class-transformer-validator

A simple plugin for class-transformer and class-validator which combines them in a nice and programmer-friendly API.

Installation

Module installation

npm install class-transformer-validator --save

(or the short way):

npm i -S class-transformer-validator

Peer dependencies

This package is only a simple plugin/wrapper, so you have to install the required modules too because it can't work without them. See detailed installation instruction for the modules installation:

• class-transformer
• class-validator

Usage

The usage of this module is very simple.

import { IsEmail } from 'class-validator';
import { transformAndValidate } from "class-transformer-validator";

// declare the class using class-validator decorators
class User {
    @IsEmail()
    public email: string;

    public hello(): string {
        return "World!";
    }
}

// then load the JSON string from any part of your app
 const userJson: string = loadJsonFromSomething();

// transform the JSON to class instance and validate it correctness
transformAndValidate(User, userJson)
    .then((userObject: User) => {
        // now you can access all your class prototype method
        console.log(`Hello ${userObject.hello()}`); // prints "Hello World!" on console
    })
    .catch(error => {
        // here you can handle error on transformation (invalid JSON)
        // or validation error (e.g. invalid email property)
        console.err(error);
    });

You can also transform and validate plain JS object (e.g. from express req.body). Using ES7 async/await syntax:

async (req, res) => {
    try {
        // transform and validate request body
        const userObject = await transformAndValidate(User, req.body);
        // intered type of userObject is User, you can access all class prototype properties and methods
    } catch (error) {
        // your error handling
        console.err(error);
    }
}

And since release 0.3.0 you can also pass array of objects - all of them will be validated using given class validation constraints:

async (req, res) => {
    try {
        // transform and validate request body - array of User objects
        const userObjects = await transformAndValidate(User, req.body);
        userObjects.forEach(user => console.log(`Hello ${user.hello()}`));
    } catch (error) {
        // your error handling
    }
}

API reference

Function signatures

There is available the transformAndValidate function with three overloads:

function transformAndValidate<T extends object>(classType: ClassType<T>, jsonString: string, options?: TransformValdiationOptions): Promise<T|T[]>;

function transformAndValidate<T extends object>(classType: ClassType<T>, object: object, options?: TransformValdiationOptions): Promise<T>;

function transformAndValidate<T extends object>(classType: ClassType<T>, array: object[], options?: TransformValdiationOptions): Promise<T[]>;

If you need sync validation, use transformAndValidateSync function instead (since v0.4.0).

Be aware that if you validate json string, the return type is a Promise of T or T[] so you need to assert the returned type if you know the shape of json:

const users = transformAndValidate(User, JSON.stringify([{ email: "test@test.test" }])) as User[];

Or you can just check in runtime using Array.isArray(obj) method.

Parameters and types

• classType - an class symbol, a constructor function which can be called with new

type ClassType<T> = { 
    new (...args: any[]): T;
}

• jsonString - a normal string containing JSON

• object - plain JS object of type object (introduced in TypeScript 2.2), you will have compile-time error while trying to pass number, boolean, null or undefined but unfortunately run-time error when passing a function

• array - array of plain JS objects like described above

• options - optional options object, it has two optional properties

interface TransformValdiationOptions {
    validator?: ValidatorOptions;
    transformer?: ClassTransformOptions;
}

You can use it to pass options for class-validator (more info) and for class-transformer (more info).

More info

The class-transformer and class-validator are more powerfull than it was showed in the simple usage sample, so go to their github page and check out they capabilities!

Release notes

0.4.0

• added transformAndValidateSync function for synchronous validation
• changed return type for transform and validation JSON to Promise of T or T[]
• bumped class-validator dependency to version ^0.7.2 and class-transformer to ^0.1.7

0.3.0

• added support for transform and validate array of objects given class
• bumped class-validator dependency to version ^0.7.1

0.2.0

• changed object parameter type declaration to object (introduced in TS 2.2)
• throwing error when passed array, undefined or null

0.1.1

• changed throwing error (rejecting promise) from string to Error with message

0.1.0

• initial version with transformAndValidate function