Validation Messages¶

You can specify validation messages in the decorator options and that message will be returned in the ValidationError returned by the validate method (in the case that validation for this field fails).

Basic Usage¶

import { MinLength, MaxLength } from 'class-validator';

export class Post {
    @MinLength(10, {
        message: 'Title is too short',
    })
    @MaxLength(50, {
        message: 'Title is too long',
    })
    title: string;
}

Message Variables¶

There are few special tokens you can use in your messages:

$value - the value that is being validated
$property - name of the object's property being validated
$target - name of the object's class being validated
$constraint1, $constraint2, ... $constraintN - constraints defined by specific validation type

Example:

import { MinLength, MaxLength } from 'class-validator';

export class Post {
    @MinLength(10, {
        message: 'Title is too short. Minimal length is $constraint1 characters, but actual is $value',
    })
    @MaxLength(50, {
        message: 'Title is too long. Maximal length is $constraint1 characters, but actual is $value',
    })
    title: string;
}

Dynamic Messages¶

You can also provide a function that returns a message. This allows you to create more granular messages:

import { MinLength, ValidationArguments } from 'class-validator';

export class Post {
    @MinLength(10, {
        message: (args: ValidationArguments) => {
            if (args.value.length === 1) {
                return 'Too short, minimum length is 1 character';
            } else {
                return 'Too short, minimum length is ' + args.constraints[0] + ' characters';
            }
        },
    })
    title: string;
}

The message function accepts ValidationArguments which contains:

value - the value that is being validated
constraints - array of constraints defined by specific validation type
targetName - name of the object's class being validated
object - object that is being validated
property - name of the object's property being validated