Repository pattern in PHP - Mini Project: Build & Apply

Repository Pattern in PHP

📖 Scenario: You are building a simple PHP application to manage a list of books. To keep your code clean and organized, you want to use the Repository pattern. This pattern helps separate the data storage logic from the rest of your application.

🎯 Goal: Create a basic Repository pattern implementation in PHP to store and retrieve books. You will create a data array, a repository class, and use it to get all books.

📋 What You'll Learn

Create an array of books with exact titles and authors

Create a BookRepository class with a method to get all books

Use the repository to retrieve and print the list of books

💡 Why This Matters

🌍 Real World

The Repository pattern helps keep your PHP code organized by separating data access from business logic. This makes your code easier to maintain and test.

💼 Career

Many PHP frameworks and professional projects use the Repository pattern to manage data. Knowing this pattern is useful for backend development jobs.

1

Create the books data array

Create a PHP array called $books with these exact entries: ['title' => '1984', 'author' => 'George Orwell'], ['title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee'], and ['title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald'].

PHP

<?php
// Create the books array with exact entries
// Your code here

Hint

Use a PHP array with three associative arrays inside, each with keys title and author.

2

Create the BookRepository class

Create a PHP class called BookRepository with a private property $books to hold the books array. Add a constructor that accepts a parameter $books and assigns it to the property $this->books.

PHP

 '1984', 'author' => 'George Orwell'],
    ['title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee'],
    ['title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald']
];

// Create the BookRepository class with private $books and constructor
// Your code here

Hint

Define a class with a private property and a constructor that sets this property from the parameter.

3

Add a method to get all books

Inside the BookRepository class, add a public method called getAll() that returns the $books property.

PHP

 '1984', 'author' => 'George Orwell'],
    ['title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee'],
    ['title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald']
];

class BookRepository {
    private array $books;

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

    // Add getAll() method to return $books
    // Your code here
}

Hint

Write a public method that returns the private books property.

4

Use the repository and print all books

Create an instance of BookRepository called $repository using the $books array. Then, use $repository->getAll() to get all books and print each book's title and author in the format: Title: [title], Author: [author] on separate lines.

PHP

 '1984', 'author' => 'George Orwell'],
    ['title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee'],
    ['title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald']
];

class BookRepository {
    private array $books;

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

    public function getAll(): array {
        return $this->books;
    }
}

// Create $repository and print all books
// Your code here

Hint

Create the repository object and loop through the books returned by getAll(). Use echo to print each book's details.

Practice

1. What is the main purpose of the Repository pattern in PHP?

easy

A. To separate data access logic from business logic

B. To directly connect the database with the user interface

C. To write all code inside a single class

D. To avoid using interfaces in the code

Solution

1. Step 1: Understand the role of Repository pattern

   The Repository pattern is designed to separate how data is accessed from how the business logic works.

2. Step 2: Identify the correct purpose

   Separating data access from business logic makes code cleaner and easier to maintain.

3. Final Answer:

   To separate data access logic from business logic -> Option A

4. Quick Check:

   Repository pattern = separation of concerns [OK]

Hint: Remember: Repository separates data logic from business logic [OK]

Common Mistakes:

• Thinking Repository connects UI directly to database
• Believing all code should be in one class
• Ignoring the use of interfaces

2. Which of the following is the correct way to declare a Repository interface in PHP?

easy

A. UserRepository interface { public function findUser(int $id); }

B. class UserRepository { public function findUser(int $id); }

C. interface UserRepository { function findUser; }

D. interface UserRepository { public function findUser(int $id); }

Solution

1. Step 1: Recall PHP interface syntax

   Interfaces use the keyword interface followed by method declarations with parentheses and types.

2. Step 2: Check each option

   interface UserRepository { public function findUser(int $id); } correctly declares an interface with a method having a typed parameter. class UserRepository { public function findUser(int $id); } uses class instead of interface. interface UserRepository { function findUser; } misses parentheses. UserRepository interface { public function findUser(int $id); } has wrong syntax order.

3. Final Answer:

   interface UserRepository { public function findUser(int $id); } -> Option D

4. Quick Check:

   Interface syntax = interface UserRepository { public function findUser(int $id); } [OK]

Hint: Interfaces use 'interface' keyword and method signatures with parentheses [OK]

Common Mistakes:

• Using 'class' instead of 'interface'
• Omitting parentheses in method declaration
• Wrong keyword order in interface declaration

3. Given the following PHP code, what will be the output?

interface UserRepository {
    public function findUser(int $id);
}

class UserRepo implements UserRepository {
    public function findUser(int $id) {
        return "User_" . $id;
    }
}

$repo = new UserRepo();
echo $repo->findUser(5);

medium

A. 5

B. User_5

C. UserRepo

D. Error: Interface method not implemented

Solution

1. Step 1: Understand interface and class implementation

   The class UserRepo implements UserRepository and defines the method findUser that returns "User_" concatenated with the id.

2. Step 2: Trace the method call

   Calling $repo->findUser(5) returns "User_5" which is then printed.

3. Final Answer:

   User_5 -> Option B

4. Quick Check:

   Method returns 'User_' + id = User_5 [OK]

Hint: Look for string concatenation in method return [OK]

Common Mistakes:

• Expecting just the number 5 as output
• Confusing class name with output
• Thinking interface causes error if implemented correctly

4. Identify the error in this PHP Repository implementation:

interface ProductRepository {
    public function getProduct(int $id);
}

class ProductRepo implements ProductRepository {
    public function getProduct() {
        return "Product";
    }
}

medium

A. Class name should be ProductRepository, not ProductRepo

B. Interface keyword is misspelled

C. Method getProduct() missing parameter in class implementation

D. Return type is missing in interface method

Solution

1. Step 1: Compare interface and class method signatures

   The interface method getProduct requires an int $id parameter, but the class method has no parameters.

2. Step 2: Understand PHP interface implementation rules

   When implementing an interface, method signatures must match exactly, including parameters.

3. Final Answer:

   Method getProduct() missing parameter in class implementation -> Option C

4. Quick Check:

   Method signatures must match [OK]

Hint: Check method parameters match interface exactly [OK]

Common Mistakes:

• Ignoring parameter mismatch
• Thinking class name must match interface name
• Assuming return type is mandatory in interface

5. You want to create a flexible Repository pattern for managing users and products. Which design approach best supports adding new data types without changing existing code?

hard

A. Create separate interfaces like UserRepository and ProductRepository, then implement them in separate classes

B. Write one big class handling all data types with many methods

C. Use global functions to access data directly

D. Store all data in arrays inside a single class without interfaces

Solution

1. Step 1: Understand flexibility in Repository pattern

   Using separate interfaces and classes for each data type allows adding new repositories without changing existing ones.

2. Step 2: Evaluate options for maintainability

   Create separate interfaces like UserRepository and ProductRepository, then implement them in separate classes supports open/closed principle: open for extension, closed for modification. Other options mix concerns or lack structure.

3. Final Answer:

   Create separate interfaces like UserRepository and ProductRepository, then implement them in separate classes -> Option A

4. Quick Check:

   Separate interfaces = flexible extension [OK]

Hint: Use separate interfaces and classes for each data type [OK]

Common Mistakes:

• Putting all logic in one big class
• Using global functions instead of classes
• Avoiding interfaces reduces flexibility