Repository pattern in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Repository pattern?

The Repository pattern is a way to separate data access logic from business logic. It acts like a middleman between your app and the database, making code easier to manage and test.

beginner

Why use the Repository pattern in PHP?

Using the Repository pattern helps keep your code clean by hiding database details. It also makes switching databases easier and improves testing by allowing you to mock data sources.

intermediate

What is the main role of a Repository interface?

A Repository interface defines the methods for data operations like add, find, update, and delete. It sets a contract that any repository class must follow.

intermediate

How does the Repository pattern improve testing?

It allows you to replace the real database with fake data sources during tests. This makes tests faster and more reliable because they don't depend on a real database.

beginner

Show a simple example of a Repository interface method in PHP.

Example: <pre>interface UserRepository {
    public function findUserById(int $id): ?User;
}</pre> This method finds a user by their ID or returns null if not found.

What does the Repository pattern mainly help with?

A Improving user interface design

B Encrypting data in the database

C Separating data access from business logic

D Managing server configurations

The Repository pattern separates data access logic from business logic to keep code organized.

Which of these is a benefit of using the Repository pattern?

A Makes switching databases easier

B Slows down application performance

C Requires more database queries

D Removes the need for testing

The Repository pattern hides database details, making it easier to switch databases.

What does a Repository interface define?

A Server connection settings

B User interface layout

C CSS styles for the app

D Methods for data operations like add, find, update, delete

A Repository interface defines the methods for data operations.

How does the Repository pattern help with testing?

A Allows replacing real database with fake data sources

B Automatically writes test cases

C Runs tests faster by skipping logic

D Prevents any bugs in code

It allows tests to use fake data sources instead of a real database.

Which PHP code snippet shows a Repository interface method?

A echo 'Hello World';

B public function findUserById(int $id): ?User;

C $db->connect();

D class User {}

This method signature is typical for a Repository interface.

Explain the Repository pattern and why it is useful in PHP applications.

Think about how your app talks to the database and how the Repository acts as a middleman.

Describe how you would create a Repository interface and implement it for a User entity in PHP.

Start with the contract (interface), then write the class that follows it.

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