Question

我有以下课程

public class School
{
    public List<Student> Students { get; set; }
    public List<Teacher> Teachers { get; set; }
}

现在我有此方法

public bool Evaluate(??)
{
    var school = DbContext.Schools.FirstOrDefault();
    return school.??.Any(/*some expresions*/)
}

我应该能够在??中传递一个值并使用它，以便我可以同时使用

return school.Students.Any(/*some expresions*/)
return school.Teachers.Any(/*some expresions*/)

那么我该如何用学生或老师替换问号？

编辑：

public class Student 
{
    public string FullName { get; set; }
    public bool Registered { get; set; }
    public bool Passed { get; set; }
}

public class Teacher
{
    public string FullName { get; set; }
    public bool CanEvaluate { get; set; }
    public bool Validator { get; set; }
}


public class DynamicCheckTest
{
    public bool MyExpression<T>(List<T> items, string name,
        Expression<Func<T, bool>> expression)
    {
        return items.Any(x => expression.Compile()(x));
    }
}

public static bool Check<T>(this List<T> items, Func<T, bool> compiledExp)
{
    return items.Any(x => compiledExp(x));
}

Students.Check(x => x.Name == "Mike" &&  x.Registered); // example
Teachers.Check(x => x.Name == "Jack" &&  x.CanEvaluate);// example

现在我必须通过既有学生又有老师的学校但是我不知道会提前打电话给谁

Answer 1

解决“将属性名称作为参数传递”的请求，您可以使用反射，但是我认为这不是一个好方法。相反，可以使用Func<School, List<TElement>>选择所需的List<>属性进行评估...

public bool Evaluate<TElement>(Func<School, List<TElement>> listSelector)
    where TElement : Person
{
    School school = DbContext.Schools.FirstOrDefault();
    DateTime today = DateTime.Today;

    return listSelector(school)
        // For example, check if today is the birthday of anyone in the selected list
        .Any(person => person.DateOfBirth.Month == today.Month && person.DateOfBirth.Day == today.Day);
}

正如@Enigmativity指出的那样，type constraint对于将很多有意义的条件传递给Any()是必要的，Student还假定/要求Teacher和public abstract class Person { public DateTime DateOfBirth { get; } } public class Student : Person { } public class Teacher : Person { }有共同的血统，像这样...

List<>

然后您将使用lambda expression指定所需的bool isAnyStudentsBirthday = Evaluate(school => school.Students); bool isAnyTeachersBirthday = Evaluate(school => school.Teachers); ...

Any()

只要您希望Person考虑的成员以受约束的类型（即Student）可用，此方法就会起作用。如果您想使用特定于Teacher或List<>类的成员进行过滤，则最好的选择是使用类似@Enigmativity's answer的方法，其中过滤器本身是一个参数并接收相同的参数派生类型作为选定的Evaluate()存储。

请注意，如果您想将School与List<>的某些其他集合属性一起使用，而这些属性不是专门为Any()而设计的，或者只是知道所有IEnumerable<>的需求就是Func<>，您可以将Func<School, IList<TElement>> Func<School, ICollection<TElement>> Func<School, IEnumerable<TElement>>的返回类型（最后type parameter）更改为限制较少的内容...

function sell_below10() {
    return Close < HHV(High,20) * 0.9;
}

function sell_abv10() {
    return Close < HHV(High,20) * 0.8;
}

Buy = Cross(Close, MA(Close, 50));

openPrice = Ref(Close, -BarsSince(Buy));
pctChange = IIf(openPrice == 0, 0, (openPrice - Close) / openPrice) * 100;

Sell = IIf(pctChange > 10, sell_abv10(), IIf(pctChange < 10, sell_below10(), False));

Answer 2

您可以使用此方法：

public bool Evaluate<T>(Func<School, List<T>> project, Func<T, bool> filter)
{
    var school = DbContext.Schools.FirstOrDefault();
    return project(school).Any(filter);
}

如果我们假设Student和Teacher的实现是这样的：

public class Student
{
    public string Name;
}

public class Teacher
{
    public string Subject;
}

然后您可以执行以下操作：

bool hasFred = Evaluate(school => school.Students, student => student.Name == "Fred Nerk");
bool teachArt = Evaluate(school => school.Teachers, teacher => teacher.Subject == "Art");

传递属性名称作为参数

2 个答案: