Linq Group通过C＃.net

Question

1. 我创建了一个Emp类

   class Emp
   {
       public Emp()
       {
       }
       public Emp(Int64 empId, string empName, double empSalary,int empDeptId)
       {
           this.EmpID = empId;
           this.EmpName = empName;
           this.EmpSalary = empSalary;
           this.EmpDeptId = empDeptId; 
       }
       public Int64 EmpID { get; set; }
       public string EmpName { get; set; }
       public double EmpSalary { get; set; }
       public Int32 EmpDeptId { get; set; }
   }
   

2. 我只是按命令将组应用到EmpList然后在return语句中我得到运行时异常

  

ConsoleApplication5.exe中出现未处理的“System.InvalidCastException”类型异常

其他信息：

  

无法转换类型为'WhereSelectEnumerableIterator 2[System.Linq.IGrouping 2 [System.Int32，ConsoleApplication5.Emp]，＆lt;＆gt; f__AnonymousType0 3[System.Int32,System.Double,System.Double]]' to type 'System.Collections.Generic.IEnumerable 1 [ConsoleApplication5.EmpGroup]'的对象。

我也分享了我写的代码。

public IEnumerable<EmpGroup> GroupByDeptId()
        {

            var numberGroups =from result in empList
                              group result by result.EmpDeptId into groupingData
                              select new 
                              {
                                  EmpDeptId = groupingData.Key,
                                  SalarySum = groupingData.Sum(p => p.EmpSalary),
                                  AverageSalary = groupingData.Average(p => p.EmpSalary) 
                              };

               return (IEnumerable<EmpGroup>)numberGroups;

        }

`3。我还为EmpGroup创建了一个类来处理分组数据。

class EmpGroup
    {
        public Int32 EmpDeptId { get; set; }

        public double SalarySum { get; set; }

        public double AverageSalary { get; set; }
    }

Answer 1

即使它们具有相同的字段，您也无法从匿名转换为您的类型。您应该编辑LINQ select以创建新的EmpGroup：

public IEnumerable<EmpGroup> GroupByDeptId()
        {

            var numberGroups =from result in empList
                              group result by result.EmpDeptId into groupingData
                              select new EmpGroup() // here
                              {
                                  EmpDeptId = groupingData.Key,
                                  SalarySum = groupingData.Sum(p => p.EmpSalary),
                                  AverageSalary = groupingData.Average(p => p.EmpSalary) 
                              };

               return (IEnumerable<EmpGroup>)numberGroups;

        }