I have a collection like this one:

{
"citizen":[
  {
    "country":"ITA",
    "language":"Italian"
  },
  {
    "country":"UK",
    "language":"English"
  },
  {
    "country":"CANADA",
    "language":"French"
  }]
}

I'm trying to update the collection but with a certain condition. I need to update remove an element of the array citizen if the value in the field country is longer than 3 characters.

I got that to remove an element i have to use $pull, to check the size of a string I have to use $strLenCP and $gt is greater than, but I'm struggling to put them together.

The result of the update should be:

{
"citizen":[
  {
    "country":"ITA",
    "language":"Italian"
  },
  {
    "country":"UK",
    "language":"English"
  }]
}

Any suggestions?

EDIT: with the collection, as it is, the command:

db.getCollection('COLLECTION').update(  { }, {  $pull:  {"citizen": {"country": /^[\s\S]{4,}$/}}}, { multi: true })

works perfectly. I tried it on another collection as this one:

{
"cittadino":{
  "citizen":[
    {
      "country":"ITA",
      "language":"Italian"
    },
    {
      "country":"UK",
      "language":"English"
    },
    {
      "country":"CANADA",
      "language":"French"
    }]
  }
}

and it doesn't update anymore. What should i do?