The RepositoryPattern is a design pattern that acts as a
mediator between the business logic and the data access layer. It provides a consistent way to
access, manage, and query data, while hiding the details of data storage.
Definition
A repository is a collection-like interface for accessing domain objects, centralizing data logic or querying logic to keep the application clean and maintainable.
Purpose of Repository Pattern
Encapsulate data access logic
Promote separation of concerns
Improve testability (mocking the repository)
Enable switching between different data sources (e.g., from SQL to NoSQL)
Reduce code duplication for common data operations
Structure of Repository Pattern
Controller → Service/Business Layer → Repository → Data Source (DB)
Typical Repository Interface
public interface IRepository<T>
{
T GetById(int id);
IEnumerable<T> GetAll();
void Add(T entity);
void Delete(T entity);
void Update(T entity);
}
Concrete Implementation Example
public class UserRepository : IRepository<User>
{
private readonly DbContext _context;
public UserRepository(DbContext context)
{
_context = context;
}
public User GetById(int id) => _context.Users.Find(id);
public IEnumerable<User> GetAll() => _context.Users.ToList();
public void Add(User user) => _context.Users.Add(user);
public void Delete(User user) => _context.Users.Remove(user);
public void Update(User user) => _context.Users.Update(user);
}
When to Use the Repository Pattern
Situation
Use Repository Pattern?
Complex data logic in controllers
✅ Yes
Need to unit test business logic
✅ Yes
Want to abstract away EF Core
✅ Yes
Simple CRUD-only apps
❌ May be overkill
Benefits
Decouples business logic from data logic
Makes code more readable and maintainable
Supports unit testing with mock repositories
Promotes DRY (Don't Repeat Yourself) principle
Drawbacks
Can introduce unnecessary abstraction in simple applications
If overused, may lead to code duplication or complexity
With EF Core, the DbContext already acts like a repository
Summary
Aspect
Repository Pattern
Main Goal
Abstract data access logic
Improves
Testability, maintainability
Best For
Medium to large apps with business logic
Not Ideal For
Simple apps with only CRUD
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What is the Repository Pattern in C#?
Definition
Purpose of Repository Pattern
Structure of Repository Pattern
Typical Repository Interface
Concrete Implementation Example
When to Use the Repository Pattern
Benefits
Drawbacks
Summary