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Showing content from https://github.com/19majkel94/class-transformer-validator below:

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

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

npm install class-transformer-validator --save

(or the short way):

npm i -S class-transformer-validator

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

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(err => {
    // here you can handle error on transformation (invalid JSON)
    // or validation error (e.g. invalid email property)
    console.error(err);
  });

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);
    // infered type of userObject is User, you can access all class prototype properties and methods
  } catch (err) {
    // your error handling
    console.error(err);
  }
};

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 (err) {
    // your error handling
  }
};

There is available the transformAndValidate function with three overloads:

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

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

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

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

Or you can just check the type in runtime using Array.isArray method.

If you need sync validation, use transformAndValidateSync function instead (available since v0.4.0). It will synchronously return T or T[], not a Promise.

• 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 TransformValidationOptions {
  validator?: ValidatorOptions;
  transformer?: ClassTransformOptions;
}

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

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

0.9.1

• widen class-transformer peer dependency version range to >=0.2.3
• updated all dev dependencies

0.9.0

• bump class-validator peer dependency to version >=0.12.0
• updated TypeScript dependency to version ^3.9.5
• updated all dev dependencies

0.8.0

• updated class-transformer dependency to version ^0.2.3
• updated class-validator dependency to version ^0.10.1
• updated TypeScript dependency to version ^3.6.3
• built code is now emitted as ES2015 (dropped es5 support)
• updated all dev dependencies

0.7.1

• updated class-transformer dependency to version ^0.2.0

0.6.0

• updated class-validator dependency to version ^0.9.1

0.5.0

• remove deprecated TransformValdiationOptions interface (typo)
• updated class-validator dependency to version ^0.8.1 and class-transformer to ^0.1.9

0.4.1

• fix TransformValdiationOptions interface name typo (deprecate in favour of TransformValidationOptions)

0.4.0

• added transformAndValidateSync function for synchronous validation
• changed return type for JSON's transform and validation to Promise of T or T[]
• updated 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
• updated 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

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