Mongoose. Get max id when id is a string

Question

I have a table in database (MongoDB) that stores one id field as a string but it is a integer number (for example, original 12 -> in table '12'). Now I need to get a maximum value on this field but maximum at the context that this number is integer. Please, give me solution how to do it? (I can't change type of field in table)

Possible duplicate of [how to convert string to numerical values in mongodb](https://stackoverflow.com/questions/29487351/how-to-convert-string-to-numerical-values-in-mongodb) — dnickless, Oct 04 '18 at 21:05

score 0 · Answer 1 · answered Oct 04 '18 at 16:31

0

One possible way to do this is with aggregation:

db.collectionName.aggregate([{
    $convert: {
        input: "$intButStringKey",
        to: "int"
    }
}, {
    maxValue: {
        $max: "$intButStringKey"
    }
}])

answered Oct 04 '18 at 16:31

Atish

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Akrion · Accepted Answer · 2018-10-04T16:45:38.993

If you are on MongoDb 4.0 and up you can simply use $toInt in something like this:

db.collection.aggregate([
  {
    $group: {
      "_id": "MYFIELD",
      "Max": {
        "$max": {
          "$toInt": "$MYFIELD"
        }
      }
    }
  }
])

OR you can also use $convert:

db.collection.aggregate([
  {
    $group: {
      "_id": "MYFIELD",
      "Max": {
        "$max": {
          "$convert": { "input": "$MYFIELD", "to": "int" }
        }
      }
    }
  }
])

You could also use $addFields to add that int field early in your aggregation:

db.collection.aggregate([
  {
    $addFields: {
      intField: {
        $toInt: "$MYFIELD"
      }
    }
  },
  {
    $group: {
      _id: "$max",
      max: {
        $max: "$intField"
      }
    }
  },
  {
    $project: {
      _id: 0
    }
  }
])

Mongoose. Get max id when id is a string

2 Answers2