LINQ to Entities查询不支持强制转换为Decimal

Question

我有一个数据库表Transaction(transactionID,LocalAmount ...).其中Localamount属性的数据类型为float.在UI上我试图在按钮单击事件的一行中返回一列SUM(Localamount).

我用过decimal而不是float

但是我在转换为十进制的代码上出现错误

System.NotSupportedException was unhandled by user code
Message=Casting to Decimal is not supported in LINQ to Entities queries, because the required precision and scale information cannot be inferred.

该

 public static IEnumerable<TransactionTotalForProfitcenter> GetTotalTransactionsForProfitcenter(int profitcenterID)
    {
        List<TransactionTotalForProfitcenter> transactions = new List<TransactionTotalForProfitcenter>();
        using (var context = new CostReportEntities())
        {
          transactions = (from t in context.Transactions
                            join comp in context.Companies on t.CompanyID equals comp.CompanyID
                            join c in context.Countries on comp.CountryID equals c.CountryID
                            where c.CountryID.Equals(comp.CountryID) && t.CompanyID == comp.CompanyID 

                            join acc in context.Accounts
                                 on t.AccountID equals acc.AccountID
                            join pc in context.Profitcenters
                                on t.ProfitcenterID equals pc.ProfitcenterID
                            group t by pc.ProfitcenterCode into tProfitcenter

                            select new TransactionTotalForProfitcenter
                            {
                                ProfitcenterCode = tProfitcenter.Key,
                    //the error is occurring on the following line           
                                TotalTransactionAmount = (decimal)tProfitcenter.Sum(t => t.LocalAmount),  
                   //the error is occurring on the following line       
                                TotalTransactionAmountInEUR = (decimal)tProfitcenter.Sum(t => t.AmountInEUR) //the error is occurring on this line 
                            }
                            ).ToList();

        }
        return transactions;

    }

我从以下帖子中尝试了一些选项,但没有运气.

• LINQ to SQL奇怪的浮动行为
• 从Decimal到Float的转换

任何人都可以指出我可能尝试的其他选择.请原谅我对LINQ的一点知识,如果它太琐碎了.

Answer 1

实体框架表明它不支持您想要的转换.一种解决方法是尽可能简单地在数据库中执行尽可能多的工作,然后在内存中完成该过程.在您的情况下,您可以计算其本机类型的总和,将结果作为匿名类型提取到内存中,然后在构建实际需要的类型时执行转换.要获取原始查询,您可以进行以下更改:

select new // anonymous type from DB
{
    ProfitcenterCode = tProfitcenter.Key,
    // notice there are no conversions for these sums
    TotalTransactionAmount = tProfitcenter.Sum(t => t.LocalAmount),       
    TotalTransactionAmountInEUR = tProfitcenter.Sum(t => t.AmountInEUR)
})
.AsEnumerable() // perform rest of work in memory
.Select(item =>
     // construct your proper type outside of DB
    new TransactionTotalForProfitcenter
    {
        ProfitcenterCode = item.ProfitcenterCode,
        TotalTransactionAmount = (decimal)item.TotalTransactionAmount
        TotalTransactionAmountInEUR = (decimal)item.TotalTransactionAmountInEUR
    }
).ToList();

Answer 2

如果您碰巧没有调用 AsEnumerable 的奢侈，那么您可以int使用一些数学方法将其转换为十进制数。

 (((decimal)((int)(x.Discount * 10000))) / 10000)

每个零实际上表示转换将具有的精度。

从这个得到这个答案。只需看看文件的末尾。