Question

请考虑此查询：

from r in ent.MyTable
group r by new { r.EmployeeName, r.EmployeeID } into g
let c = " (" + SqlFunctions.StringConvert((decimal?)g.Count()) + " )"
select new
{
    EmployeeName = g.Key.EmployeeName + c ,
    EmployeeID = g.Key.EmployeeID
});

效果很好。当我想要使用此查询时，我收到错误：

from r in ent.MyTable
group r by new { r.EmployeeName, r.EmployeeID } into g
select new
{
    EmployeeName = g.Key.EmployeeName + " (" + g.Count() + ")",
    EmployeeID = g.Key.EmployeeID
});

错误：

无法将System.Object转换为System.String

我该怎么做？

Answer 1

为什么不对输出进行双重转换？

WEBSITE_RUN_FROM_ZIP

Answer 2

因此，您有一个MyTable，其中表中的每一行（可能是行）至少具有属性EmployeeId和EmployeeName。

您要将表中的行分组为EmployeeId和EmployeeName相等的组。对于每个组，您都希望使用公用的{EmployeeName” +雇员数的形式来使用公用EmployeeId和该组中的雇员数。

var result = ent.MyTable                   // take MyTable
   .GroupBy(employee => new                // group all rows of this table into groups
   {                                       // with equal EmployeeId and EmployeeName
       Id = employee.EmployeeId,
       Name = employee.EmployeeName,
   })
   .Select(group => new                    // from every group make one object
   {                                       // with properties:
       EmployeeId = group.Key.Id,          // - the common employeeId
       EmployeeName = group.Key.Name       // - the common employeeName + the string value 
           + group.Count().ToString(),     //   of the number of elements in the group
   });

消除LET运算符和SqlFunction

2 个答案: