What is the method to restrict the length of a string in Firebase?

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There is no direct method to restrict the length of a string in Firebase. However, you can use the Firebase security rules to validate the length of the string before it is saved to the database.

Here is an example of a security rule that restricts the length of a string to be between 1 and 100 characters:

{
  "rules": {
    "myData": {
      "$stringField": {
        ".validate": "newData.isString() && newData.val().length >= 1 && newData.val().length <= 100"
      }
    }
  }
}

In this rule, myData is the path to the data you want to restrict, and $stringField is a wildcard for the key of the string field. The .validate rule checks that the new data is a string and its length is between 1 and 100 characters. If the validation fails, the write operation will be rejected.