PDO Error Handling

PHP Data Objects (PDO) provides a consistent interface for accessing databases in PHP.

This guide covers PDO Error Handling with working code you can adapt for your own projects. We will walk through the setup, show what the code actually does at each step, and flag the spots where things tend to break.

If you have worked with PDO before, skip ahead to the code examples. If this is your first time, read the whole thing - the order matters.

How It Works

// db-connect.php
<?php
try {
    $dsn = 'mysql:host=localhost;dbname=testdb;charset=utf8mb4';
    $pdo = new PDO($dsn, 'root', '', [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    ]);
    echo "Connected successfully.";
} catch (PDOException $e) {
    error_log($e->getMessage());
    echo "Database connection failed.";
}
?>

The key idea here: get something running first, then refine. The code above is intentionally minimal so you can see the structure without noise.

Step-by-Step Walkthrough

1. Set up your environment. Make sure your PHP version matches what the framework or library expects. Run php -v to check.
2. Create the base files. Copy the example above into your project directory. Adjust the connection details or paths to match your local setup.
3. Test immediately. Do not write 200 lines before running the code. Test after every meaningful change. This habit catches typos and config errors before they compound.
4. Read the error messages. PHP error messages are verbose for a reason. The file path and line number in the error output will point you to the problem 90% of the time.
5. Refactor once it works. Move hardcoded values into configuration. Extract repeated logic into functions. But only after the basic version runs.

Working with the Code

There are a few things to keep in mind when adapting this for production:

• Error handling is not optional. The examples here use basic try/catch blocks. In production, log errors and show generic messages to users.
• Input validation goes before everything else. If the data comes from a user, treat it as hostile until proven otherwise.
• File paths differ between OS environments. Use the appropriate directory separator or PHP constants like DIRECTORY_SEPARATOR when building paths.

Common Mistakes

• Not checking return values. Functions that fail silently are the hardest bugs to track. Always check what comes back.
• Skipping error reporting during development. Set error_reporting(E_ALL) and display_errors = On locally. Turn display off in production but keep logging on.
• Hardcoding credentials. Even in tutorials, get in the habit of using environment variables or a config file outside the web root.
• Ignoring character encoding. Use UTF-8 everywhere: database, connection string, HTML meta tag. Mismatched encodings cause garbled text that is painful to debug later.
• Copy-pasting without reading. Seriously - read the code before you run it. One wrong table name or missing semicolon will cost you thirty minutes of confusion.

Frequently Asked Questions

Do I need to close a PDO connection manually?

No. PHP closes the connection when the script ends. Setting the PDO variable to null closes it earlier, which matters in long-running scripts.

Can I use PDO with SQLite?

Yes. Change the DSN to "sqlite:/path/to/database.db". The query syntax is standard SQL with minor SQLite-specific differences.

Why does my query return an empty array?

Check that the table and column names match exactly, including case. Also verify the WHERE clause conditions. Run the raw SQL in phpMyAdmin or the CLI first.