使用 “Linq的方法” 与日期时间处理

Question

[ASP.NET 4.0/4.1 EF]

嗨，

我正尝试使用 “Linq的方法” 的基础上日期时间字段来过滤数据源，但我收到错误：“在这种情况下只支持原始类型（如Int32，String和Guid）”。

我知道Entity Framework在处理日期时有一些限制，但我需要的是处理这个问题的一些优雅的解决方案。

我的代码是：

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(); 
    } 

当代码执行查询（result.ToList（）），它抛出异常。如果我删除datetime.Where子句，它工作正常。

谢谢！

解决方案

我已经改变了我的代码：

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决方案，请让我知道。

Answer 1

您正在使用可空类型的DateTime？在你的例子中。我不确定您的数据库列是否允许为NULL，但我会使用date.Value来传递参数的值以确保EF不会超出它。请注意，对于可为空的类型，您可以使用HasValue属性来检查您的参数是否包含适当的值。这导致：

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