Yeah I know these are not express controllers they are Nintendo’s 😅. But If you are bored writing the express controllers the boring way I will share with you a better solution today.

The old way

Let's suppose you have some endpoints related /cars, /bike, etc. And for each of their controller, you wanna define some middleware's related GET, UPDATE, PATCH, and DELETE requests. Let's say you are defining the update middleware first like bellow

exports.updateBike = catchAsync(async (req, res, next) => {
  const bike = await Bike.findByIdAndUpdate(req.params.id, req.body, {
    new: true,
    runValidators: true
  });

  if (!bike) {
    return next(new AppError('No bike found with that ID', 404));
  }

  res.status(200).json({
    status: 'success',
    data: {
      bike
    }
  });
});

// catchAysnc Module

/**
 * making you async function to catch errors
 * without using try-catch explicitly in every function  
*/
**module.exports = fn => {
  return (req, res, next) => {
    fn(req, res, next).catch(next);
  };
};**

And for the /cars endpoint you are repeating the same code.

exports.updateCar = catchAsync(async (req, res, next) => {
  const car = await Car.findByIdAndUpdate(req.params.id, req.body, {
    new: true,
    runValidators: true
  });

  if (!car) {
    return next(new AppError('No car found with that ID', 404));
  }

  res.status(200).json({
    status: 'success',
    data: {
      car
    }
  });
});

So when your app will be growing large it becomes difficult to write the same middleware code for the GET, UPDATE, PATCH, and DELETE functionality, for all the endpoints. There is a better way for defining your code.

Handler Factory.js

You just need to define a controller module once and it will save you from rewriting your code. You can simply change the above two blocks of code to bellow

exports.updateCar = factory.updateOne(Car);

Do the same with bikeController module

exports.updateBike = factory.updateOne(Bike);

You can do the same with all the other CRUD operations as shown.

exports.getAllCars = factory.getAll(Car);
exports.getCar = factory.getOne(Car);
exports.createCar = factory.createOne(Car);
exports.updateCar = factory.updateOne(Car);
exports.deleteCar = factory.deleteOne(Car);

See by just using the factory object we save our time and solve the boilerplate. You just need to implement this hadlerFactory.js module.

Implementing Handler Factory

Implementing this module is similar like implementing the basic controller. You just have to define the controller as a general controller that can be used with your other controllers.

exports.createOne = Model =>
  catchAsync(async (req, res, next) => {
    const doc = await Model.create(req.body);

    res.status(201).json({
      status: 'success',
      data: {
        data: doc
      }
    });
  });

You just have to pass the mongoose Model to the method and it will create a new object in the DB using that model. Similarly, you can write your whole handler.

const catchAsync = require('./../utils/catchAsync');
const AppError = require('./../utils/appError');

exports.deleteOne = Model =>
  catchAsync(async (req, res, next) => {
    const doc = await Model.findByIdAndDelete(req.params.id);

    if (!doc) {
      return next(new AppError('No document found with that ID', 404));
    }

    res.status(204).json({
      status: 'success',
      data: null
    });
  });

exports.updateOne = Model =>
  catchAsync(async (req, res, next) => {
    const doc = await Model.findByIdAndUpdate(req.params.id, req.body, {
      new: true,
      runValidators: true
    });

    if (!doc) {
      return next(new AppError('No document found with that ID', 404));
    }

    res.status(200).json({
      status: 'success',
      data: {
        data: doc
      }
    });
  });

exports.createOne = Model =>
  catchAsync(async (req, res, next) => {
    const doc = await Model.create(req.body);

    res.status(201).json({
      status: 'success',
      data: {
        data: doc
      }
    });
  });

exports.getOne = (Model, popOptions) =>
  catchAsync(async (req, res, next) => {
    let query = Model.findById(req.params.id);
    if (popOptions) query = query.populate(popOptions);
    const doc = await query;

    if (!doc) {
      return next(new AppError('No document found with that ID', 404));
    }

    res.status(200).json({
      status: 'success',
      data: {
        data: doc
      }
    });
  });

So now you can use this factory module while building your other controller.

exports.getAllBikes = factory.getAll(Bike);
exports.getBike = factory.getOne(Bike);
exports.createBike = factory.createOne(Bike);
exports.updateBike = factory.updateOne(Bike);
exports.deleteBike = factory.deleteOne(Bike);

// simply pass err-msg & status code as param to gen an err
class AppError extends Error {
  constructor(message, statusCode) {
    super(message);

    this.statusCode = statusCode;
    this.status = `${statusCode}`.startsWith('4') ? 'fail' : 'error';
    this.isOperational = true;

    Error.captureStackTrace(this, this.constructor);
  }
}

module.exports = AppError;

Acknowledgement

This node.js course helped me implement the above code node.js bootcamp

Originally published at theundersurfers.netlify.app

Imran Zaheer