var data = from employee in contexthelper.BsEmployee
join position in
(
from employee_position in contexthelper.Employee_Position.Where(n => n.IsDisabled == false)
join
position in contexthelper.Position on employee_position.PositionID equals position.PositionId
select new
{
PositionName = position.PositionName,
Employee_Id = employee_position.Employee_Id
}
)
on employee.employee_id equals position.Employee_Id into leftjoin1
from position in leftjoin1.DefaultIfEmpty()
join dept in contexthelper.BsDept on employee.DeptId equals dept.DeptId into leftjoin2
from dept in leftjoin2.DefaultIfEmpty()
join duty in contexthelper.BsDuty.Where(n => n.worker_sign == false) on employee.f_duty_id equals duty.duty_id into leftjoin3
from duty in leftjoin3.DefaultIfEmpty()
join department in contexthelper.BsDepartment on employee.f_dpt_id equals department.dpt_id into leftjoin4
from department in leftjoin4.DefaultIfEmpty()
join subdpt in contexthelper.BsSubdpt on employee.f_subdpt_id equals subdpt.sub_id into leftjoin5
from subdpt in leftjoin5.DefaultIfEmpty()
where employee.f_leave_sign == false && employee.id > MaxID
select new EmployeeModel
{
ID = employee.id,
UserNo = employee.employee_id,
UserName = employee.f_per_name,
Dept = dept == null ? "" : dept.DeptName,
SubDept = subdpt == null ? "" : subdpt.sub_dptname,
Duty = duty == null ? "" : duty.duty_name,
Position = position == null ? "" : position.PositionName
};
提示 DbIsNullExpression 的参数必须引用基元类型或引用类型。
------解决思路----------------------
三目中的null判断对应的IsNull()只适用于字段，而不适用于左连接产生的对象
你的问题，应该通过
rom duty in leftjoin3.DefaultIfEmpty({new Duty {DeptName = ""})
其他的DefaultIfEmpty也是类似
然后最终的Select中直接Dept = dept.DeptName即可，不需要判断了，因为dept在关联为空时，结果中会自动使用new Duty {DeptName = ""}这个对象
------解决思路----------------------
.DefaultIfEmpty(null)对于引用类型跟.DefaultIfEmpty()没有区别
你必须手动构造一个对象作为无关联时的默认值