使用 LINQ 转换为 Int

Question

下面LINQ有几个Convert.ToInt32方法。但这不起作用。参考互联网，使用的是int.Parse而不是转换。仍然给出错误。请告诉我执行此操作的方向。

在下面的查询中，tody数据类型是DateTime

var ds = (from a in dbSetInvHeader
          join b in dbSetCustomer on a.BusinessEntityID equals b.Id
          join c in dbSetFinancialInfo on b.Id equals c.Id
          where (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount) > 0
                      && DbFunctions.AddDays(a.InvoiceDate, Convert.ToInt32(c.CreditPeriod)) >= tody
          select new OverDueInvoices
                      {
                          CustomerName = b.Name,
                          InvoiceNo = a.InvoiceNo,
                          InvoiceAmount = a.TotalAmount - a.ApplyToInvoiceCreditAmount,
                          DueAmount = (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount),
                          CreditAmount = a.ApplyToInvoiceCreditAmount,
                          NoOfDays = Convert.ToInt32(DbFunctions.DiffDays(tody, a.InvoiceDate))
                      }).ToList();

更新 ：

该代码使用实体框架来处理上述 LINQ 抛出错误：

使用时Convert.ToInt32：

“LINQ to Entities 无法识别‘Int32 ToInt32(System.Decimal)’方法，并且该方法无法转换为存储表达式。”

使用时int.Parse：

“LINQ to Entities 无法识别‘Int32 Parse(System.String)’方法，并且该方法无法转换为存储表达式。”

Answer 1

SQL 不知道 Convert.ToInt32 函数。实体框架中似乎没有将字符串转换为 int 的解决方法。您可以做的就是向对象 NoOfDaysString 添加另一列

public string NoOfDaysString {get; set;}
public string NoOfDays {get { return  Convert.ToInt32(NoOfDaysString); } ;}

并重写您的查询

var ds = (from a in dbSetInvHeader
                  join b in dbSetCustomer on a.BusinessEntityID equals b.Id
                  join c in dbSetFinancialInfo on b.Id equals c.Id
                  where (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount) > 0
                  && DbFunctions.AddDays(a.InvoiceDate, Convert.ToInt32(c.CreditPeriod)) >= tody
                  select new OverDueInvoices
                  {
                      CustomerName = b.Name,
                      InvoiceNo = a.InvoiceNo,
                      InvoiceAmount = a.TotalAmount - a.ApplyToInvoiceCreditAmount,
                      DueAmount = (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount),
                      CreditAmount = a.ApplyToInvoiceCreditAmount,
                      NoOfDaysString = Convert.ToInt32(DbFunctions.DiffDays(tody, a.InvoiceDate))

                  }).ToList();

这是我能想到的 where 语句的唯一解决方法。在对象中添加 CreditPeriod 并在对象进入内存后执行 where

var ds = (from a in dbSetInvHeader
              join b in dbSetCustomer on a.BusinessEntityID equals b.Id
              join c in dbSetFinancialInfo on b.Id equals c.Id
              where (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount) > 0
              select new OverDueInvoices
              {
                  CustomerName = b.Name,
                  InvoiceNo = a.InvoiceNo,
                  InvoiceAmount = a.TotalAmount - a.ApplyToInvoiceCreditAmount,
                  DueAmount = (a.TotalAmount - a.AppliedAmount - a.ApplyToInvoiceCreditAmount),
                  CreditAmount = a.ApplyToInvoiceCreditAmount,
                  NoOfDaysString = Convert.ToInt32(DbFunctions.DiffDays(tody, a.InvoiceDate))
                  CreditPeriod = c.CreditPeriod
              })ToList().Where(t=>Convert.ToInt32(t.CreditPeriod) >= NoOfDays).ToList();