Write Express Controllers like a pro.

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Write express controllers like a pro

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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.

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,
    },
  });
});
Note
Note that the catchAysync in the above function is just to wrap the function in try-catch block due to the use of async-await. And the AppError is just custom designed error to be passed to the global error controller by doing next(error).
// 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.

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 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);
Note
💡 Note that you can design your own error like AppError. or simply pass some message string and throw an error. You can refer to the bellow code if you wanna implement the AppError module that makes passing errors to the express global error controller easy by just passing the error message and status code as a parameter i.e. next(new AppError(”my error message”, 404)).
// 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;

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