c# - 转换为值类型 'Int32' 失败

Question

我有以下代码。我收到错误:

The cast to value type 'System.Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.

var productItem =   from sales 
                      in db.Sales_inv_details
                  select new { 
                           sales.Sales_Invoices.Customer.Cust_Id, 
                           sales.Sales_Invoices.Customer.Customer_Name,         
                           sales.Sales_Invoices.Employe.Emp_Name, 
                           sales.Sales_Invoices.Employe.Emp_code,
                           sales.Sales_Invoices.Date_invoice, 
                           sales.Item.Item_ID, 
                           sales.Qty, 
                           sales.Qty_Price, 
                           sales.Item.Item_Name, 
                           sales.Item.Item_Code, 
                           Unit_Measure = sales.Item.TBL_Unit_Measure.Code,
                           sales.Sales_Invoices.Descrption, 
                           sales.disc };

productItem = productItem
  .Where(x => (x.Date_invoice >= model.Fromdate & x.Date_invoice <= (model.Todate)));

productItem = productItem
  .Where(x => (x.Emp_code == model.Emp_code));

Answer 1

听起来您的模型将其中一个属性定义为不可为空，但数据库将相应的列设置为可为空，并且其中有一个空值。当生成的阅读器尝试填充模型时，BOOM。不幸的是，我们无法告诉您是哪个属性，它甚至不需要是该代码中提到的属性之一，因为它可能是 FrobNumber。任何属性(property)Sales_inv_details代表。

您需要非常仔细地检查您的模型。从任何属性/列开始 Sales_inv_details代表。当您发现不匹配时:将其标记为可为空，然后重试。