Chapter 21: Database Connection in C#

Connect to SQLite, PostgreSQL, MySQL, Supabase. In this chapter, you will learn database connection in depth with C# code examples, explanations, and best practices.

Overview

This chapter covers database connection for Kungfu.js developers using C#. We will start with the basics, move through practical examples, and end with advanced techniques and common pitfalls.

Why This Matters

Understanding database connection is essential because it is a core part of building web applications. Every real-world app needs to handle connect to sqlite, postgresql, mysql, supabase. Skipping this chapter would leave a gap in your knowledge that would cause problems later.

Code Example

Here is how to work with databases in C#:

// SQLite (local development)
let db = Db::connect(&DbConfig {
    url: "sqlite::memory:".into(),
    max_connections: 5,
    min_connections: 1,
}).await?;

// PostgreSQL (Supabase, Neon, Railway)
let db = Db::connect(&DbConfig {
    url: "postgres://user:pass@host:5432/db".into(),
    max_connections: 10,
    min_connections: 2,
}).await?;

// MySQL
let db = Db::connect(&DbConfig {
    url: "mysql://user:pass@host:3306/db".into(),
    max_connections: 10,
    min_connections: 2,
}).await?;

How the ORM Works

The Kungfu.js ORM uses parameterized queries. This means user input never gets interpolated into SQL strings. Instead, placeholders like $1, $2 are used, and the actual values are passed separately. This makes SQL injection impossible.

For example, if you search for a user by email, the ORM generates: SELECT * FROM users WHERE email = $1 and passes the email value as a parameter. Even if the email contains SQL code like ' OR 1=1 --, it is treated as a plain string, not as SQL.

Common Mistakes

  • Not reading the documentation: Always check the API reference when something does not work as expected.
  • Skipping security: Never disable the default middleware unless you have a very good reason. Security is not optional.
  • Not testing: Write tests for your handlers. Kungfu.js makes this easy with the built-in test utilities.

Summary

In this chapter, you learned about database connection in C#. You saw code examples, understood how things work under the hood, and learned about common mistakes to avoid.

What is Next?

In chapter 22, we will cover Defining Models: Create database models with attributes.

Previous: Cookies and SessionsNext: Defining Models