如何將IRepository <Invoice>和IRepository <Estimate>作爲IRepository <SalesTransaction>進行抽象？

Question

我有以下的階層結構

public abstract class SalesTransaction 
{ 

} 

public class Invoice : SalesTransaction 
{ 

} 

public class Estimate : SalesTransaction 
{ 

} 

public interface IRepostory<T> 
{ 
    T First(Expression<Func<T, bool>> predicate); 
    void Add(T item); 
    T Single(Expression<Func<T, bool>> predicate, bool disableTracking = false); 
} 

我可以以某種方式通過它鑄造IRepository<SalesTransaction>抽象IRepository<Invoice>和IRepository<Estimate>？

IRepository<Invoice> invoiceRepository = /* Create instance */; 
IRepository<SalesTransaction> salesTransaction = invoiceRepository; 

上面的代碼不能編譯。是否有解決方法讓它能夠編譯和工作？

Answer 1

您可以創建一個SalesTransaction存儲庫作爲更具體類型的存儲庫的包裝。 （此處以發票）

public class InvoiceAsSalesTransactionRepository : IRepostory<SalesTransaction> 
{ 
    private readonly IRepostory<Invoice> _invoiceRepository = new InvoiceRepository(); 

    public void Add(SalesTransaction item) 
    { 
     if (item is Invoice invoice) { 
      _invoiceRepository.Add(invoice); 
     } else { 
      throw new ArgumentException("Item must be Invoice"); 
     } 
    } 

    public SalesTransaction First(Expression<Func<SalesTransaction, bool>> predicate) 
    { 
     return _invoiceRepository.First(ToInvoicePredicate(predicate)); 
    } 

    public SalesTransaction Single(Expression<Func<SalesTransaction, bool>> predicate, 
            bool disableTracking = false) 
    { 
     return _invoiceRepository.Single(ToInvoicePredicate(predicate), disableTracking); 
    } 

    private static Expression<Func<Invoice, bool>> ToInvoicePredicate(
     Expression<Func<SalesTransaction, bool>> predicate) 
    { 
     var param = Expression.Parameter(typeof(Invoice), predicate.Parameters[0].Name); 
     return Expression.Lambda<Func<Invoice, bool>>(predicate.Body, param); 
    } 
} 

正如你所看到的，你需要一些反射魔法謂詞類型轉換。因此，你不能簡單地施放你的倉庫。請注意，我們不需要在此處施放任何內容，因爲有效的SalesTansaction謂詞始終是有效的Invoice謂詞，因爲SalesTansaction僅包含Invoices中也可用的屬性。