在 Linq 中加入、分组和求和答案

【问题标题】：Join, Group by and Sum in Linq在 Linq 中加入、分组和求和
【发布时间】：2022-01-22 21:38:48
【问题描述】：

我想通过employeeId 对员工的加班时间进行分组，并获取employeeNames 和员工每月加班总时长的数据。但是这个 Linq 查询给出了翻译错误。

var results = 
    from overtime in context.Overtimes
    join employeeCredential in context.EmployeeCredentials
        on overtime.EmployeeId equals employeeCredential.id
    join employeeDetail in context.EmployeeDetails
        on employeeCredential.id equals employeeDetail.employeeId
    where overtime.Month == month && overtime.Year == year
    group new { overtime, employeeCredential, employeeDetail } by overtime.EmployeeId into g
    select new MonthlyOvertimeWorkHours
    {
        EmployeeName = g.First().employeeDetail.employeeName,
        TotalWorkHourOfMonth = g.Sum(t => t.overtime.OvertimeWorkHour)
    };

错误

{ "error": employeeCredential\r\n IsNullable: True\r\n , \r\n employeeDetail = EntityShaperExpression: \r\n EntityType: EmployeeDetail\r\n ValueBufferExpression: \r\n ProjectionBindingExpression: employeeDetail\r\n IsNullable: True\r\n }\r\n .Select(s => s.employeeDetail.employeeName)\r\n .First()' 可以不被翻译。要么重写查询形式，翻译，或通过插入显式切换到客户端评估调用“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或 'ToListAsync'。 }

【问题讨论】：

它给出了什么错误？
“错误和失败”，400 美元：“这个查询给出了什么翻译错误？”
{ "error": employeeCredential\r\n IsNullable: True\r\n , \r\n employeeDetail = EntityShaperExpression: \r\n EntityType: EmployeeDetail\r\n ValueBufferExpression: \r\ n ProjectionBindingExpression: employeeDetail\r\n IsNullable: True\r\n }\r\n .Select(s => s.employeeDetail.employeeName)\r\n .First()' 无法翻译。以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的调用显式切换到客户端评估。 }

标签： c# linq

【解决方案1】：

在 EF Core 6 之前，您无法在分组后访问记录（这通常很糟糕）。只有聚合和Key 可用。

要解决问题，只需将employeeName 添加到分组键。

var results = 
    from overtime in context.Overtimes
    join employeeCredential in context.EmployeeCredentials
        on overtime.EmployeeId equals employeeCredential.id
    join employeeDetail in context.EmployeeDetails
        on employeeCredential.id equals employeeDetail.employeeId
    where overtime.Month == month && overtime.Year == year
    group new { overtime, employeeCredential, employeeDetail } by new { overtime.EmployeeId, employeeDetail.employeeName } into g
    select new MonthlyOvertimeWorkHours
    {
        EmployeeName = g.Key.employeeName,
        TotalWorkHourOfMonth = g.Sum(t => t.overtime.OvertimeWorkHour)
    };

【讨论】：