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C# Entity Framework Basics LINQ Queries Sorting a Query

Posted by Amy Shah
Amy Shah
25,337 Points

In Repository.cs update the GetCourses method to sort the list of available courses by the teacher's last name and then

I need help because this is not compiling. I have reviewed that I need to orderby last name thenby first name. I think there is a syntax error

Course.cs 
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Treehouse.CodeChallenges
{
    public class Course
    {
        public Course()
        {
            Students = new List<CourseStudent>();
        }

        public int Id { get; set; }
        public int TeacherId { get; set; }
        [Required, StringLength(200)]
        public string Title { get; set; }
        public string Description { get; set; }
        public int Length { get; set; }

        public Teacher Teacher { get; set; }
        public ICollection<CourseStudent> Students { get; set; }
    }
}
Repository.cs 
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;

namespace Treehouse.CodeChallenges
{
    public static class Repository
    {
        public static List<Course> GetCourses()
        {
            using (var context = new Context())
            {
                return context.Courses.ToList()
                              .Where(c => c.Teacher.LastName == lastName)
                              .OrderBy(c => c.Teacher.LastName)
                              .ThenBy(c => c.Teacher.FirstName)
                              .ToList();
            }
        }

        public static List<Course> GetCoursesByTeacher(string lastName)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Where(c => c.Teacher.LastName == lastName)
                              .ToList();
            }
        }
    }
}
Teacher.cs 
namespace Treehouse.CodeChallenges
{
    public class Teacher
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

2 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You're pretty close, but:

  • you should only call ToList() once, at the end of the LINQ expression
  • the challenge did not ask you to filter the list
  • there's no lastName parameter defined in this method to use in filtering anyway
Steven Scott
Steven Scott
7,542 Points
Steven Scott
Steven Scott
7,542 Points

This passed for me.

using System.Collections.Generic; using System.Data.Entity; using System.Linq;

namespace Treehouse.CodeChallenges { public static class Repository { public static List<Course> GetCourses() { using (var context = new Context()) { return context.Courses.ToList(); } }

    public static List<Course> GetCoursesByTeacher(string lastName)
    {
        return null; // TODO
    }
}

}

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

That's not a valid solution. If the challenge accepted it, you have discovered a bug in the evaluation mechanism.