Linq 中的三元运算符

var result = from payroll in currentMonthPayroll
    select new SalaryDifference
    {
        PreviousMonthSalary = previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault() == null ?
        default(decimal) : previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault().Salary,
    };

有没有办法不重复previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault()选择的逻辑Salary value?

I tried:

previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId)
    .FirstOrDefault().Salary ?? default(decimal);

But, if previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault()为 null，则抛出异常。

您可以使用Enumerable.DefaultIfEmpty

previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId)
                    .DefaultIfEmpty(yourDefaultObject)
                    .First();

Where yourDefaultObject是一个默认工资为的对象default(decimal).