使用 「Linq的方法」 與日期時間處理

Question

[ASP.NET 4.0/4.1 EF]

嗨，

我正嘗試使用 「Linq的方法」 的基礎上日期時間字段來過濾數據源，但我收到錯誤：「在這種情況下只支持原始類型（如Int32，String和Guid）」。

我知道Entity Framework在處理日期時有一些限制，但我需要的是處理這個問題的一些優雅的解決方案。

我的代碼是：

public IList<Order> GetOrders(int? orderId = null, string customerId = null, int? employeeId = null, DateTime? orderDateFrom = null, DateTime? orderDateUntil=null, DateTime? requiredDate = null, DateTime? shippedDate = null) 
    { 
     IQueryable<Order> result; 

     result = from order in ctx.Orders.Include("Order_Details") 
       select order; 

     // Apply filters to the base query 
     if (orderId != null) 
      result = result.Where(o => o.OrderID.Equals(orderId)); 

     if (!String.IsNullOrEmpty(customerId)) 
      result = result.Where(o => o.CustomerID.ToUpper().Equals(customerId.ToUpper())); 

     if (employeeId != null) 
      result = result.Where(o => o.EmployeeID.Equals(employeeId)); 

     if (orderDateFrom != null) 
      result = result.Where(o => o.OrderDate >= orderDateFrom); 

     if (orderDateUntil != null) 
      result = result.Where(o => o.OrderDate <= orderDateUntil); 

     if (requiredDate != null) 
      result = result.Where(o => o.RequiredDate == requiredDate); 

     if (shippedDate != null) 
      result = result.Where(o => o.ShippedDate == shippedDate); 

     return result.ToList(); 
    } 

當代碼執行查詢（result.ToList（）），它拋出異常。如果我刪除datetime.Where子句，它工作正常。

謝謝！

解決方案

我已經改變了我的代碼：

public IList<Order> GetOrders(int? orderId = null, string customerId = null, int? employeeId = null, DateTime? orderDateFrom = null, DateTime? orderDateUntil=null, DateTime? requiredDate = null, DateTime? shippedDate = null) 
    { 
     IQueryable<Order> result; 

     result = from order in ctx.Orders.Include("Order_Details") 
       select order; 

     // Apply filters to the base query 
     if (orderId != null) 
      result = result.Where(o => o.OrderID.Equals(orderId.Value)); 

     if (!String.IsNullOrEmpty(customerId)) 
      result = result.Where(o => o.CustomerID.ToUpper() == customerId.ToUpper()); 

     if (employeeId != null) 
      result = result.Where(o => o.EmployeeID == employeeId.Value); 

     if (orderDateFrom != null) 
      result = result.Where(o => o.OrderDate >= orderDateFrom.Value); 

     if (orderDateUntil != null) 
      result = result.Where(o => o.OrderDate <= orderDateUntil.Value); 

     if (requiredDate != null) 
      result = result.Where(o => o.RequiredDate == requiredDate.Value); 

     if (shippedDate != null) 
      result = result.Where(o => o.ShippedDate == shippedDate.Value); 

     return result.ToList(); 
    } 

如果有人有更好的解決方案，請讓我知道。

Answer 1

您正在使用可空類型的DateTime？在你的例子中。我不確定您的數據庫列是否允許爲NULL，但我會使用date.Value來傳遞參數的值以確保EF不會超出它。請注意，對於可爲空的類型，您可以使用HasValue屬性來檢查您的參數是否包含適當的值。這導致：

if (orderDateFrom.HasValue) 
    result = result.Where(o => o.OrderDate >= orderDateFrom.Value);