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  1. Core Server
  2. SERVER-11400

Need a type conversion mechanism to convert between strings and numbers

    • Query
    • Query 12 (04/04/16), Query 13 (04/22/16), Query 15 (06/03/16), Query 17 (07/15/16)


      {$toInt: <arbitrary expression>}
      {$toLong: <arbitrary expression>}
      {$toDouble: <arbitrary expression>}
      {$toDecimal: <arbitrary expression>}
      {$toString: <arbitrary expression>}


      > db.coll.insert([
        {_id: 0, x: "3.4"},
        {_id: 1, x: 0.99}
      > db.coll.aggregate([{
        $project: {
          intField: {$toInt: "$x"}
      {_id: 0, intField: 3}
      {_id: 1, intField: 0}
      // Example 2
      > db.coll.insert([
        {_id: 0, x: {a: "b"}},
        {_id: 1, x: 1.22},
        {_id: 2, x: "abc"}
      > db.coll.aggregate([{
        $project: {
          stringField: {$toString: "$x"}
      {_id: 0, stringField: "{a: 'b'}"}
      {_id: 1, stringField: "1.22"}
      {_id: 2, stringField: "abc"}


      • Each numeric conversion can convert from any numeric type or from a string (truncating if necessary).
      • Calling $toInt on an int is a no-op, similarly for other conversions.


      • If the input is of a type or value that cannot be converted:
        $toInt, $toLong, $toDouble, $toDecimal accept only int, long, double, decimal, and strings that can be interpreted as the above. $toString accepts anything that can be turned into output that is parseable by the mongo shell.

      Old Description
      There are situations where I want to use a number as (part of) a string but $concat will only take strings and not numbers. And there are other times where I have a string of a number "2012" and I want to use it as a number and there is no operator to do this.

      Seems painful to fall back to map/reduce solely because someone saves a number or date as a string

            backlog-server-query Backlog - Query Team (Inactive)
            asya.kamsky@mongodb.com Asya Kamsky
            15 Vote for this issue
            29 Start watching this issue