In this section, we're going to go through the fundamental concepts of working with the database. We will continue with the step-by-step build-up from our previous todo project. You will have noticed that our last project, we were storing our information in computer memory, and that it disappears immediately once our server returns. In real-life, you will want to store this data persistently for later access.

So, what is Knex.js? It is a SQL query-builder for relational databases like PostgreSQL, Microsoft SQL Server, MySQL, MariaDB, SQLite3, and Oracle. Basically, with something like Knex, you can write one code that will easily work with any of the mentioned databases, with no extra effort, just switching the configurations.

Let's walk through the exercise as we explain the concepts.