Linq的三元运算符 [英] Ternary operator in Linq

问题描述

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,
                         };

有没有一种方法不重复previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault()逻辑来选择Salary值?

Is there a way not to repeat the previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault() logic to pick Salary value?

我尝试过:

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

但是，如果previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault()为null，则会引发异常.

But, if previousMonthPayroll.Where(t => t.EmployeeId == payroll.EmployeeId).FirstOrDefault() is null, it throws exception.

推荐答案

从所有答案中可以看出，有几种方法可以做到这一点，我的首选方法是:

As witnessed by all of the answers, there are several ways of doing this, my preferred way would be:

var result = from payroll in currentMonthPayroll
             select new SalaryDifference
             {
                 PreviousMonthSalary = previousMonthPayroll
                     .Where(t => t.EmployeeId == payroll.EmployeeId)
                     .Select(prev => prev.Salary)
                     .FirstOrDefault()
             };

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