Design Patterns

The Repository Pattern: Abstracting Data Access Logic

nemostorm•January 11, 2026•11 min read

The Repository Pattern: Abstracting Data Access Logic

What is the Repository Pattern?

The Repository Pattern is a design pattern that mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects. It acts as an abstraction layer between your business logic and data access code, making your application more maintainable, testable, and flexible.

The Problem It Solves

Imagine you're building an e-commerce application. Without the Repository Pattern, your business logic might be tightly coupled to your database:

csharp

public class OrderService
{
    private readonly SqlConnection _connection;

    public OrderService(string connectionString)
    {
        _connection = new SqlConnection(connectionString);
    }

    public Order GetOrder(int orderId)
    {
        var command = new SqlCommand("SELECT * FROM Orders WHERE Id = @Id", _connection);
        command.Parameters.AddWithValue("@Id", orderId);
        
        _connection.Open();
        var reader = command.ExecuteReader();
        // Manual mapping logic...
        _connection.Close();
        
        return order;
    }
}

The Solution: Repository Pattern

The interactive code editor above demonstrates the Repository Pattern implementation:

1. Repository Interface: Defines the contract for data access operations 2. Concrete Repository: Implements the interface with actual data access logic 3. Unit of Work: Manages transactions and coordinates multiple repositories 4. Dependency Injection: Provides repositories to business logic classes

Benefits of the Repository Pattern

Abstraction: Business logic doesn't depend on data access details
Testability: Easy to mock repositories for unit testing
Flexibility: Can switch data sources without changing business logic
Maintainability: Centralized data access logic
Consistency: Uniform interface for all data operations

When to Use the Repository Pattern

Use when:

Working with complex business logic
Need to support multiple data sources
Writing comprehensive unit tests
Building large-scale applications
Data access logic is complex

Don't use when:

Simple CRUD operations
Already using a full-featured ORM
Performance is critical (adds abstraction overhead)
Data access is trivial

Conclusion

The Repository Pattern provides a clean abstraction between your business logic and data access layer. It improves testability, maintainability, and flexibility by isolating data access code.

However, modern ORMs like Entity Framework Core already provide many repository-like features through DbContext. Before implementing the Repository Pattern, consider whether the added abstraction provides real value for your specific use case, or if it's creating unnecessary complexity.

When used appropriately, the Repository Pattern is a powerful tool for building maintainable, testable applications with clean architecture.