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$$ mongodb

Liubomyr Siusar answered on October 5, 2022 Popularity 6/10 Helpfulness 1/10

answer $$ mongodb

$$ mongodb

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// $ is referred to the root document fields where as 
// $$ referred to the variable names.
[
  {
    data: [8,2,3,4]
  },{
    data: [6,3,7]
  },{
    data: [3,6,1,8,3,7]
  }
]

{
  "$map": {
    "input": "$data",
    "as": "currentData",
    "in": { "$size": "$$currentData" }
  }
}


// Here '$data' is the document array field and the $$currentData 
// is the variable taken in the as expression of $map aggregation.
// so, $$currentData -> each element from array $data


// Another example:
db.sales.aggregate( [
   {
      $project: {
         finalTotal: {
            $let: {
               vars: {
                  total: { $add: [ '$price', '$tax' ] },
                  discounted: { $cond: { if: '$applyDiscount', then: 0.9, else: 1 } }
               },
               in: { $multiply: [ "$$total", "$$discounted" ] }
            }
         }
      }
   }
] )

// Result
{ "_id" : 1, "finalTotal" : 9.450000000000001 }
{ "_id" : 2, "finalTotal" : 10.25 }

Popularity 6/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: javascript mongodb

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Contributed on Oct 05 2022

Liubomyr Siusar

0 Answers Avg Quality 2/10

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