Question

在where子句中获取orderby的此错误。我之所以这样做，是因为之前，如果我没有定义'人'，我会在返回时收到错误，因为人们说这个名字'人'在当前的情境中并不存在。我该如何解决这个问题？

 public JsonResult PersonsList(string birthyear)
 {
     TutorialDBContext db = new TutorialDBContext();
     var NumericYear = Convert.ToInt32(birthyear);
     IQueryable people;

     if (birthyear == "All")
     {
          people = from m in db.persons
                   select m;

          people = people.OrderByDescending(s => s.birthdate);
     }
     else
     {
          people = from m in db.persons
                   where m.birthdate.Year >= NumericYear
                   where m.birthdate.Year <= (NumericYear + 9)
                   select m;
     }

     return Json(people, JsonRequestBehavior.AllowGet);
 }

Answer 1

因为确实没有这样的方法。虽然有一个接受IQueryable<T>。使用

IQueryable<Person> people;

或任何适合的元素类型。

Answer 2

OrderByDescending()是 IQueryable<T> 的扩展方法，而不是非通用IQueryable的扩展方法。

因此，您需要将people声明为IQueryable<Person>。

Answer 3

如上所述，您需要将people声明为IQueryable<Person>或从People表返回的类型。如果你想使用隐式类型，你可以重新排列代码：

var people = from m in db.persons
             select m;
if (birthyear == "All")
{
    people = people.OrderByDescending(s => s.birthdate);
}
else
{
     people = people.Where(p => p.birthdate.Year >= NumericYear
                             && p.birthdate.Year <= NumericYear + 9)
}

Answer 4

您必须在代码文件的开头有using System.Linq;。
您应该将IQueryable people;更改为IQueryable<Person> people;
如果您将此方法称为All作为birthyear值，则会在到达var NumericYear = Convert.ToInt32(birthyear);

我建议将整个功能更改为

public JsonResult PersonsList(string birthyear)
{
    using (var db = new TutorialDBContext())
    {
        IQueryable<Person> people;

        if (birthyear == "All")
        {
            people = db.persons.OrderByDescending(s => s.birthdate);
        }
        else
        {
            var NumericYear = Convert.ToInt32(birthyear);
            people = from m in db.persons
                where m.birthdate.Year >= NumericYear
                where m.birthdate.Year <= (NumericYear + 9)
                select m;
        }

        return Json(people, JsonRequestBehavior.AllowGet);
    }
}

'IQueryable'不包含'OrderByDescending'的定义

4 个答案: