Chapter 28: Database Transactions in C++

BEGIN, COMMIT, ROLLBACK for data integrity. In this chapter, you will learn database transactions in depth with C++ code examples, explanations, and best practices.

Overview

This chapter covers database transactions 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 transactions is essential because it is a core part of building web applications. Every real-world app needs to handle begin, commit, rollback for data integrity. 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++:

db.transaction(|tx| async move {
    tx.execute(
        "INSERT INTO users (email) VALUES ($1)",
        &[json!("alice@example.com")]
    ).await?;
    
    tx.execute(
        "INSERT INTO logs (msg) VALUES ($1)",
        &[json!("user created")]
    ).await?;
    
    Ok(())  // commits
}).await?;  // if this returns Err, ROLLBACK is automatic

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 transactions 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 29, we will cover Database Migrations: Generate and apply schema changes.