c# - 具有安全转换和空验证的 Linq

Question

给定代码:

from i in this.GridViewFoo.SelectedItems
select new EmployeeEntity
{
    EmployeeID = (i as EmployeeDto).EmployeeID,
    Email = this.GetAllEmail((i as EmployeeDto).Email, (i as EmployeeDto).SecondaryEmails),
    EmployeeNumber = (i as EmployeeDto).EmployeeNumber,
    FirstName = (i as EmployeeDto).FirstName,
    LastName = (i as EmployeeDto).LastName
}

安全转换后 (i as EmployeeDto) 我可能会收到 NullReferenceException。我如何确保代码的安全性，而不是让他因大量空检查而重载？

解决方案概述:

我做了一些测试来断言这些解决方案是否有效。两者都运行良好并带来相同的结果，您可以查看 HERE .之后我用 OfTypeSolution 做了一些性能测试和 letSolution .

由于 OfType 解决方案的平均时间更好，这就是答案!

Answer 1

您可以使用 OfType在 Select 之前:

from i in this.GridViewFoo.SelectedItems.OfType<EmployeeDto>()
select new EmployeeEntity
{
    EmployeeID = i.EmployeeID,
    Email = this.GetAllEmail(i.Email, i.SecondaryEmails),
    EmployeeNumber = i.EmployeeNumber,
    FirstName = i.FirstName,
    LastName = i.LastName
}

它只会为您提供 SelectedItems 中的 EmployeeDto 类型的项目，因此无需强制转换和空值检查。