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mohamed Tayel
mohamed Tayel

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Specification Pattern P2

🚀 Step 2: Implementing a Generic Repository (Introducing Category Repository)

💡 Goal:

In this article, we will refactor our Product Repository by implementing a Generic Repository Pattern. Additionally, we will introduce the Category Repository, demonstrating how the Generic Repository improves code reusability and maintainability.

📂 Updated Project Structure (With Generic Repository) 

📂 ProductApp ├── 📂 Core # Domain Layer │ ├── 📂 Entities │ │ ├── BaseEntity.cs │ │ ├── Product.cs │ │ ├── Category.cs │ ├── 📂 Interfaces │ │ ├── IRepository.cs # Generic Repository Interface │ │ ├── IProductRepository.cs │ │ ├── ICategoryRepository.cs │ ├── 📂 Infrastructure # Data Access Layer │ ├── 📂 Data │ │ ├── Repository.cs # Generic Repository Implementation │ │ ├── ProductRepository.cs │ │ ├── CategoryRepository.cs │ │ ├── StoreContext.cs │ ├── 📂 API # Presentation Layer │ ├── 📂 Controllers │ │ ├── ProductsController.cs │ │ ├── CategoriesController.cs │ ├── 📂 DTOs │ │ ├── ProductDto.cs │ │ ├── CategoryDto.cs
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1️⃣ Define the Base Entity

📂 Core/Entities/BaseEntity.cs

namespace Core.Entities { public abstract class BaseEntity { public int Id { get; set; } } }
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2️⃣ Define the Generic Repository Interface

📂 Core/Interfaces/IRepository.cs

using System.Collections.Generic; using System.Threading.Tasks; namespace Core.Interfaces { public interface IRepository<T> where T : BaseEntity { Task<T?> GetByIdAsync(int id); Task<List<T>> ListAllAsync(); void Add(T entity); void Update(T entity); void Remove(T entity); Task<bool> SaveAllAsync(); } }
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3️⃣ Implement the Generic Repository

📂 Infrastructure/Data/Repository.cs

using System.Collections.Generic; using System.Threading.Tasks; using Core.Entities; using Core.Interfaces; using Microsoft.EntityFrameworkCore; namespace Infrastructure.Data { public class Repository<T> : IRepository<T> where T : BaseEntity { private readonly StoreContext _context; private readonly DbSet<T> _dbSet; public Repository(StoreContext context) { _context = context; _dbSet = _context.Set<T>(); } public async Task<T?> GetByIdAsync(int id) { return await _dbSet.FindAsync(id); } public async Task<List<T>> ListAllAsync() { return await _dbSet.ToListAsync(); } public void Add(T entity) { _dbSet.Add(entity); } public void Update(T entity) { _dbSet.Update(entity); } public void Remove(T entity) { _dbSet.Remove(entity); } public async Task<bool> SaveAllAsync() { return await _context.SaveChangesAsync() > 0; } } }
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4️⃣ Define the **Category**** Entity**

📂 Core/Entities/Category.cs

namespace Core.Entities { public class Category : BaseEntity { public string Name { get; set; } = string.Empty; } }
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5️⃣ Implement the **ICategoryRepository**** Interface**

📂 Core/Interfaces/ICategoryRepository.cs

using Core.Entities; namespace Core.Interfaces { public interface ICategoryRepository : IRepository<Category> { } }
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6️⃣ Implement the **CategoryRepository**

📂 Infrastructure/Data/CategoryRepository.cs

using Core.Entities; using Core.Interfaces; namespace Infrastructure.Data { public class CategoryRepository : Repository<Category>, ICategoryRepository { public CategoryRepository(StoreContext context) : base(context) { } } }
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7️⃣ Register the Repositories in **Program.cs**

📂 API/Program.cs

using Infrastructure.Data; using Microsoft.EntityFrameworkCore; var builder = WebApplication.CreateBuilder(args); // Add services to the container. builder.Services.AddControllers(); builder.Services.AddEndpointsApiExplorer(); builder.Services.AddSwaggerGen(); // Register StoreContext with Dependency Injection builder.Services.AddDbContext<StoreContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"))); // Register Repositories builder.Services.AddScoped(typeof(IRepository<>), typeof(Repository<>)); builder.Services.AddScoped<IProductRepository, ProductRepository>(); builder.Services.AddScoped<ICategoryRepository, CategoryRepository>(); var app = builder.Build(); // Apply Migrations Automatically (Optional: Good for development) using var scope = app.Services.CreateScope(); var services = scope.ServiceProvider; var context = services.GetRequiredService<StoreContext>(); context.Database.Migrate(); app.UseSwagger(); app.UseSwaggerUI(); app.UseHttpsRedirection(); app.UseAuthorization(); app.MapControllers(); app.Run();
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8️⃣ Create and Apply Migrations

Run the following commands in the API project folder:

# Create a Migration dPM> dotnet ef migrations add AddCategoryEntity No project was found. Change the current working directory or use the --project option. # Apply the Migration to Update the Database dotnet ef database update
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🚀 Step 2 is Complete

✔ We refactored the Product Repository using a Generic Repository.\
✔ We introduced the Category Repository, demonstrating reusability.\
✔ The Generic Repository now enables easy expansion for future entities.\
✔ We added and applied migrations to update the database.

🔜 What’s Next?

In the next article, we will introduce the Specification Pattern to handle complex queries efficiently. This will allow filtering, sorting, and pagination without cluttering our repositories.

Stay tuned! 🚀

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