PHP Error Handling in DB

Database error handling is about being ready when things go wrong, like having a plan if the school bus breaks down. PHP catches the problem and responds politely instead of crashing.

In this page:

Catching Database Exceptions
Reading Error Codes
Custom Error Loggers
MySQLi Connection Errors
Suppressing Sensitive Details

Syntax

php

try {
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->query("SQL statement");
} catch (PDOException $e) {
    error_log($e->getMessage());   // log details, show a friendly message
}

Catching Database Exceptions

Database operations can fail for many reasons — a lost connection, a constraint violation, a syntax error in a query — and how your code reacts to those failures determines whether a user sees a clear message or a broken page.

Example: Catching Database Exceptions

php

<?php
// Try running this block; jump to `catch` if it throws
try {
    // Create a new `PDO` instance with 'sqlite::memory:', stored in `$pdo`
    $pdo = new PDO('sqlite::memory:');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec("SELECT * FROM missing_table");
// Catch PDOException $e
} catch (PDOException $e) {
    // Print "A clear error was caught instead of a broken page" to the output
    echo "A clear error was caught instead of a broken page";
}
?>

Reading Error Codes

Setting PDO::ATTR_ERRMODE to PDO::ERRMODE_EXCEPTION (or checking mysqli_error() after each mysqli call) ensures database failures surface immediately instead of being silently ignored and causing confusing bugs downstream.

Example: Reading Error Codes

php

<?php
// Create a new `PDO` instance with 'sqlite::memory:', stored in `$pdo`
$pdo = new PDO('sqlite::memory:');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// Print "Errors will now surface immediately as exceptions" to the output
echo "Errors will now surface immediately as exceptions";
?>

Custom Error Loggers

Wrapping database calls in a try/catch block lets you catch a PDOException specifically, log the technical details for developers, and show the end user a friendly, non-technical error message instead.

Example: Custom Error Loggers

php

<?php
// Try running this block; jump to `catch` if it throws
try {
    // Create a new `PDO` instance with 'sqlite::memory:', stored in `$pdo`
    $pdo = new PDO('sqlite::memory:');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec("SELECT * FROM missing_table");
// Catch PDOException $e
} catch (PDOException $e) {
    // Call `error_log($e->getMessage())`
    error_log($e->getMessage());
    // Print "Something went wrong. Please try again." to the output
    echo "Something went wrong. Please try again.";
}
?>

MySQLi Connection Errors

Never display raw database error messages directly to end users — they can leak details about your schema or query structure that an attacker could use, and are generally meaningless to a non-technical visitor anyway.

Example: MySQLi Connection Errors

php

<?php
try {
    $pdo = new PDO('sqlite::memory:');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec("SELECT * FROM missing_table");
} catch (PDOException $e) {
    // Never echo $e->getMessage() directly to the visitor -- it can leak schema details
    echo "An error occurred.";
}
?>

Suppressing Sensitive Details

Logging the full exception (including the query and parameters, but never raw passwords) to a server-side log file gives you the detail you need to debug an issue without exposing anything sensitive to the public.

Example: Suppressing Sensitive Details

php

<?php
// Try running this block; jump to `catch` if it throws
try {
    // Create a new `PDO` instance with 'sqlite::memory:', stored in `$pdo`
    $pdo = new PDO('sqlite::memory:');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec("SELECT * FROM missing_table");
// Catch PDOException $e
} catch (PDOException $e) {
    // Call `error_log("DB error: " . $e->getMessage())`
    error_log("DB error: " . $e->getMessage());
    // Print "Logged for developers, hidden from the visitor." to the output
    echo "Logged for developers, hidden from the visitor.";
}
?>

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