What is the best way to implement a decorator for a class method variable within a NestJS framework?

Question

What is the best way to implement a decorator for a class method variable within a NestJS framework?

import {isNotEmpty} from "class-validator";

export Service   {

create(createdto)
{
const {name,age} = createdto;

@isNotEmpty()
name          //applying a decorator to ensure name is not null or undefined
} 
}

As the decorator is designed for class methods, it cannot be applied to method variables directly. Is there a way to validate these variables?

javascript typescript nestjs decorator

Answer 1

Answer №1

Due to the lack of support for decorators on local variables in ECMAScript2016/Typescript, it is not possible to use decorators in the service as described in the question.

However, class-validator offers a non-decorator implementation for its validation functions.

The class-validator Github page states: https://github.com/typestack/class-validator#manual-validation

The Validator has various methods that allow non-decorator based validation:

import { isEmpty, isBoolean } from 'class-validator';

isEmpty(value); isBoolean(value);

Therefore, the same goal can be achieved with code similar to this:

import { Injectable } from "@nestjs/common";
import { CreateDto } from "./dto/create.dto";
import { isEmpty, isInt } from "class-validator";

@Injectable()
export class TestValidationService {
  test(createDto: CreateDto) {
    const {name, age} = createDto;
    
    if (isEmpty(name)) {
      throw "There is no name.";
    }
    
    if (!isInt(age)) {
      throw "Age is not int."
    }
    
    return createDto;
  }
}

If you prefer not to use individual methods within the service, you can still decorate your DTO and use the validate method from class-validator.

For example:

import { IsInt, IsNotEmpty } from "class-validator";

export class CreateDto {
  @IsNotEmpty()
  name: string;
  
  @IsInt()
  age: number
}

And in your service:

async testWithValidate(createDto: CreateDto) {
    const validationResult = await validate(createDto);
}

Answer 2

Due to the lack of support for decorators on local variables in ECMAScript2016/Typescript, it is not possible to use decorators in the service as described in the question.

However, class-validator offers a non-decorator implementation for its validation functions.

The class-validator Github page states: https://github.com/typestack/class-validator#manual-validation

The Validator has various methods that allow non-decorator based validation:

import { isEmpty, isBoolean } from 'class-validator';

isEmpty(value); isBoolean(value);

Therefore, the same goal can be achieved with code similar to this:

import { Injectable } from "@nestjs/common";
import { CreateDto } from "./dto/create.dto";
import { isEmpty, isInt } from "class-validator";

@Injectable()
export class TestValidationService {
  test(createDto: CreateDto) {
    const {name, age} = createDto;
    
    if (isEmpty(name)) {
      throw "There is no name.";
    }
    
    if (!isInt(age)) {
      throw "Age is not int."
    }
    
    return createDto;
  }
}

If you prefer not to use individual methods within the service, you can still decorate your DTO and use the validate method from class-validator.

For example:

import { IsInt, IsNotEmpty } from "class-validator";

export class CreateDto {
  @IsNotEmpty()
  name: string;
  
  @IsInt()
  age: number
}

And in your service:

async testWithValidate(createDto: CreateDto) {
    const validationResult = await validate(createDto);
}

What is the best way to implement a decorator for a class method variable within a NestJS framework?

Answer №1

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