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Multiple database connections in objectionjs and knex

Eduardo P. Rivero
Javascript developer, 900 days duolingo streak
Originally published at blog.eperedo.com ・2 min read

Normally you have one database for your app, but when your app starts to grow it's normal to create more databases to handle more traffic in an efficient way.
So the question is:

Is objectionjs ready for this?

Spoiler Alert: YES.

Let's assume we have 2 databases called: db_one and db_two

and what we want to achieve is to connect one of our objectionjs Models to the database db_one and the other one to the database db_two.

Let's start creating our models.

// models/Product.js
const { Model } = require("objection");

class Product extends Model {
  static get tableName() {
    return "products";
  }
}

module.exports = Product;

// models/Category.js

const { Model } = require("objection");

class Category extends Model {
  static get tableName() {
    return "categories";
  }
}

module.exports = Category;

Nothing new here, but how can we tell objectionjs to give our models a specific database connection?

Introducing bindKnex

Every objectionjs model has this method called bindKnex and it accepts one parameter: a valid knexjs database connection. And it will return the same model, but binded to a knexjs connection.

Let's see the code to have a better understanding of it.

// index.js

const Knex = require("knex");

// connection for our db_one database
const cnDbOne = Knex({
  client: "mysql2",
  connection: {
    database: "localhost",
    user: "root",
    password: "root",
    database: "db_one"
  }
});

// connection for our db_two database
const cnDbTwo = Knex({
  client: "mysql2",
  connection: {
    database: "localhost",
    user: "root",
    password: "root",
    database: "db_two"
  }
});

// require our models

const ProductModel = require("./models/Product.js");

const CategoryModel = require("./models/Category.js");

const Product = ProductModel.bindKnex(cnDbOne);

const Category = CategoryModel.bindKnex(cnDbTwo);

// making queries

// db_one
// select * from products
Product.query().then(console.log);

// db_two
// select * from categories
Category.query().then(console.log);

Now we can execute our application

node index.js

and each model will make a query to a different database.

We can easily check this using the SHOW PROCESSLIST sql query in our mysql terminal.

SHOW PROCESSLIST;

Terminal console showing multiple database connections

and you can see our app has generated two connections for each database.

That's it! 🚀

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