Is it Possible to Use Sequelize.js with MongoDB?

Introduction

Sequelize is a popular promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication, and more. However, Sequelize was designed to work with relational databases, not NoSQL databases like MongoDB. This article explores the feasibility of using Sequelize.js with MongoDB and provides alternative solutions for those needing to work with this NoSQL database.

Understanding the ORM and ODM Paradigms

Before delving into Sequelize and MongoDB, it’s crucial to understand the difference between an Object-Relational Mapper (ORM) like Sequelize and an Object Document Mapper (ODM). ORMs are designed to work with relational databases and map table rows to objects in the code. In contrast, ODMs are tailored for NoSQL databases, which store data in a non-tabular format, and map document data to objects in the application. MongoDB, as a NoSQL database, is best managed through an ODM, with Mongoose being the most popular one for MongoDB and Node.js.

Why Sequelize Isn’t Ideal for MongoDB

Using Sequelize for MongoDB would be trying to fit a square peg into a round hole. Sequelize’s API and features are geared towards the structured world of SQL. MongoDB stores data in flexible, schema-less documents which makes it fundamentally different from the relational paradigm and thus, incompatible with Sequelize’s core design.

Alternative Solutions

For those working with MongoDB, Mongoose is highly recommended. Here’s a basic usage example of setting up Mongoose with MongoDB, instead of using Sequelize:

const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/myapp', {useNewUrlParser: true, useUnifiedTopology: true});
const Schema = mongoose.Schema;
const BlogPost = new Schema({
  title: String,
  body: String,
  date: Date
});
const Blog = mongoose.model('Blog', BlogPost);

Now, for comparison, here’s an equivalent Sequelize setup for a SQL database:

const Sequelize = require('sequelize');
const sequelize = new Sequelize('database', 'username', 'password', {
  dialect: 'mysql',
  host: 'localhost'
});
const BlogPost = sequelize.define('Blog', {
  title: Sequelize.STRING,
  body: Sequelize.TEXT,
  date: Sequelize.DATE
});

Advanced Usage with Mongoose

While naughtily not using Sequelize with MongoDB, Mongoose provides advanced features that are similar to Sequelize’s offerings. For instance, we can create complex validation, set defaults, and write custom model instance methods:

const BlogPost = new Schema({
  title: { type: String, required: true },
  body: { type: String, required: true },
  date: { type: Date, default: Date.now },
  tags: [{ type: String }]
});

BlogPost.methods.summary = function () {
  return `${this.title} - ${this.date.toLocaleDateString()}`;
};

const Blog = mongoose.model('Blog', BlogPost);
let post = new Blog({
  title: 'My first blog post',
  body: 'Content of the first post.',
  tags: ['new', 'featured']
});
console.log(post.summary());

Advanced features such as relationships (akin to Sequelize’s associations) can also be implemented in Mongoose with the use of references and population. Here’s an example establishing a one-to-many relationship between blog posts and comments:

const CommentSchema = new Schema({
  text: { type: String, required: true },
  author: { type: String, required: true }
});
const Comment = mongoose.model('Comment', CommentSchema);
BlogPost.add({ comments: [{ type: Schema.Types.ObjectId, ref: 'Comment' }] });

Conclusion

In conclusion, Sequelize is not designed to work with MongoDB, and the attempt to do so would go against the grain of both the library’s purpose and the database’s design. Instead, using Mongoose as an ODM is the appropriate approach when working with MongoDB in a Node.js environment. By leveraging the right tools as they were intended, developers can create efficient, scalable, and maintainable applications aligned with the nuances of their chosen database system.