无法将类型泛型列表隐式转换为类

Question

I want to list courses and list semesters for every course.

Here is my code

public List<Course> GetAllCourses()
    {
        IList<App> app = App.GetAll();
        List<CInstance> ci = new List<CInstance>();

        for (int i = 0; i < app.Count; i++)
        {
            ci.Add(CInstance.GetInstance(app[i].Id));
        }

        return ci.Select(c => new Course
        {
            CourseId = c.Course.CourseId,
            Semester = ci.Select(s => new Semester
            {
               SemesterId  = c.Course.Semester.SemesterId
            }).ToList()
        }).ToList();
    }

I get Cannot implicitly convert type System.Collection.Generic.List<Test.Semester> to Test.Semester

Can someone please correct this code for me?

Update

I'm exporting to JSON. So, it will be look like this

[
- {
   courseId: 123,
   courseName: "someCouse",
   semester:
   - {
      semesterId:26
   },
   - {
      semesterId:27
   }
}
]

Answer 1

您尚未显示代码，但我认为您的Semester属性为Test.Semester类型，其中应为List<Semester>类型（或更好的IList<Semester> ）。

Answer 2

Depends on what you're trying to do. If it would only have a single semester, instead of

 Semester = ci.Select(s => new Semester
            {
               SemesterId  = c.Course.Semester.SemesterId
            }).ToList() 

You could use FirstOrDefault() like

 Semester = ci.FirstOrDefault(s => new Semester
            {
               SemesterId  = c.Course.Semester.SemesterId
            })

If it's possible that it's in more than 1 semester, you'll need to change your Semester type to be a list.

Answer 3

If you want to get a proper JSON-document with an array of Semester you'll have to edit the Course -class, so that the property Semester is a List<Semester> instead of Semester .

Example:

public class Course
{
    public int CourseID { get; set; }
    public string CourseName { get; set; }
    public List<Semester> Semester { get; set; }
}

If your Course -class looks like that, you should be able to run the rest of your function without any changes.