在具有多个连接的 Linq 查询中对列进行分组时遇到问题

Question

我有一个想要传递给 Razor 视图的 MVC ViewModel。在控制器中，我创建了一个数据库上下文并使用 Linq 将表连接在一起。汇总和分组后，出现错误：

错误 CS1061 'decimal' 不包含 'GroupBy' 的定义，并且找不到接受第一个参数类型为 'decimal' 的可访问扩展方法 'GroupBy'（您是否缺少 using 指令或程序集引用？

我已经浏览了几乎所有关于堆栈溢出和 google 的示例，但找不到与我的查询结构相匹配的示例。另外，MS 的例子很琐碎，用处不大。

这是控制器中的操作：

public IHttpActionResult GetEmployeeReleasedAllocatedBonus(int eid)
    {
        var employeeReleasedAllocatedBonus =
            (from br in _context.BonusReleases
                join emp in _context.Employees
                    on new
                    {
                        br.EmployeeID,
                        empID = br.EmployeeID
                    } equals new
                    {
                        emp.EmployeeID,
                        empID = eid
                    }
                join job in _context.Jobs on br.JobID equals job.JobID
                join bonus in _context.Bonus
                    on new
                    {
                        br.JobID,
                        empID = br.EmployeeID
                    }
                    equals new
                    {
                        bonus.JobID,
                        empID = bonus.EmployeeID
                    }
                select new EmployeeAllocatedReleasedBonusViewModel()
                {
                    AllocatedToEmployee = br.Amount, AllocatedPercentage = bonus.Amount * 100
                    ,
                    JobNumber = job.JobNumber, JobDescription = job.JobDescription

                })
            .ToList()
            .Sum(s => s.AllocatedToEmployee)
            .GroupBy(g => new {g.JobNumber, g.JobDescription, g.AllocatedPercentage});

        return Ok(employeeReleasedAllocatedBonus);
    }

值得一提的是，AllocatedPercentage 数据类型是小数。但是，我尝试将其更改为字符串，但错误消息仍然存在。

还尝试在 .ToList() 之前使用组功能，但这也不起作用。

Answer 1

在ToList() 之后你有一个List<EmployeeAllocatedReleasedBonusViewModel>。

在Sum(s => s.AllocatedToEmployee) 中，每个s 是一个EmployeeAllocatedReleasedBonusViewModel。显然EmployeeAllocatedReleasedBonusViewModel 有一个属性AllocatedToEmployee，它可能是十进制类型。这可以加到一位小数。

Sum（十进制）的结果是您的GroupBy 的输入。十进制类型是否有方法GroupBy？当然不是！

可惜你忘了告诉我们你的要求。很难从不符合您要求的代码中提取它们。

在我看来，你有两个一对多的关系：

• Employees 有零个或多个 BonusReleases。每个BonusRelease 使用外键恰好属于一个Employee
• Jobs 有零个或多个 BonusReleases。每个BonusRelease 都只属于一个Job。

现在你想要什么：你想要所有JobNumbers 和JobDescriptions 中的所有Jobs 以及它们的AllocatedPercentage 的总数吗？我不确定Employees 在这个查询中做了什么。

当您想要带有子项的项目时，例如带有学生的学校、带有订单的客户、带有 OrderLine 的订单，请使用 GroupJoin。如果您希望反过来：学生与他就读的学校，向下订单的客户订购，使用加入。

var result = dbContext.Jobs.GroupJoin(dbContext.BonusReleases,
    job => job.Id,                       // from every Job take the primary key
    bonusRelease => bonusReleas.JobId,   // from every BonusRelease take the foreign key

    // parameter ResultSelector: take every Job with all its BonusReleases to make a new:
    (job, bonusReleasesOfThisJob) => new
    {
        JobNumber = job.JobNumber,
        JobDescription = job.JobDescription

        // do you want the total of all allocated percentages?
        TotalAllocatedPercentages = bonusReleasesOfThisJob
            .Select(bonus => bonus.Amount)
            .Sum(),
            // do something to make it a percentage

         // or do you want a sequence of allocated percentages?
         TotalAllocatedPercentages = bonusReleasesOfThisJob
            .Select(bonus => bonus.Amount)
            .ToList(),
});

或者您想要 JobNumber/JobDescription/每位员工分配的奖金总额？

var result = dbContext.Employees.GroupJoin(dbContext.BonusReleases,
    employee => employee.Id,    // from every Employee take the primary key
    bonus => bonus.EmployeeId,  // from every BonusRelease take the foreign key

    (employee, bonusesOfThisEmployee) => new
    {
        // Employee properties:
        EmployeeId =  employee.Id,
        EmpoyeeName = employee.Name,

        // for the jobs: Join the bonusesOfThisEmployee with the Jobs:
        Jobs = dbContext.Jobs.GroupJoin(bonusOfThisEmployee,
            job => job.Id,
            bonusOfThisEmployee => bonusOfThisEmployee.JobId,

            (job, bonusesOfThisJob) => new
            {
                Number = job.Id,
                Description = job.Description,
                TotalBonus = bonusOfThisJob.Select(bonus => bonus.Amount).Sum(),
            }),
   });               

Answer 2

Harald 的评论很关键 - 在 ToList() 之后，我有一个 .因此，我退后一步说，如果我先将结果放入匿名对象中会怎样。然后进行分组，然后求和，将最终结果放入视图模型中。有效。这是答案。

var employeeReleasedAllocatedBonus =
            (from br in _context.BonusReleases
                join emp in _context.Employees
                    on new
                    {
                        br.EmployeeID,
                        empID = br.EmployeeID
                    } equals new
                    {
                        emp.EmployeeID,
                        empID = eid
                    }
                join job in _context.Jobs on br.JobID equals job.JobID
                join bonus in _context.Bonus
                    on new
                    {
                        br.JobID,
                        empID = br.EmployeeID
                    }
                    equals new
                    {
                        bonus.JobID,
                        empID = bonus.EmployeeID
                    }
                select new 
                {
                    AllocatedToEmployee = br.Amount
                    ,AllocatedPercentage = bonus.Amount * 100
                    ,JobNumber = job.JobNumber
                    ,JobDescription = job.JobDescription
                })
                .GroupBy(g => new {g.JobNumber, g.JobDescription, g.AllocatedPercentage})
                .Select(t => new EmployeeAllocatedReleasedBonusViewModel
                {
                JobNumber = t.Key.JobNumber,
                JobDescription = t.Key.JobDescription,
                AllocatedPercentage = t.Key.AllocatedPercentage,
                AllocatedToEmployee = t.Sum(ae => ae.AllocatedToEmployee)
                });