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What is PDO in PHP, and what advantages does it provide over older database extensions like mysqli for interacting with a database? What is a prepared statement in PDO, and why is using one considered essential for writing secure database queries? How do you use named placeholders in a PDO prepared statement, and how do they improve readability compared to positional question mark placeholders? How do database transactions work in PDO, and why are they important for ensuring multiple related database operations either all succeed together or all fail together? How does connection pooling and persistent connections work with PDO, and what tradeoffs should be considered before enabling persistent connections? How should an application handle database connection failures gracefully, including implementing retry logic and connection health checks for a reliable production system?
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How do you configure PDO's error handling mode to ensure database errors are properly reported as catchable exceptions rather than silently failing?

Intermediate

Answer

By setting the PDO::ATTR_ERRMODE attribute to PDO::ERRMODE_EXCEPTION, you configure PDO to throw a proper PDOException whenever a database error occurs, such as a malformed query or a constraint violation, allowing you to handle these errors using standard try catch blocks, which is significantly safer and more reliable than PDO's default silent error mode, where a failed query might otherwise go completely unnoticed unless you manually check for an error after every single database call.
$pdo = new PDO($dsn, $username, $password, [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
]);
Real-world example A development team discovers that a critical database write had been silently failing for weeks due to PDO's default error mode not throwing an exception, and immediately configures ERRMODE_EXCEPTION across their entire application to ensure this kind of silent failure can never happen again.

Common follow-ups: What are the other available PDO error handling modes besides exceptions?;Why is silent error mode considered dangerous for a production application?

Error & Exception Handling;Security
All 7 PDO & Databases questions