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What is repository design pattern c# | design pattern in c# | C# interview question for experienced person
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np

Sun , Oct 05 2025

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What is the Repository pattern in C# ?

Lets understand -
The Repository pattern in C# is a design pattern that abstracts the data access layer from the business logic layer of an application. Its primary purpose is to decouple how data is retrieved and persisted from the specific data source technology (e.g., a relational database, a NoSQL database, or a web service).
in Simple words this pattern support the architecture where all data related stuff like Model classes and DB properties should be taken care in a separate class library with interface declaration, so that dependent class can implement this interface and define the expected functionality by these interface in this way it support onion architecture and decoupling concept and dependency inversion principle. 
Core Concepts:
  • Abstraction of Data Access: 
    It encapsulates the logic for interacting with a data source within a dedicated class, preventing the business logic from directly dealing with database-specific concerns like connections, commands, or ORM details.
  • Collection-like Interface: 
    A repository typically provides methods that mimic the operations of a collection, such as Add, GetById, Update, and Delete, allowing the business logic to interact with domain objects as if they were in-memory collections.
  • Separation of Concerns: 
    This pattern promotes a clear separation between the data access layer and the application's business logic, leading to cleaner, more maintainable, and testable code.
  • Testability: 
    By defining an interface for the repository, it becomes easy to mock the data access layer during unit testing, isolating the business logic and ensuring its independent functionality.
  • Flexibility: 
    It allows for changes in the underlying data storage technology without requiring modifications to the business logic, as long as the repository implementation adheres to the defined interface.



     
Implementation in C#:
A common implementation involves:
  • Defining an Interface: An interface (e.g., IProductRepository) is created to define the contract for data access operations, specifying methods like GetProductById(int id), AddProduct(Product product), etc.  

  • public interface IProductRepository
        {
            Product GetProductById(int id);
            IEnumerable<Product> GetAllProducts();
            void AddProduct(Product product);
            void UpdateProduct(Product product);
            void DeleteProduct(int id);
        }
  •  
  • Creating a Concrete Class: A concrete class (e.g., ProductRepository) implements the interface and contains the actual logic for interacting with the data source, often using an ORM like Entity Framework Core or Dapper. 

  •     public class ProductRepository : IProductRepository
  •     {
  •         private readonly ApplicationDbContext _context; // Example for EF Core

  •         public ProductRepository(ApplicationDbContext context)
  •         {
  •             _context = context;
  •         }

  •         public Product GetProductById(int id)
  •         {
  •             return _context.Products.Find(id);
  •         }

  •         // ... other methods implementing the interface
  •     }

  •  
  • Dependency Injection: In modern C# applications (especially ASP.NET Core), dependency injection is used to inject the IProductRepository into controllers or services, allowing them to interact with the data layer without knowing the concrete implementation.
    • Benefits:
    • Improved maintainability and testability.
    • Decoupling of data access and business logic.
    • Easier to swap out data storage technologies.
    • Reduced code duplication for common data operations (especially with generic repositories).

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np

np

I am an engineer with over 10 years of experience, passionate about using my knowledge and skills to make a difference in the world. By writing on LifeDB, I aim to share my thoughts, ideas, and insights to inspire positive change and contribute to society. I believe that even small ideas can create big impacts, and I am committed to giving back to the community in every way I can.

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