Question

我有以下型号：

public class Person 
{
    long Id;
    string name;
}

public class Student : Person
{
    string studentId;
}

public class Bus
{
    long Id;

    public ICollection<Person> riders {set; get;}
}

public class SchoolBus : Bus
{
    long schoolBusNumber;
}

我还有以下代码：

SchoolBus schoolBus = new SchoolBus();

schoolBus.riders = new List<Person>
{
    new Student { name = "Jim" },
    new Student { name = "Jane }
}


var query = from rider in SchoolBus.riders
    select new 
    {
        (rider as Student).studentId;
    }

学生和人被设置为单独的表，我正在使用DbContext。

我知道为什么这不起作用，但是有什么方法可以让我通过使用Person集合来返回正确的studentId？

Answer 1

试试这个：

var studentIds = rider.OfType<Student>().Select(x => x.studentId);

Answer 2

如果您的代码与您显示的完全相同，则可以使用：

SchoolBus schoolBus = new SchoolBus（）;

schoolBus.riders = new List<Person>
{
    new Student { name = "Jim" },
    new Student { name = "Jane }
}
var query = from rider in SchoolBus.riders
select new 
{
    riderID = (rider as Student).studentId;
}

但是如果您的查询在linq2entity上运行，您应该显示确切的代码和问题。

继承和Linq到实体

2 个答案: