Express + Mongoose Middleware: Standard Controller + Router

app.js

const express = require("express")

const mw = require("./middleware")

const app = express()

app
  .use(express.json())
  .use(express.urlencoded({ extended: true }))
  .use(mw.Book.router)

app.listen(process.env.PORT || 8080)

controller.js

/* middleware/controller.js */

const router = require("express").Router()

/* Require or set up your mongoose models here */
const models = require("./models")

module.exports = class {

  constructor(modelName) {

    if (!models[modelName])
      throw new Error(`Model "${modelName}" not found.`)

    this.Model = models[modelName]
    this.modelName = this.Model.modelName.toLowerCase()
    
    this.routes = {
      base: `/api/${this.modelName}`,
      id: `/api/${this.modelName}/:id`,
      query: `/api/${this.modelName}/query`
    }

  }

  get dbMethods() {

    const getDocs = () => {
      return this.Model.find()
    }

    const queryDocs = (body) => {
      return this.Model.find(body)
    }

    const queryUpdateDocs = (filter, update) => {
      this.Model.findOneAndUpdate(filter, update, { new: true }).exec()
    }

    const createDoc = (body) => {
      const doc = new this.Model(body)
      return doc.save()
    }

    const readDoc = (id) => {
      return this.Model.findById(id)
    }

    const updateDoc = (id, body) => {
      return this.Model.findByIdAndUpdate(id, body, { new: true }).exec()
    }

    const appendChildDoc = (id, body) => {
      return this.Model.findByIdAndUpdate(id, { $push: body }, { new: true }).exec()
    }

    const deleteDoc = (id) => {
      return this.Model.findByIdAndDelete(id).exec()
    }

    return {
      getDocs,
      queryDocs,
      queryUpdateDocs,
      createDoc,
      readDoc,
      updateDoc,
      appendChildDoc,
      deleteDoc
    }

  }

  get requestHandlers() {

    let handleSuccess = (res, result) => {
      return res.status(200).json(result)
    }

    let handleError = (res, error) => {
      console.error(error.message)
      return res.status(500).json({ status: status[500] })
    }

    const retrieveDocuments = (req, res) => {
      this.dbMethods.getDocs()
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const queryDocuments = (req, res) => {
      this.dbMethods.queryDocs(req.body)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const queryUpdateDocuments = (req, res) => {
      this.dbMethods.queryUpdateDocs(req.filter, req.body)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const createDocument = (req, res) => {
      this.dbMethods.createDoc(req.body)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const readDocument = (req, res) => {
      this.dbMethods.readDoc(req.params.id)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const updateDocument = (req, res) => {
      this.dbMethods.updateDoc(req.params.id, req.body)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const appendChildDocument = (req, res) => {
      this.dbMethods.appendChildDoc(req.params.id, req.body)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    const deleteDocument = (req, res) => {
      this.dbMethods.deleteDoc(req.params.id)
        .then(result => handleSuccess(res, result))
        .catch(error => handleError(res, error))
    }

    return {
      retrieveDocuments,
      queryDocuments,
      queryUpdateDocuments,
      createDocument,
      readDocument,
      updateDocument,
      appendChildDocument,
      deleteDocument
    }

  }

  get router() {

    const ctrl = this.requestHandlers

    router.route(this.routes.base)
      .get(ctrl.retrieveDocuments)
      .post(ctrl.createDocument)

    router.route(this.routes.id)
      .get(ctrl.readDocument)
      .put(ctrl.updateDocument)
      .patch(ctrl.appendChildDocument)
      .delete(ctrl.deleteDocument)

    router.route(this.routes.query)
      .post(ctrl.queryDocuments)

    return router

  }

}

index.js

/* middleware/index.js */

const StandardController = require("./controller")

module.exports = {
  Book: new StandardController("Book")   
}