Repository pattern in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Repository pattern in mobile app development?

The Repository pattern is a way to organize code that separates data access logic from the rest of the app. It acts like a middleman between the app and data sources, making it easier to manage and test data operations.

beginner

Why use the Repository pattern in an iOS app?

Using the Repository pattern helps keep your app clean and organized. It hides where data comes from (like a database or web service), so the app code doesn’t need to change if the data source changes.

intermediate

In Swift, what does a Repository typically provide?

A Repository usually provides methods to fetch, save, update, or delete data. These methods return data in a simple way, so the rest of the app can use it without worrying about details.

intermediate

How does the Repository pattern improve testing?

Because the Repository hides data sources, you can replace it with a fake or mock version during testing. This lets you test app logic without needing real data or network calls.

beginner

Give a simple example of a Repository interface in Swift.

protocol UserRepository { func fetchUsers() async throws -> [User] func saveUser(_ user: User) async throws }

What is the main role of a Repository in an app?

A To manage data access and hide data source details

B To handle user interface layout

C To manage app navigation

D To store app settings

The Repository manages data access and hides where data comes from, keeping the app code clean.

Which benefit does the Repository pattern provide for testing?

A Simplifies UI design

B Improves app speed

C Allows replacing data source with mocks

D Manages app permissions

Repositories can be swapped with fake versions during tests, so real data or network calls are not needed.

In Swift, how do you define a Repository interface?

A Using an enum with cases

B Using a protocol with data methods

C Using a struct with colors

D Using a class with UI elements

A protocol defines the methods a Repository must implement, like fetching or saving data.

What kind of methods does a Repository usually have?

A Fetch, save, update, delete data

B Draw buttons and labels

C Handle user gestures

D Manage app lifecycle events

Repositories provide methods to work with data, such as fetching or saving.

Which of these is NOT a reason to use the Repository pattern?

A To separate data logic from UI

B To simplify testing with mocks

C To make data source changes easier

D To improve app navigation speed

Repository pattern does not directly affect navigation speed; it focuses on data management.

Explain the Repository pattern and why it is useful in iOS app development.

Think about how your app talks to data and how Repository helps keep that simple.

Describe how you would create a simple UserRepository in Swift and what methods it might have.

Focus on the interface that hides data details from the rest of the app.

Practice

1.

What is the main purpose of the Repository pattern in iOS Swift development?

easy

A. To separate data access logic from the rest of the app

B. To handle UI animations smoothly

C. To manage app navigation between screens

D. To store user interface layout information

Solution

1. Step 1: Understand the role of Repository pattern

   The Repository pattern is designed to isolate data access logic from business logic in an app.

2. Step 2: Identify the correct purpose

   Separating data access makes the app easier to maintain and test, which matches To separate data access logic from the rest of the app.

3. Final Answer:

   To separate data access logic from the rest of the app -> Option A

4. Quick Check:

   Repository pattern = separate data access [OK]

Hint: Repository = data access separation [OK]

Common Mistakes:

• Confusing Repository with UI or navigation roles
• Thinking Repository manages animations
• Assuming Repository stores UI layout

2.

Which of the following is the correct way to declare a repository protocol in Swift?

?

easy

A. struct UserRepository { func fetchUsers() -> [User] }

B. class UserRepository { func fetchUsers() -> [User] }

C. enum UserRepository { func fetchUsers() -> [User] }

D. protocol UserRepository { func fetchUsers() -> [User] }

Solution

1. Step 1: Identify correct Swift syntax for protocols

   Protocols in Swift are declared with the keyword protocol followed by method signatures without bodies.

2. Step 2: Match the correct declaration

   protocol UserRepository { func fetchUsers() -> [User] } correctly declares a protocol with a method signature. Other options use class, struct, or enum which are not protocols.

3. Final Answer:

   protocol UserRepository { func fetchUsers() -> [User] } -> Option D

4. Quick Check:

   Protocol declaration uses protocol keyword [OK]

Hint: Protocols start with 'protocol' keyword [OK]

Common Mistakes:

• Using class or struct instead of protocol for interface
• Adding method bodies inside protocol
• Using enum incorrectly for repository

3.

Given the following code snippet, what will be printed?

protocol UserRepository {
  func fetchUsers() -> [String]
}

class MockUserRepository: UserRepository {
  func fetchUsers() -> [String] {
    return ["Alice", "Bob"]
  }
}

let repo: UserRepository = MockUserRepository()
print(repo.fetchUsers())

medium

A. []

B. ["Alice", "Bob"]

C. nil

D. Compilation error

Solution

1. Step 1: Understand protocol conformance and method implementation

   The class MockUserRepository conforms to UserRepository and implements fetchUsers() returning ["Alice", "Bob"].

2. Step 2: Analyze the print statement

   The variable repo is typed as UserRepository but holds an instance of MockUserRepository. Calling fetchUsers() returns ["Alice", "Bob"], which is printed.

3. Final Answer:

   ["Alice", "Bob"] -> Option B

4. Quick Check:

   Protocol method returns mock data [OK]

Hint: Protocol variable calls concrete implementation [OK]

Common Mistakes:

• Expecting empty array instead of returned data
• Thinking protocol variable can't call methods
• Assuming compilation error due to protocol

4.

Identify the error in this repository implementation:

protocol UserRepository {
  func fetchUsers() -> [String]
}

class UserRepo: UserRepository {
  func fetchUsers() {
    return ["Alice", "Bob"]
  }
}

medium

A. Protocol method has wrong name

B. Method does not return a value

C. Missing return type in method signature

D. Class does not conform to protocol

Solution

1. Step 1: Compare protocol and class method signatures

   The protocol method fetchUsers() returns [String]. The class method lacks the return type in its signature.

2. Step 2: Identify the mismatch causing error

   Because the class method signature does not match the protocol, it causes a compilation error. The method must declare the return type.

3. Final Answer:

   Missing return type in method signature -> Option C

4. Quick Check:

   Method signatures must match protocol [OK]

Hint: Method signature must match protocol exactly [OK]

Common Mistakes:

• Forgetting to add return type in implementation
• Assuming method name mismatch
• Thinking protocol conformance is automatic

5.

You want to switch your data source from a local database to a remote API without changing your app's business logic. How does the Repository pattern help you achieve this?

hard

A. By defining a repository interface and implementing separate classes for each data source

B. By embedding API calls directly in the UI code

C. By storing all data in global variables accessible everywhere

D. By using a single class that mixes local and remote data fetching

Solution

1. Step 1: Understand the role of repository interface

   The Repository pattern uses an interface (protocol) to abstract data access methods.

2. Step 2: Implement separate classes for each data source

   You create one class for local database access and another for remote API, both conforming to the same interface. This allows switching without changing business logic.

3. Final Answer:

   By defining a repository interface and implementing separate classes for each data source -> Option A

4. Quick Check:

   Interface + multiple implementations = easy data source switch [OK]

Hint: Use interface + multiple classes for data sources [OK]

Common Mistakes:

• Mixing data fetching code in UI layer
• Using global variables for data access
• Combining local and remote logic in one class