返回匿名类型作为强类型

Question

I am writing a method in C# class. It is using Database Linq query. I want it's result to be returned by method. I am using the following code but it is resulting in error;

class getCourses
{
    public string  Courseid { get; set; }
    public string CourseName { get; set; }
}

public List<getCourses>  GetCourses()
    {
        List<getCourses> L_courses = new List<getCourses>();
        L_courses = (from Cr in _er.Courses
                            select new
                            {
                                Courseid = Cr.CourseID,
                                CourseName = Cr.CourseName,
                            }).ToList();
    }

Answer 1

You are creating a list of anonymous types.You should create a strongly typed list which is List<getCourses> according to your return type. Change select new to select new getCourses . Also creating another variable for list ( L_courses ) is completely unnecessary, you can just return the list directly if you are not planning to do anything with your list before return.

Answer 2

You have to tell it which class to use, not create an anonymous type:

public List<getCourses> GetCourses()
{
    return (from Cr in _er.Courses
            select new getCourses
                   {
                       Courseid = Cr.CourseID,
                       CourseName = Cr.CourseName,
                   }).ToList();
}

Answer 3

Well

new {  
   Courseid = Cr.CourseID, 
   CourseName = Cr.CourseName, }

is an Anonymous type (just because the fields matches getCourses doesn't mean it is a getCourses ). You can verify the type returned using intelisense by putting your cursor over .ToList() . You probably should use:

new getCources() {  
   Courseid = Cr.CourseID, 
   CourseName = Cr.CourseName, }

Answer 4

Two answers.

First (piggy backing on other answers) you can write:

public List<getCourses>  GetCourses() {
    return _er.Courses.Select(c => 
        new getCourses {
             Courseid = c.CourseID,
             CourseName = c.CourseName
        }).ToList();
}

Second way... Since _er.Courses is already the object that you are wanting to deal with, why not something like this... Suppose _er.Courses is a list of Course objects. Then you can do:

public Course : ICourseOverview {
    // properties
}

public interface ICourseOverview {
    public int CourseId { get; }
    public string CourseName { get; }
}

Then you can simply do something like:

public IEnumerable<ICourseOverview> GetCourses() {
    return (IEnumerable<ICourseOverview>)_er.Courses;
}

But if you did that, then it is debatable what the point of this class is (depending on the scope that the application has on _er and _er.Courses).