hindi"
  ]
  }
 },
 {
 name: {
  $filter: {
  input: "$name",
  as: "item",
  cond: {
    $in: [
      "$$item.key",
      [
        "English",
        "Hindi"
       ]
      ]
     }
   }
  }
 })

    Assuming you create in advance an index on the "name.key" field.

    playground

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