Repository pattern in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Repository pattern example?

Consider this PHP code using a simple repository pattern to fetch user data.

<?php
interface UserRepository {
    public function findUserById(int $id): ?array;
}

class InMemoryUserRepository implements UserRepository {
    private array $users = [
        1 => ['id' => 1, 'name' => 'Alice'],
        2 => ['id' => 2, 'name' => 'Bob']
    ];

    public function findUserById(int $id): ?array {
        return $this->users[$id] ?? null;
    }
}

$repo = new InMemoryUserRepository();
$user = $repo->findUserById(2);
echo $user['name'] ?? 'Not found';
?>

What will this code print?

PHP

<?php
interface UserRepository {
    public function findUserById(int $id): ?array;
}

class InMemoryUserRepository implements UserRepository {
    private array $users = [
        1 => ['id' => 1, 'name' => 'Alice'],
        2 => ['id' => 2, 'name' => 'Bob']
    ];

    public function findUserById(int $id): ?array {
        return $this->users[$id] ?? null;
    }
}

$repo = new InMemoryUserRepository();
$user = $repo->findUserById(2);
echo $user['name'] ?? 'Not found';
?>

A Not found

B Bob

C Alice

D Fatal error: Uncaught Error: Undefined array key 2

💡 Hint

Look at the user ID requested and the data stored in the repository.

The repository stores two users: Alice with ID 1 and Bob with ID 2. The code fetches user with ID 2, which is Bob, so it prints 'Bob'.

🧠 Conceptual

intermediate

Which statement best describes the Repository pattern?

Choose the best description of the Repository pattern in software design.

A It separates data access logic from business logic by providing a collection-like interface to access domain objects.

B It is a pattern to directly connect the UI with the database for faster queries.

C It is a design pattern that forces all data to be stored in memory for quick access.

D It is a pattern that replaces the need for any database or external storage.

💡 Hint

Think about how the Repository pattern helps organize code related to data.

The Repository pattern abstracts data access, providing a simple interface to retrieve and store domain objects, keeping business logic separate from data storage details.

🔧 Debug

advanced

What error does this Repository pattern code produce?

Examine this PHP code snippet using a repository pattern:

<?php
class UserRepository {
    private array $users = [];

    public function findUserById(int $id): array {
        return $this->users[$id];
    }
}

$repo = new UserRepository();
$user = $repo->findUserById(1);
echo $user['name'];
?>

What error will this code cause when run?

PHP

<?php
class UserRepository {
    private array $users = [];

    public function findUserById(int $id): array {
        return $this->users[$id];
    }
}

$repo = new UserRepository();
$user = $repo->findUserById(1);
echo $user['name'];
?>

A No error, prints empty string

B Notice: Undefined variable: users

C Parse error: syntax error, unexpected 'echo' (T_ECHO)

D Fatal error: Uncaught Error: Undefined array key 1

💡 Hint

Check what data is stored in the repository before accessing it.

The users array is empty, so accessing $this->users[1] causes an undefined array key error.

📝 Syntax

advanced

Which option correctly implements a Repository interface in PHP?

Given this interface:

<?php
interface ProductRepository {
    public function findProductById(int $id): ?array;
}
?>

Which class correctly implements this interface?

A

class MyRepo implements ProductRepository {
    public function findProductById(int $id): array {
        return [];
    }
}

B

class MyRepo implements ProductRepository {
    public function findProductById($id) {
        return [];
    }
}

C

class MyRepo implements ProductRepository {
    public function findProductById(int $id): ?array {
        return null;
    }
}

D

class MyRepo implements ProductRepository {
    public function findProductById(int $id) {
        return null;
    }
}

💡 Hint

Check method signature matches exactly including return type and parameter types.

Option C matches the interface method signature exactly, including parameter type and nullable array return type.

🚀 Application

expert

How many items are in the repository after these operations?

Consider this PHP repository class and usage:

<?php
class ItemRepository {
    private array $items = [];

    public function addItem(array $item): void {
        $this->items[$item['id']] = $item;
    }

    public function removeItem(int $id): void {
        unset($this->items[$id]);
    }

    public function getAllItems(): array {
        return array_values($this->items);
    }
}

$repo = new ItemRepository();
$repo->addItem(['id' => 1, 'name' => 'Pen']);
$repo->addItem(['id' => 2, 'name' => 'Pencil']);
$repo->addItem(['id' => 3, 'name' => 'Eraser']);
$repo->removeItem(2);
$repo->addItem(['id' => 2, 'name' => 'Marker']);
$items = $repo->getAllItems();
echo count($items);
?>

What number will be printed?

PHP

<?php
class ItemRepository {
    private array $items = [];

    public function addItem(array $item): void {
        $this->items[$item['id']] = $item;
    }

    public function removeItem(int $id): void {
        unset($this->items[$id]);
    }

    public function getAllItems(): array {
        return array_values($this->items);
    }
}

$repo = new ItemRepository();
$repo->addItem(['id' => 1, 'name' => 'Pen']);
$repo->addItem(['id' => 2, 'name' => 'Pencil']);
$repo->addItem(['id' => 3, 'name' => 'Eraser']);
$repo->removeItem(2);
$repo->addItem(['id' => 2, 'name' => 'Marker']);
$items = $repo->getAllItems();
echo count($items);
?>

A 3

B 2

C 1

D 4

💡 Hint

Count how many unique items remain after adding and removing by ID.

Initially 3 items are added. Item with ID 2 is removed, then a new item with ID 2 is added again. So total items are 3.