Question

有人可以将此查询翻译成Linq吗？此查询计算员工的出勤人数。

select 
    count(attandance.empid),
    employee2.empname 
from 
    employee2
inner join 
    attandance 
    on employee2.empid=attandance.empid
group by 
    employee2.empname

Answer 1

这应该会得到与sql相同的结果。如果您使用linq到sql或EF，只需用数据源替换两个List。

        List<Employee2> employee2 = new List<Employee2>
        {
            new Employee2 { EmpId = 1, EmpName = "Bob" },
            new Employee2 { EmpId = 2, EmpName = "Sam" },
            new Employee2 { EmpId = 3, EmpName = "Jim" },
        };

        List<Attendance> attandance = new List<Attendance>
        {
            new Attendance { EmpId = 1 },
            new Attendance { EmpId = 2 },
            new Attendance { EmpId = 2 },
            new Attendance { EmpId = 3 },
            new Attendance { EmpId = 3 },
            new Attendance { EmpId = 3 },
        };

        var r = from emp in employee2
                join att in attandance on emp.EmpId equals att.EmpId
                group emp by emp.EmpName into g
                select new { EmpName = g.Key, Count = g.Count() };

Answer 2

这应该有效：

var attendance = (from e in db.employee2 // db would be your datacontext
                  select new 
                  {
                     empName = e.empname,
                     attendanceCount = (from a in db.attandance
                                        where a.empid == e.empid).Count()
                  });

如果您不想使用datacontext，可以通过连接数据源在linqpad中尝试上述linq。

查询Linq计数

2 个答案: