Error handling with PDO exceptions in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch PDO exceptions.

PHP

<?php
try {
    $pdo = new PDO($dsn, $user, $pass);
} catch ([1] $e) {
    echo 'Connection failed: ' . $e->getMessage();
}
?>

Drag options to blanks, or click blank then click option'

AException

BPDOException

CErrorException

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic Exception instead of PDOException.

Misspelling the exception class name.

The PDOException class is used to catch errors related to PDO database operations.

2fill in blank

medium

Complete the code to set PDO to throw exceptions on error.

PHP

<?php
$pdo = new PDO($dsn, $user, $pass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, [1]);
?>

Drag options to blanks, or click blank then click option'

APDO::ERRMODE_EXCEPTION

BPDO::ERRMODE_WARNING

CPDO::ERRMODE_FATAL

DPDO::ERRMODE_SILENT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ERRMODE_SILENT which does not throw exceptions.

Using an invalid constant.

Setting PDO::ATTR_ERRMODE to PDO::ERRMODE_EXCEPTION makes PDO throw exceptions on errors.

3fill in blank

hard

Fix the error in the catch block to correctly get the error message.

PHP

<?php
try {
    $pdo = new PDO($dsn, $user, $pass);
} catch (PDOException $e) {
    echo 'Error: ' . $e->[1]();
}
?>

Drag options to blanks, or click blank then click option'

AerrorMessage

Bmessage

CgetError

DgetMessage

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access a property instead of calling a method.

Using a non-existent method name.

The getMessage() method returns the error message from the exception.

4fill in blank

hard

Fill both blanks to create a try-catch block that connects and sets error mode.

PHP

<?php
try {
    $pdo = new PDO([1], $user, $pass);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, [2]);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}
?>

Drag options to blanks, or click blank then click option'

A$dsn

BPDO::ERRMODE_SILENT

CPDO::ERRMODE_EXCEPTION

D$dsnString

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name for DSN.

Setting error mode to silent instead of exception.

The variable $dsn holds the data source name string, and setting error mode to PDO::ERRMODE_EXCEPTION enables exception throwing.

5fill in blank

hard

Fill all three blanks to create a safe PDO connection with error handling.

PHP

<?php
try {
    $pdo = new PDO([1], [2], [3]);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    echo 'Failed: ' . $e->getMessage();
}
?>

Drag options to blanks, or click blank then click option'

A$dsn

B$user

C$pass

D$database

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of parameters.

Using undefined variables.

The PDO constructor requires the DSN string, username, and password in that order.

Practice

1. What is the main purpose of using try and catch blocks when working with PDO exceptions in PHP?

easy

A. To create new database tables

B. To handle database errors without stopping the entire program

C. To automatically fix SQL syntax errors

D. To speed up database queries

Solution

1. Step 1: Understand the role of try-catch

   The try block runs code that might cause an error, and catch handles that error safely.

2. Step 2: Relate to PDO exceptions

   PDO exceptions occur on database errors; using try-catch prevents the program from stopping abruptly.

3. Final Answer:

   To handle database errors without stopping the entire program -> Option B

4. Quick Check:

   try-catch handles errors safely = D [OK]

Hint: Try-catch blocks catch errors to keep programs running [OK]

Common Mistakes:

• Thinking try-catch speeds up queries
• Believing it fixes SQL errors automatically
• Confusing error handling with database creation

2. Which of the following is the correct way to set PDO to throw exceptions on errors?

easy

A. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT);

B. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);

C. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

D. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_IGNORE);

Solution

1. Step 1: Identify PDO error modes

   PDO supports error modes: SILENT, WARNING, EXCEPTION, and IGNORE (not standard).

2. Step 2: Choose the mode that throws exceptions

   PDO::ERRMODE_EXCEPTION makes PDO throw exceptions on errors.

3. Final Answer:

   $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); -> Option C

4. Quick Check:

   Exception mode = PDO::ERRMODE_EXCEPTION = B [OK]

Hint: Use ERRMODE_EXCEPTION to get PDO exceptions [OK]

Common Mistakes:

• Using ERRMODE_SILENT which hides errors
• Confusing ERRMODE_WARNING with exceptions
• Using non-existent ERRMODE_IGNORE

3. What will be the output of this PHP code?

$pdo = new PDO('sqlite::memory:');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
try {
    $pdo->exec('CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)');
    $pdo->exec('INSERT INTO users (id, name) VALUES (1, "Alice")');
    $pdo->exec('INSERT INTO users (id, name) VALUES (1, "Bob")');
    echo "Insert successful";
} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}

medium

A. Insert successful

B. Syntax error in SQL statement

C. No output

D. Error: SQLSTATE[23000]: Integrity constraint violation: UNIQUE constraint failed: users.id

Solution

1. Step 1: Understand the code flow

   The code creates a table with a primary key on 'id' and inserts two rows with the same id=1.

2. Step 2: Identify the error

   Inserting duplicate primary keys causes an integrity constraint violation, triggering a PDOException.

3. Final Answer:

   Error: SQLSTATE[23000]: Integrity constraint violation: UNIQUE constraint failed: users.id -> Option D

4. Quick Check:

   Duplicate primary key causes exception = C [OK]

Hint: Duplicate primary keys cause PDOException errors [OK]

Common Mistakes:

• Expecting 'Insert successful' despite duplicate keys
• Thinking it's a syntax error
• Ignoring exception handling output

4. Identify the error in this PHP code snippet that uses PDO exceptions:

try {
    $pdo = new PDO('mysql:host=localhost;dbname=testdb', 'user', 'pass');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec('INVALID SQL');
} catch (PDOException $e) {
    echo 'Error: ' . $e->getMessage();
}

medium

A. SQL statement is invalid causing exception

B. Error mode is not set to exceptions

C. PDO connection string is incorrect

D. Missing catch block for exceptions

Solution

1. Step 1: Check PDO connection and error mode

   The connection string and error mode setting are correct for throwing exceptions.

2. Step 2: Analyze the SQL statement

   The SQL statement 'INVALID SQL' is not valid SQL, so it triggers a PDOException.

3. Final Answer:

   SQL statement is invalid causing exception -> Option A

4. Quick Check:

   Invalid SQL causes exception = A [OK]

Hint: Invalid SQL triggers PDOException if error mode set [OK]

Common Mistakes:

• Assuming connection string is wrong
• Forgetting error mode is set correctly
• Thinking catch block is missing

5. You want to safely insert user data into a database using PDO and handle errors with exceptions. Which of the following code snippets correctly implements this with prepared statements and exception handling?

hard

A. try {
$pdo = new PDO($dsn, $user, $pass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)');
$stmt->execute([':name' => $name, ':email' => $email]);
echo 'User added';
} catch (PDOException $e) {
echo 'Error: ' . $e->getMessage();
}

B. $pdo = new PDO($dsn, $user, $pass);
$stmt = $pdo->query('INSERT INTO users (name, email) VALUES ($name, $email)');
echo 'User added';

C. try {
$pdo = new PDO($dsn, $user, $pass);
$stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (?, ?)');
$stmt->execute([$name, $email]);
echo 'User added';
} catch (Exception $e) {
echo 'Error';
}

D. try {
$pdo = new PDO($dsn, $user, $pass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
$pdo->exec('INSERT INTO users (name, email) VALUES ("$name", "$email")');
echo 'User added';
} catch (PDOException $e) {
echo 'Error: ' . $e->getMessage();
}

Solution

1. Step 1: Check for proper error mode setting

   try { $pdo = new PDO($dsn, $user, $pass); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)'); $stmt->execute([':name' => $name, ':email' => $email]); echo 'User added'; } catch (PDOException $e) { echo 'Error: ' . $e->getMessage(); } sets PDO::ATTR_ERRMODE to ERRMODE_EXCEPTION, enabling exception handling.

2. Step 2: Verify use of prepared statements and parameter binding

   try { $pdo = new PDO($dsn, $user, $pass); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)'); $stmt->execute([':name' => $name, ':email' => $email]); echo 'User added'; } catch (PDOException $e) { echo 'Error: ' . $e->getMessage(); } uses prepared statements with named parameters and executes safely with user data.

3. Step 3: Confirm exception handling

   try { $pdo = new PDO($dsn, $user, $pass); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)'); $stmt->execute([':name' => $name, ':email' => $email]); echo 'User added'; } catch (PDOException $e) { echo 'Error: ' . $e->getMessage(); } catches PDOException and outputs the error message, providing safe error handling.

4. Final Answer:

   try { $pdo = new PDO($dsn, $user, $pass); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $stmt = $pdo->prepare('INSERT INTO users (name, email) VALUES (:name, :email)'); $stmt->execute([':name' => $name, ':email' => $email]); echo 'User added'; } catch (PDOException $e) { echo 'Error: ' . $e->getMessage(); } -> Option A

5. Quick Check:

   Prepared + ERRMODE_EXCEPTION + try-catch = A [OK]

Hint: Use prepared statements with ERRMODE_EXCEPTION and try-catch [OK]

Common Mistakes:

• Not setting error mode to exceptions
• Using query() with unescaped variables
• Catching generic Exception instead of PDOException
• Using ERRMODE_WARNING which doesn't throw exceptions