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PHP Learning Path Beginner to Advanced

A comprehensive guide to mastering PHP with focus on interview-critical concepts.

Table of Content

1. Getting Started with PHP Basics

2. Control Structures

3. Functions and Error Handling

4. Working with Forms

5. Object-Oriented PHP

6. Database Interaction

7. Security Practices

8. Advanced Concepts

9. Frameworks and Tools

10. PHP Internals

11. Best Practices

12. Interview Preparation

13. Projects and Practice

14. Resources

1. Getting Started with PHP Basics

PHP Environment Setup

To start coding in PHP, you need a local development environment. Popular options include:

  1. XAMPP: A complete package with Apache, MySQL, and PHP.
  2. WAMP: Similar to XAMPP but for Windows.
  3. Docker: A containerized environment for consistent development.
<?php
phpinfo(); // Displays PHP configuration details
?>

Basic Syntax and Tags

PHP code is embedded within <?php and ?> tags. Example:

<?php
echo "Hello, World!";
?>

Variables and Constants

Data Types

PHP supports:

int

Integers are whole numbers (positive/negative) without decimals. PHP uses 32/64-bit integers depending on the system.

<?php
$a = 42;        // Decimal
$b = 0x1A;      // Hexadecimal (26)
$c = 0b1010;    // Binary (10)
$d = 0755;      // Octal (493)
?>

Tricky Question: Q: “Why does (int) '08' return 0 instead of 8?” A: PHP parses numbers starting with 0 as octal, but 8 is invalid in octal (digits 0-7). Use (int) '8' or intval('08', 10).

float

Floating-point numbers (decimals). Caution: Precision issues due to binary representation.

<?php
$a = 1.234;
$b = 10.0;      // Float, not integer!
$c = 2.5e3;     // 2500
?>

Tricky Question: Q: “Why does 0.1 + 0.2 === 0.3 return false?” A: Floating-point precision errors. Use abs(0.1 + 0.2 - 0.3) < 1e-9 or bcadd() for exact comparisons.

string

Textual data. Supports single quotes (no variable parsing) and double quotes (variable parsing).

<?php
$name = "Alice";
echo 'Hello, $name';    // Outputs "Hello, $name"
echo "Hello, $name";    // Outputs "Hello, Alice"
?>

Tricky Question: Q: “What is the output of echo '5' + '2'?” A: 7 (PHP performs type juggling and converts strings to integers).

bool

Boolean (true/false). Falsy values: 0, "", null, empty arrays.

<?php
$isAdmin = true;
if ("0") {  // Evaluates to false (string "0" is falsy)
    // Won't execute
}
?>

Tricky Question: Q: “Is 'false' considered true or false?” A: true—non-empty strings are truthy, even if the content is “false”.

array

Ordered maps with key-value pairs.

Types of Array in PHP

  1. Indexed Array:

    $arr = ["Apple", "Banana", "Cherry"];
echo $arr[0]; // Apple

  2. Associative Array:

    $user = ["name" => "John", "age" => 25];
echo $user["name"]; // John

  3. Multidimensional Array:

    $store = [
    "fruits" => ["Apple", "Banana"],
    "vegetables" => ["Carrot", "Spinach"]
];
echo $store["fruits"][1]; // Banana

Tricky Question: Q: “What happens if you use array_push($arr, $item) vs $arr[] = $item?” A: Both add elements, but array_push() incurs function call overhead. Use [] for single elements.

object

Instances of classes. Use stdClass for generic objects.

<?php
class User {}
$user = new User();
$user->name = "Alice";

$obj = (object) ["id" => 1]; // Cast array to object
?>

Tricky Question: Q: “How are objects passed to functions in PHP?” A: By reference (but explicit cloning is needed to create copies).

null

Represents “no value”. Variables are null if unset or assigned null.

<?php
$x = null;
if (is_null($x)) {
    echo "x is null";
}
?>

Tricky Question: Q: “What’s the difference between isset($var) and !is_null($var)?” A: isset() checks if a variable exists and is not null. !is_null() throws a warning if the variable doesn’t exist.

resource

Special variables holding references to external resources (e.g., files, databases).

<?php
$file = fopen("test.txt", "r"); // Returns a file resource
?>

Tricky Question: Q: “What happens if you serialize a resource?” A: Serialization fails—resources can’t be serialized as they’re pointers to external states.

Key Takeaways for Interviews:

  1. Weak Typing: PHP converts types implicitly (e.g., "5" → 5 in arithmetic).
  2. Array Flexibility: Arrays can act as lists, dictionaries, stacks, etc.
  3. Null Handling: Use === null for strict checks.
  4. Resource Limitations: Resources are temporary handles (e.g., database connections must be closed explicitly).

Type Juggling and Type Casting

Language Constructs in PHP

Language constructs in PHP are built-in functions or statements that do not require parentheses (although they can be used with them). These constructs behave like functions but are part of PHP’s core syntax.

Types of Language Constructs in PHP

Language constructs fall under different categories based on their functionality.

1. Variable and Type Handling Constructs

Construct Description
isset() Returns true if a variable is set and not NULL
unset() Destroys a variable
empty() Returns true if a variable is empty (0, "", NULL, false, [])
die() or exit() Terminates the script execution
eval() Executes a string as PHP code

2. Output and Debugging Constructs

Construct Description
echo Outputs one or more strings (faster than print)
print Outputs a string (returns 1, unlike echo)
print_r() Prints human-readable information about a variable
var_dump() Dumps detailed information about a variable
var_export() Outputs a parsable string representation of a variable

3. Control Structures (Conditional & Loop Constructs)

Construct Description
if, else, elseif Conditional statements
switch, case, default Multi-way conditional statement
while, do-while Looping constructs
for, foreach Iteration constructs
break Exits the current loop
continue Skips the current loop iteration
return Returns a value from a function

4. Function and Class Handling Constructs

Construct Description
function Defines a function
global Declares global variables inside functions
static Declares static variables inside functions
use Imports namespaces or traits in PHP
class, interface, trait Defines object-oriented components
extends, implements Establishes inheritance in classes
abstract, final Defines class behavior
clone Creates a copy of an object

5. File and Directory Constructs

Construct Description
include Includes and executes a file (produces a warning if the file is missing)
require Includes and executes a file (produces a fatal error if the file is missing)
include_once Ensures a file is included only once
require_once Ensures a file is required only once

6. Exception Handling Constructs

Construct Description
try, catch, finally Exception handling mechanism
throw Throws an exception

7. Miscellaneous Constructs

Construct Description
list() Assigns variables from an array
array() Creates an array (alternative to [])
isset() Checks if a variable is set
unset() Unsets a variable
declare() Sets execution directives (used with ticks)
goto Jumps to a specific label in the script (not recommended)

Why Are Language Constructs Different from Functions?

Conclusion

  1. PHP has several language constructs grouped under control structures, file handling, function handling, output handling, and more.
  2. Unlike functions, language constructs do not always require parentheses.

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2. Control Structures

Conditional Statements

if ($age > 18) {
    echo "Adult";
} else {
    echo "Minor";
}

Looping Structures

break/continue Statements

Alternative Syntax for Control Structures

Use : and end for cleaner control structures in templates:

<?php if ($loggedIn): ?>
    <p>Welcome back!</p>
<?php endif; ?>

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3. Functions and Error Handling

Function Declaration and Arguments

Define functions with the function keyword:

function greet($name) {
    return "Hello, $name!";
}

Return Types and Type Declarations

Specify return types for type safety:

function add(int $a, int $b): int {
    return $a + $b;
}

Variable Scope

Types of Function Calls in PHP

1. Call by Value (Default Behavior)

Example:

<?php
function callByValue($num) {
    $num += 10;  // Modify the local copy
    echo "Inside function: $num\n";
}

$value = 20;
callByValue($value);
echo "Outside function: $value\n"; // Original value remains unchanged
?>

Output:

Inside function: 30
Outside function: 20

📌 Explanation: The function receives a copy of $value, so modifying it inside does not change the original $value.

2. Call by Reference

Example:

<?php
function callByReference(&$num) {
    $num += 10;  // Modify the original variable
    echo "Inside function: $num\n";
}

$value = 20;
callByReference($value);
echo "Outside function: $value\n"; // Original value is changed
?>

Output:

Inside function: 30
Outside function: 30

📌 Explanation: Since we used &$num, the function modifies the actual $value, not a copy.

Global Scope

<?php

// Using Global Variable
$globalNum = 50;

function usingGlobal() {
    global $globalNum; // Access the global variable
    $globalNum += 20;
    echo "Inside usingGlobal: $globalNum<br>";
}

// Static Variable Example
function staticExample() {
    static $count = 0; // Static variable retains value across function calls
    $count++;
    echo "Static count: $count<br>";
}

usingGlobal();
echo "Outside usingGlobal: $globalNum<br><br>";

staticExample();
staticExample();
staticExample();
?>

Answer

Inside usingGlobal: 70
Outside usingGlobal: 70

Static count: 1
Static count: 2
Static count: 3

Default Argument Value

Example:

<?php
function greet($name = "Guest") {
    echo "Hello, $name!\n";
}

greet();          // Uses default value "Guest"
greet("Manish");  // Overrides default value
?>

Output:

Hello, Guest!
Hello, Manish!

📌 Explanation: If no argument is passed, "Guest" is used as the default value.

4. Type Hinting

Example:

<?php
function sum(int $a, int $b) {
    return $a + $b;
}

echo sum(5, 10);   // Works fine
echo sum("5", "10"); // Works, as PHP auto-converts strings to int
// echo sum("five", "ten"); // Fatal error!
?>

📌 Explanation:

Conclusion

The function call on line 8 is Call by Value, as arguments are passed without a reference (&). You can change it to Call by Reference by adding & before the parameters in the function definition.

Error Types

Error Handling

Use try/catch for exceptions:

try {
    // Code that may throw an exception
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

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4. Working with Forms

$_GET and $_POST Superglobals

$_GET: Retrieve Data from URL Parameters

$_GET is used to collect data sent via URL parameters (query strings). It is commonly used for search forms or pagination.

Example:

// URL: http://example.com/?name=John&age=25
if (isset($_GET['name']) && isset($_GET['age'])) {
    $name = $_GET['name']; // John
    $age = $_GET['age'];   // 25
    echo "Name: $name, Age: $age";
}

Key Points:

$_POST: Retrieve Data from Form Submissions

$_POST is used to collect data sent via HTTP POST requests, typically from HTML forms. It is more secure than $_GET for sensitive data.

Example:

// HTML Form
<form method="POST" action="process.php">
    <input type="text" name="username">
    <input type="password" name="password">
    <button type="submit">Submit</button>
</form>

// process.php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    $password = $_POST['password'];
    echo "Username: $username, Password: $password";
}

Key Points:

Form Validation and Sanitization

Form validation ensures that user inputs meet specific criteria, while sanitization cleans the data to prevent security risks like XSS (Cross-Site Scripting).

Example:

$errors = [];

// Validate and sanitize input
if (empty($_POST['name'])) {
    $errors[] = "Name is required.";
} else {
    $name = htmlspecialchars($_POST['name']); // Sanitize input
}

if (empty($_POST['email'])) {
    $errors[] = "Email is required.";
} elseif (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
    $errors[] = "Invalid email format.";
} else {
    $email = filter_var($_POST['email'], FILTER_SANITIZE_EMAIL); // Sanitize email
}

if (empty($errors)) {
    echo "Name: $name, Email: $email";
} else {
    foreach ($errors as $error) {
        echo "<p>$error</p>";
    }
}

Key Points:

File Uploads Handling

PHP uses the $_FILES superglobal to handle file uploads. It provides information about the uploaded file, such as its name, size, and temporary location.

Example:

if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_FILES['file'])) {
    $file = $_FILES['file'];

    // Check for errors
    if ($file['error'] === UPLOAD_ERR_OK) {
        $uploadDir = 'uploads/';
        $uploadPath = $uploadDir . basename($file['name']);

        // Move the file to the upload directory
        if (move_uploaded_file($file['tmp_name'], $uploadPath)) {
            echo "File uploaded successfully!";
        } else {
            echo "Failed to move the file.";
        }
    } else {
        echo "Error during file upload.";
    }
}

Key Points:

CSRF Protection Basics

CSRF (Cross-Site Request Forgery) attacks trick users into performing actions they didn’t intend to. To prevent this, use CSRF tokens.

Example:

// Generate a CSRF token
session_start();
if (empty($_SESSION['csrf_token'])) {
    $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
}

// HTML Form
<form method="POST" action="process.php">
    <input type="hidden" name="csrf_token" value="<?php echo $_SESSION['csrf_token']; ?>">
    <input type="text" name="username">
    <button type="submit">Submit</button>
</form>

// process.php
session_start();
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    if (!isset($_POST['csrf_token']) || $_POST['csrf_token'] !== $_SESSION['csrf_token']) {
        die("CSRF token validation failed.");
    }
    // Process the form data
    echo "Form submitted successfully!";
}

Key Points:

Summary of Key Concepts:

  1. $_GET: Use for non-sensitive data passed via URLs.
  2. $_POST: Use for sensitive data submitted via forms.
  3. Form Validation and Sanitization: Ensure data is clean and valid.
  4. File Uploads: Handle files securely using $_FILES.
  5. CSRF Protection: Use tokens to prevent unauthorized form submissions.

These topics are critical for PHP interviews and real-world applications. Practice these concepts with code examples to solidify your understanding!

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5. Object-Oriented PHP

1. Classes and Objects

Class

A class is a blueprint for creating objects. It defines properties (variables) and methods (functions) that the objects will have.

Object

An object is an instance of a class. It can access the properties and methods defined in the class.

class Car {
    // Property
    public $model;

    // Method
    public function startEngine() {
        return "Engine started!";
    }
}

// Create an object
$tesla = new Car();
$tesla->model = "Model S";
echo $tesla->startEngine(); // Output: Engine started!

Key Points for Interviews:

2. Properties and Methods

Properties

Variables declared inside a class. They hold the object’s state.

Methods

Functions declared inside a class. They define the object’s behavior.

class BankAccount {
    // Property (with visibility)
    private $balance = 0;

    // Method to modify property
    public function deposit($amount) {
        $this->balance += $amount;
    }

    public function getBalance() {
        return $this->balance;
    }
}

$account = new BankAccount();
$account->deposit(100);
echo $account->getBalance(); // Output: 100

Key Points:

3. Inheritance and Polymorphism

Inheritance

A child class inherits properties and methods from a parent class.

Polymorphism

Child classes can override parent methods to provide specific implementations.

class Vehicle {
    public function start() {
        return "Vehicle started!";
    }
}

class Car extends Vehicle {
    // Override parent method
    public function start() {
        return "Car engine started!";
    }
}

$vehicle = new Vehicle();
echo $vehicle->start(); // Output: Vehicle started!

$car = new Car();
echo $car->start(); // Output: Car engine started!

Interview Tip:

4. Magic Methods

Magic methods in PHP are special methods that begin with double underscores (__) and allow you to control various behaviors of your objects. Many of these methods interact with the properties of your object—whether to initialize them, control access, or modify them during serialization. Below is a list of key magic methods, their purposes, and code examples.

1. __construct and __destruct

Example:

<?php
class MagicDemo {
    public $data;

    public function __construct() {
        echo "__construct called\n";
        // Initialize object properties
        $this->data = ['name' => 'MagicDemo', 'version' => '1.0'];
    }

    public function __destruct() {
        echo "__destruct called\n";
    }
}

$demo = new MagicDemo();
?>

##—

2. __get, __set, __isset, and __unset

These methods control access to inaccessible or non-existing properties.

Example:

<?php
class MagicProperties {
    // Private property to store data
    private $data = [];

    public function __get($name) {
        echo "__get: accessing '$name'\n";
        return isset($this->data[$name]) ? $this->data[$name] : null;
    }

    public function __set($name, $value) {
        echo "__set: setting '$name' to '$value'\n";
        $this->data[$name] = $value;
    }

    public function __isset($name) {
        echo "__isset: checking if '$name' is set\n";
        return isset($this->data[$name]);
    }

    public function __unset($name) {
        echo "__unset: unsetting '$name'\n";
        unset($this->data[$name]);
    }
}

$obj = new MagicProperties();
$obj->name = "PHP Magic";   // Calls __set
echo $obj->name . "\n";       // Calls __get
if (isset($obj->name)) {      // Calls __isset
    echo "Property 'name' is set\n";
}
unset($obj->name);           // Calls __unset
?>

3. __call and __callStatic

Example:

<?php
class MagicMethodCalls {
    public function __call($name, $arguments) {
        echo "__call: Attempt to call instance method '$name' with arguments: " . implode(', ', $arguments) . "\n";
    }

    public static function __callStatic($name, $arguments) {
        echo "__callStatic: Attempt to call static method '$name' with arguments: " . implode(', ', $arguments) . "\n";
    }
}

$obj = new MagicMethodCalls();
$obj->nonExistentMethod("arg1", "arg2");   // Triggers __call
MagicMethodCalls::nonExistentStatic("staticArg");  // Triggers __callStatic
?>

4. __sleep and __wakeup

These methods handle the serialization and unserialization of objects.

Example:

<?php
class SerializableDemo {
    public $data = "Some data";
    private $tempResource;

    public function __sleep() {
        echo "__sleep called\n";
        // Return only the properties you wish to serialize
        return ['data'];
    }

    public function __wakeup() {
        echo "__wakeup called\n";
        // Reinitialize properties or resources (e.g., database connection)
        $this->tempResource = "Reinitialized resource";
    }
}

$object = new SerializableDemo();
$serialized = serialize($object);  // Triggers __sleep
$unserialized = unserialize($serialized);  // Triggers __wakeup
?>

5. __toString

Allows an object to be treated as a string. This method must return a string.

Example:

<?php
class Stringable {
    private $data = ['name' => 'Stringable Demo', 'version' => '2.0'];

    public function __toString() {
        return "__toString: " . json_encode($this->data);
    }
}

$obj = new Stringable();
echo $obj;  // Automatically calls __toString
?>

6. __invoke

Invoked when an object is called as a function.

Example:

<?php
class CallableDemo {
    public function __invoke(...$args) {
        echo "__invoke called with arguments: " . implode(', ', $args) . "\n";
    }
}

$obj = new CallableDemo();
$obj("first", "second");  // Treats $obj as a function, calling __invoke
?>

7. __set_state

Called when the object is exported with var_export(). It allows the recreation of an object with the given state.

Example:

<?php
class StateDemo {
    public $data;

    public function __construct($data = null) {
        $this->data = $data;
    }

    public static function __set_state($array) {
        echo "__set_state called\n";
        $obj = new self();
        $obj->data = $array['data'];
        return $obj;
    }
}

$state = var_export(new StateDemo("test state"), true);
echo $state;
?>

8. __clone

Invoked when an object is cloned using the clone keyword. It is useful for performing deep copies or resetting properties.

Example:

<?php
class CloneDemo {
    public $data;

    public function __construct($data) {
        $this->data = $data;
    }

    public function __clone() {
        echo "__clone called\n";
        // Example: reset a property after cloning
        $this->data = "Cloned: " . $this->data;
    }
}

$original = new CloneDemo("Original Data");
$cloned = clone $original;
echo $cloned->data;  // Output includes the modification from __clone
?>

9. __debugInfo

Controls what information is shown when using debugging functions like var_dump().

Example:

<?php
class DebugDemo {
    private $data = "Secret Data";
    private $hidden = "Hidden Info";

    public function __debugInfo() {
        return [
            'data' => $this->data,
            // 'hidden' is omitted from the debug info
        ];
    }
}

$obj = new DebugDemo();
var_dump($obj);  // Only shows 'data' property
?>

10. __serialize and __unserialize (PHP 7.4+)

Newer magic methods for serialization that offer more control than __sleep and __wakeup.

Example:

<?php
class NewSerializableDemo {
    private $data;
    private $tempResource;

    public function __construct($data) {
        $this->data = $data;
        $this->tempResource = "Resource";
    }

    public function __serialize(): array {
        echo "__serialize called\n";
        return ['data' => $this->data];
    }

    public function __unserialize(array $data): void {
        echo "__unserialize called\n";
        $this->data = $data['data'];
        $this->tempResource = "Reinitialized Resource";
    }
}

$obj = new NewSerializableDemo("New Data");
$serialized = serialize($obj);  // Uses __serialize
$unserialized = unserialize($serialized);  // Uses __unserialize
?>

Interview Question:

5. Interfaces vs Abstract Classes

Interfaces

Abstract Classes

// Interface
interface Movable {
    public function move();
}

// Abstract Class
abstract class Animal {
    abstract public function makeSound(); // Must be implemented
    public function eat() {
        echo "Eating...";
    }
}

class Dog extends Animal implements Movable {
    public function makeSound() {
        echo "Woof!";
    }
    public function move() {
        echo "Dog is running!";
    }
}

$dog = new Dog();
$dog->move(); // Output: Dog is running!

Key Differences:

  Interface Abstract Class
Implementation Only method signatures Partial implementation allowed
Inheritance Multiple interfaces Single abstract class

6. Traits and Namespaces

Traits

Reusable code units that solve single inheritance limitations.

trait Loggable {
    public function log($message) {
        echo "Log: $message";
    }
}

class User {
    use Loggable; // Include the trait
}

$user = new User();
$user->log("User created"); // Output: Log: User created

Namespaces

Organize code and prevent naming collisions.

namespace Database;

class Connection {
    public function connect() {
        return "Connected to DB!";
    }
}

// Usage
$conn = new \Database\Connection();
echo $conn->connect(); // Output: Connected to DB!

Interview Tip:

7. Autoloading (PSR-4)

Automatically load classes without require statements.

Step 1: Directory Structure

src/
└── Models/
    └── User.php

Step 2: composer.json

{
  "autoload": {
    "psr-4": {
      "App\\": "src/"
    }
  }
}

Step 3: Class Definition

// src/Models/User.php
namespace App\Models;

class User {
    public function __construct() {
        echo "User loaded!";
    }
}

Step 4: Usage

require 'vendor/autoload.php';

$user = new \App\Models\User(); // Output: User loaded!

Interview Question:

💡 Key OOP Interview Topics

  1. Encapsulation: Hide internal state using private/protected properties.
  2. Abstraction: Simplify complexity using interfaces/abstract classes.
  3. Composition over Inheritance: Favor object composition for flexibility.
  4. Dependency Injection: Pass dependencies to objects instead of hardcoding.
// Dependency Injection Example
class Logger {
    public function log($message) {
        echo $message;
    }
}

class UserService {
    private $logger;

    public function __construct(Logger $logger) {
        $this->logger = $logger;
    }
}

$logger = new Logger();
$userService = new UserService($logger);

📚 Resources

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6. Database Interaction

MySQLi vs PDO

MySQLi

MySQL-specific extension for interacting with MySQL databases.

// MySQLi Connection
$mysqli = new mysqli("localhost", "user", "password", "database");
if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

PDO (PHP Data Objects)

Database-agnostic extension supporting 12+ databases (MySQL, PostgreSQL, SQLite, etc.).

// PDO Connection
try {
    $pdo = new PDO("mysql:host=localhost;dbname=database", "user", "password");
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    die("Connection failed: " . $e->getMessage());
}

Key Differences:

Feature MySQLi PDO
Database Support MySQL only Multiple databases
Prepared Statements Procedural & Object-oriented Object-oriented only
Error Handling Limited Exceptions & error codes

Prepared Statements

Prevent SQL injection by separating SQL logic from data.

Example with MySQLi:

$stmt = $mysqli->prepare("SELECT * FROM users WHERE email = ?");
$stmt->bind_param("s", $email); // "s" = string type
$stmt->execute();
$result = $stmt->get_result();

Example with PDO:

$stmt = $pdo->prepare("SELECT * FROM users WHERE id = :id");
$stmt->execute([':id' => $id]);
$user = $stmt->fetch(PDO::FETCH_ASSOC);

Interview Tip:

Transactions and Error Handling

Ensure atomicity for multiple database operations.

try {
    $pdo->beginTransaction();

    // Transfer $100 from Alice to Bob
    $pdo->exec("UPDATE accounts SET balance = balance - 100 WHERE user = 'Alice'");
    $pdo->exec("UPDATE accounts SET balance = balance + 100 WHERE user = 'Bob'");

    $pdo->commit();
} catch (Exception $e) {
    $pdo->rollBack();
    echo "Transaction failed: " . $e->getMessage();
}

Key Points:

ORM Basics

Object-Relational Mapping (ORM) maps database tables to PHP objects.

Example with Eloquent (Laravel):

// Define a Model
class User extends Illuminate\Database\Eloquent\Model {
    protected $table = 'users';
}

// Fetch a user
$user = User::find(1);
echo $user->name;

// Create a user
User::create(['name' => 'Alice', 'email' => 'alice@example.com']);

Popular ORMs:

Advantages:

Database Design Patterns

Active Record Pattern

Objects carry data and database access logic.

class User {
    public $id;
    public $name;

    public function save() {
        // Save to database
    }
}

Repository Pattern

Separates data access logic from business logic.

class UserRepository {
    public function findById($id) {
        // Fetch user from DB
    }

    public function save(User $user) {
        // Save user to DB
    }
}

Comparison:

Pattern Use Case
Active Record Simple apps with direct DB access
Repository Complex apps with layered architecture

💡 Key Interview Questions

  1. Q: Why use PDO over MySQLi?A: PDO supports multiple databases and provides better error handling.
  2. Q: How do transactions prevent data corruption?A: They ensure all operations succeed or fail together.
  3. Q: What is the N+1 problem in ORM? A: Excessive queries due to lazy loading (fix: eager loading).

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7. Security Practices

SQL Injection Prevention

Use prepared statements and parameterized queries.

XSS Prevention and Output Escaping

Escape output using htmlspecialchars().

Password Hashing

Hash passwords with password_hash() and verify with password_verify().

Session Security

Regenerate session IDs and use secure cookies.

HTTPS and Secure Cookies

Enforce HTTPS and set cookie flags like Secure and HttpOnly.

CORS and CSRF Protection

Implement CORS headers and CSRF tokens.

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8. Advanced Concepts

Composer and Dependency Management

Manage dependencies using Composer.

MVC Architecture Pattern

Build applications using Model-View-Controller.

RESTful API Development

Create REST APIs with proper HTTP methods and status codes.

Middleware and Routing

Implement middleware and routing in frameworks.

Caching Strategies

Use OPcache, Redis, and other caching tools.

PHP-FPM and Performance Tuning

Optimize PHP performance with PHP-FPM.

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9. Frameworks and Tools

Laravel Fundamentals

Learn Laravel’s Eloquent ORM, Blade templating, and Artisan CLI.

Symfony Components

Use Symfony components like HttpFoundation and DependencyInjection.

Testing (PHPUnit, Pest)

Write tests with PHPUnit and Pest.

Debugging (Xdebug, Ray)

Debug applications with Xdebug and Ray.

Deployment Strategies

Deploy PHP applications using CI/CD pipelines.

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10. PHP Internals

Zend Engine Basics

Understand the core of PHP’s execution engine.

Memory Management

Learn how PHP manages memory allocation.

Opcode Caching

Use OPcache to improve performance.

Garbage Collection

Understand PHP’s garbage collection mechanism.

PHP Lifecycle

Explore the lifecycle of a PHP request.

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11. Best Practices

PSR Standards

Follow PSR-1, PSR-12, and other coding standards.

SOLID Principles

  1. S - Single Responsibility Principle
  2. O - Open/Closed Principle
  3. L - Liskov Substitution Principle
  4. I - Interface Segregation Principle
  5. D - Dependency Inversion Principle

1. Single Responsibility Principle


class User {
    public function saveToDatabase() {
        // Save logic
    }
}

Design Patterns

Implement patterns like Singleton, Factory, and Observer.

Code Documentation

Write PHPDoc comments for better code understanding.

Performance Optimization

Optimize PHP code and database queries.

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12. Interview Preparation

Common PHP Interview Questions

Prepare for frequently asked PHP interview questions.

Algorithm Challenges in PHP

Solve problems like reversing strings or finding duplicates.

Whiteboard Coding Tips

Practice coding on a whiteboard or paper.

System Design Concepts

Design scalable systems like e-commerce platforms.

Real-world Scenario Questions

Answer scenario-based questions about PHP applications.

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13. Projects and Practice

E-commerce System

Build a full-featured e-commerce platform.

REST API with Authentication

Create a secure REST API with JWT authentication.

CMS Implementation

Develop a content management system.

CLI Tool Development

Build command-line tools for automation.

Microservices Architecture

Design and implement microservices.

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14. Resources

Official PHP Documentation

Refer to the official PHP manual.

PHP: The Right Way

Follow best practices from “PHP: The Right Way.”

Read books like “Modern PHP” and “PHP Objects, Patterns, and Practice.”

Learning Platforms

Use platforms like Laracasts and PHP School.

Community Blogs

Follow blogs like PHP.net and Sitepoint.

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License

MIT