question: support for validating property as string or string[]

Hi, how could I validate a string or array of strings?

I have in my class:

@IsString()
public parameter: string | string[];

Is there a way to tell to class-validator that the parameter could be string or array?

[UrielCh]

No Answer for a whole year…

Proper fix

The proper way would be to change interface ValidationOptions, replacing each?: boolean; by each?: boolean | "optional"; then add some changes in customValidations and change in ‘ValidationExecutor’ and update the error message generation logic.

Please let me know if you think I should try a PR.

Quick fix

For now, the easiest way is to write your validator:

File: IsStringOrStrings.ts

import { buildMessage, ValidateBy, ValidationOptions } from 'class-validator';

export const IS_STRING_OR_STRINGS = 'isStringOrStrings';

/**
 * Checks if value is an integer.
 */
export function isStringOrStrings(val: unknown): boolean {
  if (typeof val === 'string') return true;
  if (!Array.isArray(val)) return false;
  for (const v of val) {
    if (typeof v !== 'string') return false;
  }
  return true;
}

/**
 * Checks if value is an String or a Strings.
 * Do not set each: true, or except if your looking for a string[] or string[][]
 */
export function IsStringOrStrings(validationOptions?: ValidationOptions): PropertyDecorator {
  return ValidateBy(
    {
      name: IS_STRING_OR_STRINGS,
      validator: {
        validate: (value: unknown /*, args*/): boolean => isStringOrStrings(value),
        defaultMessage: buildMessage((eachPrefix) => eachPrefix + '$property must be a string of string array', validationOptions),
      },
    },
    validationOptions,
  );
}

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