I would separate the BLL from DAL as a best practice. I interact between BLL and DAL via interface. Example:

public interface IProductRepository {     void Add(Product myProduct);     Product Get(string name);     Product GetById(int id); } 

where business object Product is:

public class Product {      public int Id { get; set; }      public string Name { get; set; }      public decimal Price { get; set; } } 

The BLL class is:

public class ProductManager {      private readonly IProductRepository productRepository;       public ProductManager(IProductRepository productRepository)      {           this.productRepository = productRepository ?? throw new Exception("message");      }      public void AddProduct(Product myProduct)     {         try         {                               // Here code validation ecc....              // Add product to database             productRepository.Add(myProduct);         }         catch(Exception e)         {             // Handle exception           }     }       public Product GetProduct(string name)     {         try         {             // Here code to validation ecc....              // Get product from database             var product = _productRepository.Get(name);              return product;         }         catch(Exception e)         {             // Handle exception           }     }      // ecc ecc } 

where DAL (i would use Entity Framework) is:

public ProductRepository : IProductRepository {     public void Add(Product myProduct)     {         using(var dbContext = MyDbContext())         {             var dbProduct = new PRODUCTS             {                 NAME = myProduct.Name,                 PRICE = myProduct.Price             }              dbContext.PRODUCT.Add(dbProduct);              dbContext.SaveChanges();         }     }      // ecc ecc } 

Now I have some questions: – Is this the correct implementation? – If I want insert a product but I want to check if a product with the same name is on db, do I first call the Get method in BLL and then call Add method (the db context is open and closed each time, is an overload?) or I can insert logic in DAL like:

var dbProduct = dbContext.PRODUCTS.FirstOrDefault(p => p.NAME == name);  if(dbProduct == null) .... // insert else throw exception  

In the latter case, however, if a change the dal the bll logig would no work anymore. -Is it right to use EntityFramework in this way, or do I lose all the benefits of linq? Sorry, but i’m very confused.

Thank you.