How do I capitalize the first letter of a string in mongoDB?

Question

I have the following document in my MongoDB:

{
    name: "BRIAN"
}

I'm trying to change it to this format:

{
    name: "Brian"
}

I've tried the following:

{
    $project: {
       name: { $concat: [ { $toLower: '$name' } ]}
    }
}

So this makes the string lowercase, then I just need to make the first letter uppercase. Is it possible to do that within the same project aggregation?

Answer 1

As @Wernfried Domscheit suggested, you can use $substrCP to segment name and perform $toLower separately for the "tail" and keep the first character upper case. Use $concat to put back the 2 results together.

db.collection.update({},
[
  {
    "$addFields": {
      "name": {
        "$concat": [
          {
            "$substrCP": [
              "$name",
              0,
              1
            ]
          },
          {
            "$toLower": {
              "$substrCP": [
                "$name",
                1,
                {
                  "$strLenCP": "$name"
                }
              ]
            }
          }
        ]
      }
    }
  }
],
{
  multi: true
})

Mongo Playground