how to select all values of particular key from an array of objects

Question

Below is the collection in MongoDB by the name- "auto_sales" and I want to select all the values of "sales" from data which is an array of object.

Collection-
{
"name" : "auto_sales", 
"data" : [ 
{ "sales" : 10, 
  "temp" : 50 }, 

{ "sales" : 9, 
"temp" : 51 }, 

{"sales" : 8, 
"temp" : 55 }, 

{"sales" : 57, 
"temp" : 7 }, 

{"sales" : 58, 
"temp" : 8 } 
] }

Is there any query to get all the values of "sales" from "data".

Wernfried Domscheit · Accepted Answer · 2020-02-25 20:37:36Z

1

Do you mean this one:

db.collection.find(
   {},
   { "data.sales": 1 }
)

gives

{ 
    "_id" : ObjectId("5e55400d22139e9b31aa786e"), 
    "data" : [
        {
            "sales" : 10.0
        }, 
        {
            "sales" : 9.0
        }, 
        {
            "sales" : 8.0
        }, 
        {
            "sales" : 57.0
        }, 
        {
            "sales" : 58.0
        }
    ]
}

Or rather this one:

db.collection.aggregate([
   {
      $project: {
         sales: {
            $reduce: {
               input: "$data",
               initialValue: [],
               in: { $concatArrays: ["$$value", ["$$this.sales"]] }
            }
         }
      }
   }
])

or

db.collection.aggregate([
  {
    $project: {
      sales: {
        $map: {
          input: "$data",
          in: "$$this.sales"
        }
      }
    }
  }
])

gives

{ 
    "_id" : ObjectId("5e55400d22139e9b31aa786e"), 
    "sales" : [
        10.0, 
        9.0, 
        8.0, 
        57.0, 
        58.0
    ]
}

edited Feb 25, 2020 at 20:37

answered Feb 25, 2020 at 15:42

Wernfried Domscheit

60.4k10 gold badges93 silver badges132 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

glinda93 Over a year ago

Good job! You can try the second query in this link: mongoplayground.net/p/BlCF0jN6vuV

glinda93 Over a year ago

If you don't mind, can you post a map-reduce version of this answer?

Wernfried Domscheit Over a year ago

@bravemaster actually I never used map-reduce yet - so it would be a challenge for me.

Collectives™ on Stack Overflow

how to select all values of particular key from an array of objects

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related