Dependecy Injection using Class into Express

Question

I'm using Express into a TypeScript project and I have the following situation

This is my route file

...
import findAllUsersFactory from "src/factory/FindAllUsers";

routes.get("/users", findAllUsersFactory().handle);
...

This is the factory where I do a sequence of injections

const findAllUsersFactory = () => {
  const findAllUserRepository = new PrismaUsersRepository();
  const findAllUsersBusiness = new FindAllUsersBusiness(findAllUserRepository);
  const findAllUsersController = new FindAllUsersController(findAllUsersBusiness);

  return findAllUsersController;
};

This is my Controller

class FindAllUsersController {
  constructor(private findUserBusiness: FindAllUsersBusiness) { }
  async handle(request: Request, response: Response) {
    const allUsers = await this.findUserBusiness.execute();

    return response.status(200).send({ allUsers });
  }
}

And finally my Business

class FindAllUsersBusiness {
  constructor(private usersRepository: IUsersRepository) {}

  async execute() {
    return this.usersRepository.findAll();
  }
}

The problem is that I'm getting an error "Cannot read property 'execute' of undefined" because the findUserBusiness into handle function is undefined. And what I can't understand is that if I change my route to

routes.get("/users", (request, response) => {
  findAllUsersFactory().handle(request, response);
});

it works

I've tried to log the functions, but I can say why findUserBusiness is undefined since it came from the constructor, and since the handle functions came from an instance of FindAllUsersController it should have it "defined"

Answer 1

You need to make some adjustments in order to adapt your factory to the way router.get expects its parameters.

const findAllUsersFactory = (req, res) => {
  const findAllUserRepository = new PrismaUsersRepository();
  const findAllUsersBusiness = new FindAllUsersBusiness(findAllUserRepository);
  const findAllUsersController = new FindAllUsersController(findAllUsersBusiness);

  return findAllUsersController.handle(req, res)
};

Then in your router you need to do the following:

routes.get("/users", findAllUsersFactory);