Change type of a field in a nested array

Working with Data
#1

Hi,

Each document of my collection “histo” has the following schema:

{
    "_id" : ObjectId("5ed61144376edd4a601467cd"),
    "pname" : "actual_speed",
    "values" : [ 
        {
            "timestamp" : 1580120048,
            "val" : 27716
        }, 
        {
            "timestamp" : 1580120113,
            "val" : 27730.5
        }, 
        {
            "timestamp" : 1580120138,
            "val" : 27702
        }, 
       ...
]}

I want to force the type “val” to Double. For the moment, if its value is an integer, as for “27716”, its type is int32.

I tried with:

db.getCollection("histo").find().forEach(function (e) {
  e.values.forEach(function (o) {
      o.val = parseFloat(o.val);
  });
  db.getCollection("histo").save(e);
});

But it does not work.

What is wrong ?

Thanks!

#2

@Helene_ORTIZ

By default, in MongoDB document the type of a number is a double. In the sample document you had posted though the number 27702 is an integer, actually its type is double. This can be verified with the following query:

db.collection.aggregate([ 
  { 
      $addFields: { 
          types: { 
              $map: { input: "$values", in: { type: { $type: "$$this.val" }, val: "$$this.val" } }
          }
      }
  }
]).pretty()
1 Like
#3

Sorrry but in my database the field containing 27702 is an integer in mongoDB.

#4

The following update statement will update all the val field value type to double. Note this update runs in MongoDB version 4.2 or later only.

db.collection.updateMany(
{},
[
  { 
      $set: { 
          values: { 
              $map: { input: "$values", in: { $mergeObjects: [ "$$this", { val: { $toDouble: "$$this.val" } } ] } }
          }
      }
  }
] )

In case your database version is older than 4.2, then use this query:

db.collection.aggregate([ 
  { 
      $addFields: { 
          values: { 
              $map: { input: "$values", in: { $mergeObjects: [ "$$this", { val: { $toDouble: "$$this.val" } } ] } }
          }
      }
  }
] ).forEach( doc => db.collection.updateOne( { _id: doc._id }, { $set: { values: doc.values } } ) )

NOTE: The aggregation operator $toDouble used in the above queries converts a number to a double.

1 Like