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 SUM 列（Localamount）。

我使用十进制而不是 float

但是我在转换为十进制

的代码时收到错误

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.

 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;

    }

我在以下帖子中尝试了一些选项，但没有运气。

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

我建议您在查询完成后进行演员

var somevar = (decimal)transactions.YourValue

Answer 3

有时需要施放，如果超过两个十进制宫殿

     double TotalQty;
     double.TryParse(sequence.Sum(x => x.Field<decimal>("itemQty")).ToString(),out TotalQty);

Answer 4

如果您不太喜欢调用AsEnumerable，则可以通过一些数学将其转换为int而不是十进制。

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

每个零实际上代表转换将具有的精度。

从this得到了这个答案。只需看一下文件末尾即可。

LINQ to Entities查询不支持强制转换为Decimal

4 个答案: