How to inject service to validator constraint interface in nestjs using class-validator?

Question

I'm trying to inject my users service into my validator constraint interface but it doesn't seem to work:

import { ValidatorConstraintInterface, ValidatorConstraint, ValidationArguments, registerDecorator, ValidationOptions } from "class-validator";
import { UsersService } from './users.service';

@ValidatorConstraint({ async: true })
export class IsEmailAlreadyInUseConstraint implements ValidatorConstraintInterface {
    constructor(private usersService: UsersService) {
        console.log(this.usersService);
    }
    validate(email: any, args: ValidationArguments) {
        return this.usersService.findUserByEmail(email).then(user => {
             if (user) return false;
             return true;
        });
        return false;
    }

}

But, as usersService is logged null, I can't access its methods.

Any insight on this matter?

Answer 1

For those who might be suffering from this issue:

class-validator requires you to use service containers if you want to inject dependencies into your custom validator constraint classes. From: https://github.com/typestack/class-validator#using-service-container

import {useContainer, Validator} from "class-validator";

// do this somewhere in the global application level:
useContainer(Container);

So that we need to add the user container function into the global application level.

1. Add the following code to your main.ts bootstrap function after app declaration:

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  useContainer(app.select(AppModule), { fallbackOnErrors: true });
...}

The {fallbackOnErrors: true} is required, because Nest throw Exception when DI doesn't have required class.

2. Add Injectable() to your constraint:

import {ValidatorConstraint, ValidatorConstraintInterface} from 'class-validator';
import {UsersService} from './user.service';
import {Injectable} from '@nestjs/common';

@ValidatorConstraint({ name: 'isUserAlreadyExist', async: true })
@Injectable() // this is needed in order to the class be injected into the module
export class IsUserAlreadyExist implements ValidatorConstraintInterface {
    constructor(protected readonly usersService: UsersService) {}

    async validate(text: string) {
        const user = await this.usersService.findOne({
            email: text
        });
        return !user;
    }
}

3. Inject the constraint into your module as a provider and make sure that the service you intend to inject into your constraint are also available to a module level:

import {Module} from '@nestjs/common';
import { UsersController } from './user.controller';
import { UsersService } from './user.service';
import { IsUserAlreadyExist } from './user.validator';

@Module({
    controllers: [UsersController],
    providers: [IsUserAlreadyExist, UsersService],
    imports: [],
    exports: []
})
export class UserModule {
}