updateMany() MongoDB can't Change Field Type

Question

My objective is to change the type of some fields in my documents over my full collection. I want to change some strings to int using $toInt.

I am trying to update the '$helpful' field to be an integer. Here is what my schema looks like in an example document:

  _id: ObjectId("62e32a75a984c054fb986fbf"),
  id: '7',
  product_id: '2',
  body: 'Where is this product made?',
  date_written: '1590428073460',
  asker_name: 'iluvcatz',
  asker_email: 'first.last@gmail.com',
  reported: '0',
  helpful: '0',
  answers: [ ]

When I run this command:

db.question.updateMany({ }, [{ $set: { "helpful": {$toInt: "$helpful"}}}])

I get the following error message:

MongoServerError: Failed to parse number 'helpful' in `$convert` with no onError value: Did not consume whole string.

I have tried modifying my command to change my first parameter of updateMany to filter for things that would include all my helpful field values, like:

{helpful: {$exists: true}}
{helpful: {$type: "string"}}

When I try this as my filter and specify it exactly it works:

{helpful: "0"}

But I have many different string values 0-100 for my helpful field. Any idea why this isn't working?

Answer 1

The error throws because some of the documents have alphabets or special symbols like dot . , You can check the examples when $toInt will throw an error .

There is another operator $convert , I would suggest you use that because it handles error and null values,

• pass default value in onError if it throws an error,
• pass default value in onNull if the value has null value
• both the properties are optional

db.question.updateMany(
  {}, 
  [{ 
    $set: { 
      helpful: {
        $convert: {
          input: "$helpful",
          to: "int",
          onError: null,  // Optional.
          onNull: null    // Optional.
        }
      }
    }
  }]
)

Playground