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C# Entity Framework Basics CRUD Operations Deleting an Entity

Entity Framework

Question Link: https://teamtreehouse.com/library/entity-framework-basics/crud-operations/deleting-an-entity

Question:
In Repository.cs update the DeleteCourse method to delete a course from the database.
    Instantiate an instance of the Context class within a using statement
    Create a "stub" course entity and set its Id property value to the passed in id parameter value
    Retrieve the course's entry using the context's Entry method and set its state to "Deleted"
    Call the context's SaveChanges method to persist the changes to the database
Provided Code:
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
                              .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();
            }
        }

        public static Course GetCourse(int id)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Include(c => c.Teacher)
                              .SingleOrDefault(c => c.Id == id);
            }
        }

        public static void AddCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Add(course);
                context.SaveChanges();
            }
        }

        public static void UpdateCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Attach(course);
                context.Entry(course).State = EntityState.Modified;
                context.SaveChanges();
            }
        }

        public static void DeleteCourse(int id)
        {
            // TODO
        }
    }
}
My Last Attempt:
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
                              .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();
            }
        }

        public static Course GetCourse(int id)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Include(c => c.Teacher)
                              .SingleOrDefault(c => c.Id == id);
            }
        }

        public static void AddCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Add(course);
                context.SaveChanges();
            }
        }

        public static void UpdateCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Attach(course);
                context.Entry(course).State = EntityState.Modified;
                context.SaveChanges();
            }
        }

        public static void DeleteCourse(int id)
        {
                using (Context context = GetContext())
                var stub = new stub() { Id = stubId };
                context.Entry(stub).State = EntityState.Deleted;

                context.SaveChanges();

        }
    }
}
Error Provided:
Repository.cs(62,54): error CS1023: An embedded statement may not be a declaration or labeled statement
Compilation failed: 1 error(s), 0 warnings

Not sure what I'm doing wrong...

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
                              .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();
            }
        }

        public static Course GetCourse(int id)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Include(c => c.Teacher)
                              .SingleOrDefault(c => c.Id == id);
            }
        }

        public static void AddCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Add(course);
                context.SaveChanges();
            }
        }

        public static void UpdateCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Attach(course);
                context.Entry(course).State = EntityState.Modified;
                context.SaveChanges();
            }
        }

        public static void DeleteCourse(int id)
        {
                using (Context context = GetContext())
                var stub = new stub() { Id = stubId };
                context.Entry(stub).State = EntityState.Deleted;

                context.SaveChanges();

        }
    }
}

3 Answers

Steven Parker
Steven Parker
216,108 Points

I spot a few issues:

  • no GetContext method has been defined
  • take a look at the other methods for examples of the using statement syntax
  • you forgot to enclose the code block after the using in braces
  • there's no "stub" type, your stub needs to be a new Course().
  • the passed-in argument is just "id" (not "stubId")
Steven Parker
Steven Parker
216,108 Points

You got off track a bit here:

                var course = context.Courses.Where(c => c.Id == id);

All you needed in your original was to change the object type from "Stub" to "Course", and use the passed-in argument:

                var stub = new Course() { Id = id };

change stub to course!

public static void DeleteCourse(int id) { using (var context = new Context() ) { var course = new Course() { Id = id }; context.Entry(course).State = EntityState.Deleted; context.SaveChanges(); } }

I now have this:

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
                              .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();
            }
        }

        public static Course GetCourse(int id)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Include(c => c.Teacher)
                              .SingleOrDefault(c => c.Id == id);
            }
        }

        public static void AddCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Add(course);
                context.SaveChanges();
            }
        }

        public static void UpdateCourse(Course course)
        {
            using (var context = new Context())
            {
                context.Courses.Attach(course);
                context.Entry(course).State = EntityState.Modified;
                context.SaveChanges();
            }
        }

        public static void DeleteCourse(int id)
        {
                using (var context = new Context() ){
                var course = context.Courses.Where(c => c.Id == id);
                context.Entry(course).State = EntityState.Deleted;

                context.SaveChanges();
}

        }
    }
}

am now getting this:

Bummer! Did you create a stub course entity using the passed in course 'id' parameter value and then pass it into the context 'Entry' method call?