Chapter 29: Database Migrations in C++

Generate and apply schema changes. In this chapter, you will learn database migrations in depth with C++ code examples, explanations, and best practices.

Overview

This chapter covers database migrations 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 migrations is essential because it is a core part of building web applications. Every real-world app needs to handle generate and apply schema changes. 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++:

let migration = kungfu_orm::generate_migration::<User>();

println!("Migration: {}", migration.name);
for stmt in &migration.up_sql {
    println!("{}", stmt);
    db.execute(stmt, &[]).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 migrations 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 30, we will cover Relationships and JOINs: Connect tables with INNER and LEFT JOIN.