Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 211-225.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 211-225.


25 min read

Table of contents

Embark on an exploration of advanced database concepts and PHP development strategies in this comprehensive segment. Delve into the realm of full-text search in MySQL and its implementation.

Understand MySQL procedures and the role of cursors. Navigate MySQL deadlocks and grasp the impact of JOIN order on query execution plans. Learn how to extract product data and prices from online stores using PHP and consider essential considerations. Dive into message queue implementation using MySQL to enhance data processing efficiency.

Tackle real-world challenges, including parsing API data for exchange rates, creating basic routing systems, architecting with abstractions and traits, crafting intricate SQL queries, and building custom Laravel Artisan commands.

Unravel techniques to access private class properties and address null parameter issues in methods. Explore ReactPHP, Swoole, sensitive data storage, display in logs, and PHP features for concealing data in debug messages.

211. What is full-text search in MySQL? How is it implemented?

Formal Explanation: Full-text search in MySQL is a search technique that allows users to search for words or phrases within the content of textual columns, such as VARCHAR or TEXT. It enables more advanced searches than simple keyword matching, allowing for relevance ranking and stemming. Full-text search is implemented using a special type of index called the full-text index.

Simplified Explanation: Full-text search in MySQL helps you find specific words or phrases within text columns, like a more intelligent search. It uses a special type of index to make searching faster.

Detailed Explanation: Full-Text Search Implementation: MySQL's full-text search is implemented using a specialized index structure called the full-text index. This index stores information about the words and their positions in the indexed text columns, allowing for efficient text-based searches.

Example: Consider a "Articles" table with a "content" column containing the text of various articles. To perform a full-text search, follow these steps:

  1. Creating a Full-Text Index: Before you can perform a full-text search, you need to create a full-text index on the column you want to search. For example:

     CREATE FULLTEXT INDEX idx_content ON Articles(content);
  2. Performing a Full-Text Search: Once the full-text index is created, you can use the MATCH and AGAINST keywords to perform full-text searches. For example, to find articles containing the word "technology":

     SELECT * FROM Articles WHERE MATCH(content) AGAINST('technology');

    This query returns all rows where the "content" column contains the word "technology."

  3. Relevance Ranking: Full-text search also supports relevance ranking, which means the results are ranked based on how closely they match the search terms. For example:

     SELECT * FROM Articles WHERE MATCH(content) AGAINST('technology' IN BOOLEAN MODE);

    This query returns rows with the word "technology," and the results are ranked based on relevance.

  4. Boolean Mode: The IN BOOLEAN MODE modifier allows for more advanced full-text search operations. You can use operators like +, -, and * to refine your search.

Benefits of Full-Text Search:

  • Natural Language Queries: Users can perform searches using natural language phrases.

  • Relevance Ranking: Results are ranked by relevance, making it easier to find the most relevant matches.

  • Stemming and Synonyms: Full-text search handles word variations and synonyms.

  • Speed: Full-text indexes significantly improve search performance for large text-based datasets.

Example Scenario: Imagine a news website with an "Articles" section. Users can search for articles related to specific topics. With full-text search, users can enter search queries like "latest technology trends," and the system will retrieve relevant articles based on the content.

In summary, full-text search in MySQL allows for advanced text-based searches by creating a specialized index structure that enhances search efficiency and relevance ranking. It's particularly useful for applications that deal with textual content, such as news websites, blogs, and knowledge bases.

212. What is a cursor in MySQL procedures?

Formal Explanation: A cursor in MySQL procedures is a database object that allows you to retrieve and manipulate rows from a result set, typically generated by a SELECT statement. Cursors are mainly used within stored procedures to iterate through the rows of a query result and perform operations on each row individually.

Simplified Explanation: A cursor in MySQL procedures is like a pointer that helps you go through rows one by one from the result of a query inside a stored procedure.

Detailed Explanation: In more detail, here's how a cursor works within a MySQL procedure:

1. Declaration and Opening: First, you declare a cursor and associate it with a specific query's result set. Then, you open the cursor to start fetching rows.

DECLARE cursor_name CURSOR FOR SELECT column1, column2 FROM table_name;
OPEN cursor_name;

2. Fetching and Processing: You fetch rows from the result set using the FETCH statement and process each row.

DECLARE variable1 datatype;
DECLARE variable2 datatype;

FETCH cursor_name INTO variable1, variable2;
-- Process the fetched row

3. Looping: You usually loop through the result set using a loop construct.

WHILE condition DO
    -- Fetch and process rows

4. Closing: After processing all rows, you close the cursor.

CLOSE cursor_name;

Example Scenario: Let's say you have an "Orders" table, and you want to calculate the total amount of all orders for each customer using a stored procedure. You would use a cursor to iterate through the rows of the query result for each customer, calculate the total, and store the result.

CREATE PROCEDURE CalculateTotalAmount()
    DECLARE customer_id INT;
    DECLARE total_amount DECIMAL(10, 2);

    DECLARE cur CURSOR FOR SELECT customer_id FROM Orders GROUP BY customer_id;
    OPEN cur;

    FETCH cur INTO customer_id;
    WHILE customer_id IS NOT NULL DO
        SET total_amount = 0;
        -- Calculate total amount for the current customer
        SELECT SUM(amount) INTO total_amount FROM Orders WHERE customer_id = customer_id;
        -- Store or output the result

        FETCH cur INTO customer_id;

    CLOSE cur;

In summary, a cursor in MySQL procedures is a mechanism that allows you to sequentially fetch rows from a query result within a stored procedure, making it possible to process each row individually. Cursors are useful when you need to perform complex operations on each row of a result set in procedural code.

213. What are MySQL deadlocks?

Formal Explanation: A deadlock in MySQL occurs when two or more transactions are each waiting for a resource held by the other, resulting in a circular dependency that prevents any of the transactions from proceeding. Deadlocks can lead to transactions being stuck and unable to complete, causing performance issues and database contention.

Simplified Explanation: A deadlock in MySQL is like a traffic deadlock where two cars are waiting for each other to move, but neither can move because they're blocking each other. Similarly, in a database, two transactions can be stuck waiting for resources held by each other, preventing any progress.

Detailed Explanation: Consider a scenario with two transactions: Transaction A and Transaction B, both trying to update two bank accounts concurrently. Let's assume we have two bank accounts, Account 1 and Account 2.

1. Transaction A:

UPDATE accounts SET balance = balance - 100 WHERE account_id = 1;
-- Transaction A holds a lock on Account 1

2. Transaction B:

UPDATE accounts SET balance = balance - 50 WHERE account_id = 2;
-- Transaction B holds a lock on Account 2

3. The Deadlock: Now, if both transactions continue, they will try to acquire the locks on the accounts that the other transaction holds. This creates a circular dependency and results in a deadlock.

  • Transaction A wants the lock on Account 2 held by Transaction B.

  • Transaction B wants the lock on Account 1 held by Transaction A.

Both transactions are waiting for the other to release the lock, leading to a deadlock situation. The database management system (DBMS) detects this and automatically resolves it by rolling back one of the transactions, allowing the other to proceed.

Prevention and Resolution: To prevent deadlocks, it's important to design your application and transactions in a way that minimizes the chances of circular dependencies. Properly defining the order in which locks are acquired and minimizing the time locks are held can help avoid deadlocks. In some cases, the DBMS can automatically detect and resolve deadlocks by rolling back one of the transactions.

In summary, a deadlock in MySQL occurs when two or more transactions are stuck waiting for resources held by each other, preventing any of them from progressing. Proper design and transaction management are essential to prevent and resolve deadlocks.

214. Does the order of JOINs affect the MySQL query execution plan?

#sql #middle

Yes, the order of JOINs in a MySQL query can affect the query execution plan. MySQL's query optimizer tries to find the most efficient way to retrieve data based on the query structure, table sizes, available indexes, and other factors. The order of JOINs can influence the optimizer's decision and impact the performance of the query.

Detailed Explanation: Consider two tables: orders and customers, where each order is associated with a customer using a foreign key customer_id.

1. Example with Different JOIN Order: Suppose you have the following query with two JOINs, joining orders and customers tables in different orders:

Query 1:

FROM orders 
JOIN customers ON orders.customer_id = 
JOIN products ON orders.product_id = 

Query 2:

FROM orders 
JOIN products ON orders.product_id = 
JOIN customers ON orders.customer_id = 

The order of JOINs is different between the two queries. Depending on the database statistics, indexes, and sizes of the tables, the optimizer might choose different execution plans for these queries.

2. Impact on Execution Plan: The order of JOINs can influence the optimizer's choice of using indexes, joining methods (nested loop, hash join, etc.), and filtering criteria. In some cases, one order might lead to a more efficient execution plan than the other, resulting in better query performance.

3. Query Optimization: To optimize queries with JOINs, you can consider:

  • Using appropriate indexes on columns used in JOIN and WHERE conditions.

  • Writing queries that match the expected data access patterns.

  • Analyzing query execution plans using the EXPLAIN statement to understand the chosen execution plan and make adjustments if necessary.

Conclusion: In MySQL, the order of JOINs can impact the query execution plan, affecting query performance. It's important to optimize the query, indexes, and conditions to ensure efficient execution. The MySQL query optimizer will attempt to choose the best execution plan based on various factors, including the order of JOINs.

215. You need to parse products and their prices from an online store using PHP. How would you approach this task, and what are the main considerations to take into account?

Formal Explanation: To parse products and their prices from an online store using PHP, you can utilize web scraping techniques or APIs, depending on the website's data availability and terms of use. Web scraping involves extracting data directly from the HTML of web pages, while APIs provide structured access to data. It's essential to adhere to ethical practices, respect the website's terms of use, and manage the data extraction process efficiently.

Detailed Explanation:

1. Web Scraping: Web scraping involves parsing the HTML of web pages to extract the desired information. You can use libraries like Simple HTML DOM (PHP) for this purpose. Here's a simplified example using Simple HTML DOM:

require 'simple_html_dom.php';

$url = '';
$html = file_get_html($url);

$products = [];

foreach ($html->find('div.product') as $product) {
    $name = $product->find('h2', 0)->plaintext;
    $price = $product->find('span.price', 0)->plaintext;
    $products[] = ['name' => $name, 'price' => $price];


2. API Access: Some online stores offer APIs that allow developers to fetch structured data. APIs are generally more reliable and efficient for data retrieval. Here's a hypothetical example using a RESTful API:

$apiUrl = '';
$response = file_get_contents($apiUrl);
$data = json_decode($response, true);

$products = [];

foreach ($data['products'] as $product) {
    $name = $product['name'];
    $price = $product['price'];
    $products[] = ['name' => $name, 'price' => $price];



  • Ethical Usage: Ensure that you have permission to scrape the website's data by reviewing their terms of use or using a sanctioned API.

  • Data Format: Websites may have varying structures for product information. Adjust your parsing logic accordingly.

  • Rate Limiting: Avoid sending excessive requests in a short timeframe to respect the website's server resources.

  • Error Handling: Account for scenarios where the website's structure changes or expected data is unavailable.

216. How can you implement a message queue using MySQL to store data and avoid multiple workers processing the same message?

Formal Explanation:

To create a message queue using MySQL, we first create a table in the database to store the messages. Each message has a status which is initially set to 'new'. When a worker picks up a message to process, it changes the status to 'in progress'. When it finishes processing, it sets the status to 'done'. To prevent more than one worker from processing the same message, we use a lock at the database level.

Simplified Explanations:

Think of the message queue as a real-life queue, where each person (message) waits for their turn. Some workers (processors) can attend to these people. We wouldn't want two workers attending to the same person, right? So, only the worker who speaks to the person first (get lock) can change their status (say, from 'waiting' to 'in progress'). If another worker comes, they'll know that this person is already being attended to.

Detailed Explanations in PHP Code:

Here is how a PHP script could handle this:

//Part 1: Set up your database connection
$myServer = "your_server";
$myUser = "your_user";
$myPass = "your_password";
$myDB = "your_db"; 

//establish connection to mysql
$con = new mysqli($myServer,$myUser,$myPass,$myDB);
if ($con->connect_error)  {
    die("Connection failed: " . $con->connect_error);

// Part 2: Query new messages
$sql = "SELECT id FROM messages WHERE status = 'new' LIMIT 1 FOR UPDATE;";
$result = $con->query($sql);

if ($result->num_rows > 0) {
  // Part 3: Process each new message
  while($row = $result->fetch_assoc()) {
    $id = $row["id"];

    // Let's lock this message
    $lockSql = "UPDATE messages SET status = 'in progress' WHERE id = " . $id;
    $lockResult = $con->query($lockSql);

    // Now process your message (you may want a try-catch here)
    processMessage($id); // This is your custom function to process the message

    // After processing, unlock the message
    $unlockSql = "UPDATE messages SET status = 'done' WHERE id = " . $id;
    $unlockResult = $con->query($unlockSql);
} else {
  echo "No new messages found";


function processMessage($id) {
    // Your processing logic here.

Here we're querying the database for new messages, processing them one by one, and marking them as done when processing is complete. We're locking each message before processing by setting its status to 'in progress', so no other worker can process it at the same time.

217. You have a manual for an API from the European Central Bank that provides currency exchange rates. Your task is to find the minimum and maximum exchange rates over 5 years and then break down the same information by months. How would you achieve this?

Formal Explanation: To find minimum and maximum exchange rates using the European Central Bank's API, you need to make API requests for the desired time periods, process the response data, and calculate the minimum and maximum values. Additionally, for a breakdown by months, you'll need to aggregate the data based on the month and year values from the API response.

Detailed Explanation:

1. Minimum and Maximum Rates Over 5 Years: Here's a simplified example using PHP and the cURL library to retrieve exchange rate data from the European Central Bank's API and find the minimum and maximum rates over a 5-year period:

$apiUrl = '';
$startDate = '2019-01-01';
$endDate = '2023-12-31';

$queryParams = http_build_query([
    'start_at' => $startDate,
    'end_at' => $endDate,
    'base' => 'EUR',
    'symbols' => 'USD' // Replace with desired currency code

$response = file_get_contents("$apiUrl?$queryParams");
$data = json_decode($response, true);

$rates = $data['rates'];
$minRate = min($rates);
$maxRate = max($rates);

echo "Minimum rate over 5 years: $minRate\n";
echo "Maximum rate over 5 years: $maxRate\n";

2. Monthly Breakdown: To break down rates by months, you can iterate through the rates and group them by year and month:

$monthlyRates = [];

foreach ($rates as $date => $rate) {
    $yearMonth = substr($date, 0, 7); // Extract year and month (e.g., '2022-05')
    $monthlyRates[$yearMonth][] = $rate;

foreach ($monthlyRates as $yearMonth => $rates) {
    $minRate = min($rates);
    $maxRate = max($rates);
    echo "Month: $yearMonth\n";
    echo "Minimum rate: $minRate\n";
    echo "Maximum rate: $maxRate\n\n";


  • API Limitations: Check the API documentation for rate limits and usage guidelines.

  • Currency Codes: Replace 'USD' with the desired currency code.

  • Date Ranges: Adjust the $startDate and $endDate based on your requirements.

Conclusion: To find minimum and maximum exchange rates over specified periods from the European Central Bank's API, retrieve the data, process it, and calculate the desired values. For a monthly breakdown, group rates by year and month and analyze the aggregated data. Always ensure to follow API usage guidelines and adjust the code as needed.

218. Implement a basic routing system that works according to the pattern "/{class_name}/{method_name}/".

Formal Explanation: To implement a basic routing system, you need to capture the URL, parse it to extract the class name and method name, and then invoke the appropriate method from the specified class. This can be achieved using regular expressions or URL parsing techniques.

Detailed Explanation:

Here's a simplified example of a basic routing system using PHP:

class Router {
    public function route($url) {
        $urlParts = explode('/', trim($url, '/'));

        if (count($urlParts) >= 2) {
            $className = ucfirst($urlParts[0]);
            $methodName = $urlParts[1];

            $classInstance = new $className();
            if (method_exists($classInstance, $methodName)) {
            } else {
                echo "Method not found: $methodName";
        } else {
            echo "Invalid URL format";

class UserController {
    public function index() {
        echo "User Index Page";

    public function profile() {
        echo "User Profile Page";

class ProductController {
    public function index() {
        echo "Product Index Page";

    public function detail() {
        echo "Product Detail Page";

// Usage
$router = new Router();
$router->route('/user/index');     // Output: User Index Page
$router->route('/product/detail'); // Output: Product Detail Page
$router->route('/unknown/method'); // Output: Method not found: method

In this example, the Router class parses the URL, extracts the class name and method name, and then invokes the corresponding method in the specified class. The UserController and ProductController classes define the methods that can be accessed through the routing system.


  • Security: This example is basic and lacks security measures. In a production environment, validate and sanitize the input URLs to prevent attacks.

  • Autoloading: Implement an autoloading mechanism to automatically load classes when needed.

  • Error Handling: Add proper error handling for different scenarios, such as class or method not found.

Conclusion: A basic routing system can be implemented by parsing the URL, extracting class and method names, and invoking the appropriate method. This example provides a starting point; in practice, a more advanced routing system should be used with proper security measures and error handling.

219. Write an architecture that relies on a basic abstraction. Child classes are extended using interfaces. Implement the same methods using traits (implement in the abstraction).

Create an architecture where a common set of methods is defined in an abstraction using traits. Child classes can extend these methods by implementing interfaces that extend the traits.

Detailed Explanation:

Here's an example of an architecture in PHP 8 that demonstrates the concept:

// Common traits with shared methods
trait Loggable {
    public function log($message) {
        echo "Logging: $message\n";

trait Auditable {
    public function audit($action) {
        echo "Auditing: $action\n";

// Base abstraction with shared methods
abstract class BaseService {
    use Loggable, Auditable;

    abstract public function process();

interface PaymentInterface {
    public function makePayment();

interface OrderInterface {
    public function createOrder();

// Child classes implementing interfaces
class PaymentService extends BaseService implements PaymentInterface {
    public function process() {
        echo "Processing payment...\n";

    public function makePayment() {
        echo "Payment made.\n";

class OrderService extends BaseService implements OrderInterface {
    public function process() {
        echo "Processing order...\n";

    public function createOrder() {
        echo "Order created.\n";

// Usage
$paymentService = new PaymentService();
$paymentService->process(); // Output: Processing payment...
$paymentService->log("Payment logged."); // Output: Logging: Payment logged.
$paymentService->makePayment(); // Output: Payment made.

$orderService = new OrderService();
$orderService->process(); // Output: Processing order...
$orderService->log("Order logged."); // Output: Logging: Order logged.
$orderService->audit("Order created."); // Output: Auditing: Order created.
$orderService->createOrder(); // Output: Order created.

In this example, we have defined common methods in traits (Loggable and Auditable). The BaseService abstract class uses these traits and provides an abstract process() method. We then define interfaces (PaymentInterface and OrderInterface) that can be implemented by child classes.

The PaymentService and OrderService classes implement the respective interfaces and provide concrete implementations for the process() and other methods.


  • This example is a demonstration of the architecture concept. In real-world applications, you might need to handle dependency injection, error handling, and other considerations.

  • Traits and interfaces can be used to compose shared functionality while providing flexibility for customization in different classes.

Conclusion: By using traits to share methods and interfaces to extend shared functionality, you can create an architecture that allows for code reuse and customization across different classes. This approach promotes modular design and efficient development.

220. Write a query that will output the "id" and "val" values. If the value of the "column" column is greater than 5, the "val" should be "val1"; otherwise, it should be "val2".

Compose an SQL query that selects the "id" and calculated "val" columns from a table. If the value of the "column" column is greater than 5, set the "val" column to "val1"; otherwise, set it to "val2".

Detailed Explanation:

Let's assume we have a table named "data" with columns "id", "column", and "val". We want to retrieve the "id" and calculate the "val" column based on the condition.

-- SQL Query
       CASE WHEN column > 5 THEN 'val1' ELSE 'val2' END AS val 
  FROM data;

Here's how the PHP code might look when using PDO to execute the SQL query:

// Create a PDO connection
$dsn = "mysql:host=localhost;dbname=your_database";
$user = "your_username";
$password = "your_password";
$dbh = new PDO($dsn, $user, $password);

// SQL query
$sql = "SELECT id, 
               CASE WHEN column > 5 THEN 'val1' ELSE 'val2' END AS val 
          FROM data";

// Prepare and execute the query
$stmt = $dbh->prepare($sql);

// Fetch results
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Output results
foreach ($results as $row) {
    echo "id: " . $row['id'] . ", val: " . $row['val'] . "\n";

// Close the connection
$dbh = null;

In this example, the SQL query uses the CASE statement to determine whether the value of the "column" column is greater than 5. If it is, the "val" is set to "val1"; otherwise, it's set to "val2". The PHP code executes the query using PDO and outputs the results.


  • This example demonstrates using PDO for database access. You can adapt it to use other database libraries if needed.

  • Ensure you have proper error handling and sanitation in a production environment.

Conclusion: By using SQL's CASE statement and PDO in PHP, you can achieve the desired output of the "id" and calculated "val" values based on the specified condition. This approach allows you to dynamically generate values in the result set based on certain conditions.

221. Write a custom Laravel Artisan command that will output the current time to the console

To create a custom Laravel Artisan command, follow these steps:

  1. Open your terminal and navigate to your Laravel project directory.

  2. Use the make:command Artisan command to generate a new custom command:

     php artisan make:command ShowTime
  3. This will create a new command class in the app/Console/Commands directory. Open the generated file, which will be named ShowTime.php.

  4. Modify the generated command class to output the current time:

     // app/Console/Commands/ShowTime.php
     namespace App\Console\Commands;
     use Illuminate\Console\Command;
     class ShowTime extends Command
         protected $signature = 'show:time';
         protected $description = 'Display the current time';
         public function __construct()
         public function handle()
             $currentTime = now()->toTimeString(); // Get the current time
             $this->info("Current time: {$currentTime}");
  5. Now, you can run your custom command in the console:

     php artisan show:time

    This will output the current time to the console.


  • This example uses Laravel's built-in now() function to get the current time. You can adjust the time format if needed.

  • Customize the command's signature and description according to your preference.

Conclusion: Creating a custom Laravel Artisan command is a straightforward process. You can generate a new command using make:command, modify its logic in the handle method, and then execute the command using php artisan. This allows you to add custom functionality and interact with your Laravel application from the command line.

222. How can you access the value of a private property of a class at runtime without using reflection and without using a getter method?

Formal Explanation:

Normally, private properties in a class are not accessible outside the class. If the class itself doesn't provide a method to access these private properties and if we don't want to use reflection, we can use a workaround like using a closure bound to the object.

Simplified Explanations:

We can use a trick with a closure to get hold of the object scope, allowing us to see private properties. Essentially, we create a function that has access to the object's scope and use that to return a private property.

Detailed Explanation with PHP Code Example:

Here is an example PHP snippet:

class MyClass
    private $privateProperty = "secret";

$obj = new MyClass();

$accessPrivateProperty = function() {
    return $this->privateProperty;

$accessor = $accessPrivateProperty->bindTo($obj, 'MyClass');
echo $accessor();  // Outputs: secret

In the code above, we use PHP's Closure::bindTo() method, which duplicates the closure with a new bound object and class scope, and then returns the new closure. We bind our $accessPrivateProperty closure to the instance $obj of MyClass, thus gaining access to the private property $privateProperty.

Still, it's essential to respect the principle of encapsulation in Object Oriented Programming (OOP). Getting direct access to class private properties outside of it is considered a bad practice. It can be used for debugging purposes or when dealing legacy code which cannot be refactored.

223. Should we pass null as a parameter to methods? If not, why? And how should we write code?

As a good practice in object-oriented programming and clean code principles, passing null as a parameter to a method is generally discouraged. This is because it can make the code less readable and more error-prone as it requires additional null checks inside the method.

Instead of passing null as a parameter, we can use method overloading (if the language supports it), optional parameters, or the Null Object Pattern.

Simplified Explanations:

Instead of passing null as a parameter, you can:

  1. Make the parameter optional

  2. Use different methods for different situations. For example, instead of using one save method that can accept null, you might have a separate create and update method.

Detailed Explanation:

Let's consider a simple function that could receive a null as a parameter:

function addStudent($name = null)
    if ($name === null) {
        throw new Exception("Name must not be null");

    // Add student

We can improve it by removing the possibility of null:

function addStudent($name)
    // Add student

With this version, if we try to call addStudent(null), we'll get a helpful error message indicating that we're using the function incorrectly. Our code is now clearer and any bugs related to passing null will be easier to spot.

Additionally, in PHP 7.1 and up, we can use nullable types to signify that a value can be null:

function addStudent(?string $name)
    // If name is null, assign a default value
    $name = $name ?? 'default name';

    // Add student

This way, the function communicates that it can accept nulls, and we directly handle it, improving the readability and robustness of the code.

224. Tell me about ReactPHP or Swoole.

ReactPHP is a powerful asynchronous event-driven framework for PHP. It enables building non-blocking applications using the event loop pattern. Here's a simple example of using ReactPHP to create an HTTP server:

require 'vendor/autoload.php';

use React\Http\Server;
use React\Http\Response;
use Psr\Http\Message\ServerRequestInterface;

$loop = React\EventLoop\Factory::create();
$server = new Server(function (ServerRequestInterface $request) {
    return new Response(200, ['Content-Type' => 'text/plain'], "Hello, ReactPHP!\n");

$socket = new React\Socket\Server(8080, $loop);


Swoole is an event-driven, high-performance networking communication framework for PHP. It's designed for creating long-running, highly concurrent, and asynchronous applications. Here's a simple example of using Swoole to create an HTTP server:

$http = new Swoole\Http\Server("", 8080);

$http->on("request", function ($request, $response) {
    $response->header("Content-Type", "text/plain");
    $response->end("Hello, Swoole!\n");


Both ReactPHP and Swoole allow you to build applications that can handle many concurrent connections without blocking, making them suitable for tasks such as real-time applications, APIs, and microservices.

Pros and Cons:

ReactPHP: Pros:

  • Mature and well-established asynchronous framework.

  • Used for building scalable, non-blocking applications.

  • Comes with various components for different purposes.


  • Learning curve for newcomers to asynchronous programming.

  • Requires understanding event loops and callback patterns.

Swoole: Pros:

  • Offers a range of features beyond networking, including coroutines, timers, and more.

  • Provides better performance in some use cases due to its tightly integrated nature.


  • Swoole might be overkill for smaller projects or those not requiring asynchronous programming.

  • Some PHP developers might be less familiar with Swoole compared to traditional PHP frameworks.

Conclusion: Both ReactPHP and Swoole are powerful tools for building asynchronous and event-driven applications in PHP. They allow developers to create highly concurrent applications that can handle many connections simultaneously. Depending on your project's requirements and your familiarity with asynchronous programming, you can choose the framework that best suits your needs.

225. What is sensitive data? How are they stored in the database? How are they displayed in logs? What appeared in PHP to hide the output of this data in debug messages?

Formal Explanation:

Sensitive data is information that must be protected from unauthorized access to safeguard privacy or security, such as passwords, credit card numbers, health details, and social security numbers.

In databases, sensitive data should be stored in an encrypted or hashed form. When displayed in logs, sensitive data should be either masked or completely omitted to prevent unintended exposure.

Since version 7.4, PHP introduced the concept of typed properties, which can be used along with custom getter and setter methods to control access and visualization of sensitive data. The __debugInfo() method can also be overridden to control the output when an object is printed out with var_dump().

And starting from PHP 8.2, a new feature had been introduced called "Sensitive", which automatically redacts the sensitive information from stack traces whenever an exception is thrown. By declaratively marking a parameter as "Sensitive", it helps ensure sensitive information doesn't make its way into logs unintentionally.

Detailed Explanation:

Here's how you might handle sensitive data when setting a property:

class User
    private $password;  // sensitive data

    public function setPassword($password)  // setter with hash
        $this->password = password_hash($password, PASSWORD_BCRYPT);

    public function getPassword()  // getter
        return '****'; // never display plain password!

    public function __debugInfo()  // avoid sensitive data in var_dump
        return [
            'password' => $this->getPassword(),

$user = new User();

var_dump($user);  // password will be '****'

This example sets sensitive data using the setPassword method that automatically hashes the password. When getting this property (or using var_dump), we ensure that the sensitive data is not displayed.

Here's how you might declare a function with a sensitive parameter using PHP 8.2:

function login(string $username, #[Sensitive] string $password) 
    //handling login

try {
    login("username", "password");
} catch (TypeError $e) {

In this example, should a TypeError occur during the call to login(), the $password parameter marked as #[Sensitive] will be redacted from the stack trace, ensuring that its value isn't accidentally logged. When attempting to log the error trace, the sensitive parameter value is replaced with a '[redacted]' string, helping prevent accidental leakage of sensitive information in your logs.

Previous articles of the series:

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 1-15.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 16-30.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 31-45.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 46-60.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 61-75.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 91-105.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 106-120.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 121-135.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 136-150.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 151-165.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 166-180.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 181-195.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 196-210.