Repository Pattern

The Repository Pattern in a Design Driven Development or software design pattern used to abstract the data access layer of an application. It acts as a middleman between your business logic and the underlying data source (such as a database or an external service). It provides an abstraction over the underlying data.

Simple Definition

A repository is like a virtual collection of data objects that you can query, add to, update, or remove — without knowing how or where that data is actually stored.

Why Use the Repository Pattern?

The Repository Pattern provides key benefits in enterprise-scale software systems:

Benefit	Explanation
Separation of Concerns	Keeps business logic separate from data access logic.
Code Reusability	Centralises common data access logic in one place.
Testability	Makes it easier to mock or stub the data layer in unit tests.
Flexibility	Lets you switch databases or data sources with minimal code changes.

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How It Works – For Engineers

A repository typically exposes methods like:

public interface ICustomerRepository
{
    Task<Customer> GetByIdAsync(Guid id);
    Task<IEnumerable<Customer>> GetAllAsync();
    Task AddAsync(Customer customer);
    Task UpdateAsync(Customer customer);
    Task DeleteAsync(Guid id);
}

You can then implement the interface using, for example, Entity Framework or Dapper:

public class CustomerRepository : ICustomerRepository
{
    private readonly AppDbContext _context;

    public CustomerRepository(AppDbContext context)
    {
        _context = context;
    }

    public async Task<Customer> GetByIdAsync(Guid id)
    {
        return await _context.Customers.FindAsync(id);
    }

    // Other methods...
}

Where It Fits in a C# Microservice

In a typical layered architecture, the repository is part of the data access layer:

[ Controller / API ]
        ↓
[ Service Layer ]
        ↓
[ Repository Pattern ]
        ↓
[ Database / External Source ]

• The controller handles HTTP requests.
• The service layer contains business logic.
• The repository performs data access operations.
• The database stores the actual data.

Summary for Project Managers

• The Repository Pattern is a software structure that cleanly separates how data is stored from how it’s used.
• It allows engineers to write cleaner, more maintainable code by isolating business rules from low-level data access details.
• It also helps with testing and long-term support, as changes in the data layer (like switching from SQL to NoSQL) require fewer changes to the rest of the system.

When Should You Use It?

Use Case	Recommendation
Complex business logic with many rules	✅ Strongly recommended
Microservice with a relational database	✅ Common pattern
Simple CRUD microservice	⚠️ May be overkill if kept too abstract