Mongodb - arrayMerge specific fields

Question

How can i use merge array to a new array from a detail document there is an example of data

Example of result detail

[{
    country: 'USA',
    val: 500,
    items: [
        {val:50, ...manyFieldsToIgnore},
        {val:30, ...manyFieldsToIgnore},
        {val:110, ...manyFieldsToIgnore},
    ]
}];

Output expected

{ items:[ 
    {
        country: 'USA',
        newNameValue: 500,
    },
    {
        country: 'USA',
        newNameValue: 50,
    },
    {
        country: 'USA',
        newNameValue: 30,
    },
    {
        country: 'USA',
        newNameValue: 110,
    },
};

im try to use $project and $concatArrays but i dont know how to set the new field(country) in details and change their key names

$project: {
    'root.country': '$country',
    items: concatArrays[ '$items'],
},
$project: {
    payments: concatArrays[ '$items', ['$root'] ],
}

prasad_ · Accepted Answer · 2020-10-15 06:45:19Z

2

The following aggregation returns the desired result. Note the usage of the Aggregation Array Operators - $map and $concatArrays:

db.test.aggregate([
  { 
      $addFields: {
          items: { 
             $map: { 
                 input: "$items", 
                 in: { country: "$country", newNameVal: "$$this.val"  } 
             }
          }
      }
  },
  { 
      $project: { 
          items: { 
              $concatArrays: [ [ { country: "$country", newNameVal: "$val" } ],  "$items" ]
          } 
      }
  }
])

answered Oct 15, 2020 at 6:45

prasad_

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turivishal · Accepted Answer · 2020-10-15 05:09:49Z

1

You can try,

$addFields to add country in items array
$project to concat 2 arrays one is outer val and country and second is items array using $concatArrays

db.collection.aggregate([
  { $addFields: { "items.country": "$country" } },
  {
    $project: {
      items: {
        $concatArrays: [
          [
            {
              val: "$val",
              country: "$country"
            }
          ],
          "$items"
        ]
      }
    }
  }
])

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answered Oct 15, 2020 at 5:09

turivishal

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