Repository Pattern for node.js using mongoose

Question

I am a newbie to node.js, coming from a .net background. I would like to use some of the design patterns I used with c#.net. I am running into a few complications however, due to the differences in object oriented nature between c# and JavaScript.

In particular, I would like to implement the repository pattern but have not been able to find a lot of examples doing this with node. The way JavaScript and mongoose are set up are making it a little hard to wrap my mind around this one.

I was referred to the following url for an example https://github.com/iainjmitchell/mongorepositiory, I could be wrong, but I do not see where this example allows for you to pass callbacks that would allow your code to handle any errors that may arise after the db call is made as opposed to how it is ordinarily done using mongoose.

Answer 1

I will explain two functionality of CRUD operation i.e. Create and Read and you will have the idea for rest. We will have the following layer:

• controller
• service
• repository

Let first set up our model using mongoose schema. This is inside the test.model.js.

var mongoose = require("mongoose");
var Schema = mongoose.Schema;

var userSchema = new mongoose.Schema({
  username: String,
  password: String, //hash created from password
  created_at: { type: Date, default: Date.now }
});

module.exports = mongoose.model("User", userSchema);

I will not explain how the controller will request a service layer for posting or receiving the data. It is just about calling a method from the service layer. So inside service layer, for sake of example say test.service.js. we will request repository layer like below. Provide the path for the repository and for your model as your folder structure.

const repository = require("../../models/repository");
var mongoose = require("mongoose");
var User = mongoose.model("User");

function createTestData(user1) {
  return new Promise(function(resolve, reject) {
    let user = new User(user1);// user1 is a object to be saved
    repository
      .create(user)
      .then(data => {
        resolve({
          data: data
        });
      })
      .catch(err => {
        reject(err);
      });
  });
}

function listTestData() {
  let params = {
    limit: 10
  };
  return new Promise(function(resolve, reject) {
    repository
      .list(User, params)
      .then(data => resolve(data))
      .catch(err => reject(err));
  });
}

Now we will create a repository so that every other service can call this repository for CRUD functionality. This will help to reduce boilerplate code.

function create(Model) {
  return new Promise((resolve, reject) => {
    Model.save(function(err, user) {
      if (err) {
        reject(err);
      }
      resolve(user);
    });
  });
}

function list(Model, queryParams) {
  return new Promise((resolve, reject) => {
    Model.find({})
      .limit(parseInt(queryParams.limit))
      .exec(function(err, data) {
        if (err) reject(err);
        resolve(data);
      });
  });
}

That's all. I have tried to explain as simple as possible. You may need to configure other settings like to connect to the database. But if you can make this work you can add other functionality to the repository.