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mohamed Tayel
mohamed Tayel

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Specification Pattern P1

#specificationpattern #csharp #designpatterns

🚀 Step 1: Case Study Without Generic Repository & Specification Pattern

💡 Goal: Implement a simple Product API using a separate repository for products.

📂 Project Structure (Without Generic Repository & Specification Pattern) 

📂 ProductApp ├── 📂 Core # Domain Layer │ ├── 📂 Entities │ │ ├── Product.cs │ ├── 📂 Interfaces │ │ ├── IProductRepository.cs │ ├── 📂 Infrastructure # Data Access Layer │ ├── 📂 Data │ │ ├── ProductRepository.cs │ │ ├── StoreContext.cs │ ├── 📂 API # Presentation Layer │ ├── 📂 Controllers │ │ ├── ProductsController.cs │ ├── 📂 DTOs │ │ ├── ProductDto.cs
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1️⃣ Install Required NuGet Packages

Before proceeding, install the necessary NuGet packages for Entity Framework Core and SQL Server support:

dotnet add package Microsoft.EntityFrameworkCore.SqlServer dotnet add package Microsoft.EntityFrameworkCore.Design dotnet add package Microsoft.EntityFrameworkCore.Tools
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2️⃣ Create the Product Entity

📂 Core/Entities/Product.cs

namespace Core.Entities { public class Product { public int Id { get; set; } public string Name { get; set; } = string.Empty; public string Brand { get; set; } = string.Empty; public string Type { get; set; } = string.Empty; public decimal Price { get; set; } } }
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3️⃣ Create the ProductDto for API Response

📂 API/DTOs/ProductDto.cs

namespace API.DTOs { public class ProductDto { public int Id { get; set; } public string Name { get; set; } = string.Empty; public string Brand { get; set; } = string.Empty; public string Type { get; set; } = string.Empty; public decimal Price { get; set; } } }
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4️⃣ Create the IProductRepository Interface

📂 Core/Interfaces/IProductRepository.cs

using System.Collections.Generic; using System.Threading.Tasks; using Core.Entities; namespace Core.Interfaces { public interface IProductRepository { Task<Product?> GetByIdAsync(int id); Task<List<Product>> ListAllAsync(); void Add(Product product); void Update(Product product); void Remove(Product product); Task<bool> SaveAllAsync(); } }
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5️⃣ Implement the ProductRepository

📂 Infrastructure/Data/ProductRepository.cs

using System.Collections.Generic; using System.Threading.Tasks; using Core.Entities; using Core.Interfaces; using Microsoft.EntityFrameworkCore; namespace Infrastructure.Data { public class ProductRepository : IProductRepository { private readonly StoreContext _context; public ProductRepository(StoreContext context) { _context = context; } public async Task<Product?> GetByIdAsync(int id) { return await _context.Products.FindAsync(id); } public async Task<List<Product>> ListAllAsync() { return await _context.Products.ToListAsync(); } public void Add(Product product) { _context.Products.Add(product); } public void Update(Product product) { _context.Products.Update(product); } public void Remove(Product product) { _context.Products.Remove(product); } public async Task<bool> SaveAllAsync() { return await _context.SaveChangesAsync() > 0; } } }
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6️⃣ Create the StoreContext (DbContext)

📂 Infrastructure/Data/StoreContext.cs

using Core.Entities; using Microsoft.EntityFrameworkCore; namespace Infrastructure.Data { public class StoreContext : DbContext { public StoreContext(DbContextOptions<StoreContext> options) : base(options) { } public DbSet<Product> Products { get; set; } } }
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7️⃣ Create the API Controller: ProductsController

📂 API/Controllers/ProductsController.cs

using API.DTOs; using Core.Entities; using Core.Interfaces; using Microsoft.AspNetCore.Mvc; namespace API.Controllers { [ApiController] [Route("api/[controller]")] public class ProductsController : ControllerBase { private readonly IProductRepository _productRepository; public ProductsController(IProductRepository productRepository) { _productRepository = productRepository; } [HttpGet] public async Task<ActionResult<IEnumerable<ProductDto>>> GetProducts() { var products = await _productRepository.ListAllAsync(); return Ok(products.Select(p => new ProductDto { Id = p.Id, Name = p.Name, Brand = p.Brand, Type = p.Type, Price = p.Price })); } [HttpGet("{id}")] public async Task<ActionResult<ProductDto>> GetProduct(int id) { var product = await _productRepository.GetByIdAsync(id); if (product == null) return NotFound(); return Ok(new ProductDto { Id = product.Id, Name = product.Name, Brand = product.Brand, Type = product.Type, Price = product.Price }); } [HttpPost] public async Task<ActionResult<ProductDto>> CreateProduct(ProductDto productDto) { var product = new Product { Name = productDto.Name, Brand = productDto.Brand, Type = productDto.Type, Price = productDto.Price }; _productRepository.Add(product); await _productRepository.SaveAllAsync(); return CreatedAtAction(nameof(GetProduct), new { id = product.Id }, productDto); } [HttpPut("{id}")] public async Task<IActionResult> UpdateProduct(int id, ProductDto productDto) { var product = await _productRepository.GetByIdAsync(id); if (product == null) return NotFound(); product.Name = productDto.Name; product.Brand = productDto.Brand; product.Type = productDto.Type; product.Price = productDto.Price; _productRepository.Update(product); await _productRepository.SaveAllAsync(); return NoContent(); } [HttpDelete("{id}")] public async Task<IActionResult> DeleteProduct(int id) { var product = await _productRepository.GetByIdAsync(id); if (product == null) return NotFound(); _productRepository.Remove(product); await _productRepository.SaveAllAsync(); return NoContent(); } } }
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8️⃣ Register StoreContext 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 Repository builder.Services.AddScoped<IProductRepository, ProductRepository>(); var app = builder.Build(); app.UseSwagger(); app.UseSwaggerUI(); app.UseHttpsRedirection(); app.UseAuthorization(); app.MapControllers(); app.Run();
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🎯 Final Steps: Running the API

  1. Run the following commands to apply migrations: 
dotnet ef migrations add InitialCreate --project ../Infrastructure/Data.csproj --startup-project API/ProductAPI.csproj dotnet ef database update --project ../Infrastructure/Data.csproj --startup-project API/ProductAPI.csproj
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  1. Start the API: 
dotnet run
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  1. Open Swagger UI at https://localhost:5001/swagger to test the endpoints.

🚀 Step 1 is Complete

✔ We implemented a Product API using a traditional repository.

✔ The API can Create, Read, Update, and Delete (CRUD) products.

Next Steps: Implement the Generic Repository to improve code reusability. 🚀

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