Populating IEnumerable<class> with JSON result - json

Question

I previously had the following line of code from within my AdminController that was successfully returning a list of relevant subsections from within a course:
[AcceptVerbs(HttpVerbs.Get)]
public JsonResult GetCourseSections(int courseID)
{
var Sections = dbcontext.CourseSection.Where(cs => cs.CourseID.Equals(courseID)).Select(x => new
{
sectionID = x.CourseSectionID,
sectionTitle = x.Title
);
return Json(Sections, JsonRequestBehavior.AllowGet);
}
I was informed to take this out of the controller as it was bad practice to call dbcontext and so i moved this to the AdminViewModel. Within my AdminViewModel I have a variable public List CourseSectionList { get; set; } and I am trying to populate this variable with the JSON request details. My code is as follows:
AdminViewModel
public void GetCourseSectionDetails(int courseID)
{
var Sections = dbcontext.CourseSection.Where(cs => cs.CourseID.Equals(courseID)).Select(x => new CourseSection
{
CourseSectionID = x.CourseSectionID,
Title = x.Title
});
this.CourseSectionList = Sections.ToList();
}
AdminController
[AcceptVerbs(HttpVerbs.Get)]
public JsonResult GetCourseSections(int courseID)
{
avm.GetCourseSectionDetails(courseID);
var Sections = avm.CourseSectionList.Where(cs => cs.CourseID.Equals(courseID)).Select(x => new
{
sectionID = x.CourseSectionID,
sectionTitle = x.Title
});
System.Diagnostics.EventLog.WriteEntry("Application", "JSON=" + Sections.ToList(), System.Diagnostics.EventLogEntryType.Error);
return Json(Sections, JsonRequestBehavior.AllowGet);
}
I am getting the error The entity or complex type 'MetaLearning.Data.CourseSection' cannot be constructed in a LINQ to Entities query. How can I populate this.CourseSectionList variable using the Sections?

Answer 1

As pointed by your error message, you can't, in linq to entities, use a
.Select(m => new <Entity>{bla bla})
where <Entity>... is one of your model's entity.
So either you use a "non model" class (DTO), which has the properties you need, or you have to enumerate before selecting (because linq to objects has not that limitation)
.ToList()
.Select(m => new <Entity>{bla bla});
You can find some nice explanations of why it's not possible here
EDIT :
you may also do something like that, if you wanna retrive only some properties of your entity, and don't wanna use a DTO :
return ctx
.CourseSection
.Where(cs => cs.CourseID.Equals(courseID))
//use an anonymous object to retrieve only the wanted properties
.Select(x => new
{
c= x.CourseSectionID,
t= x.Title,
})
//enumerate, good bye linq2entities
.ToList()
//welcome to linq2objects
.Select(m => new CourseSection {
CourseSectionID = m.c,
Title = m.t,
})
.ToList();

Answer 2

You don't need to repeat the same code in the controller, but directly pass the list to the view.
This being said I am informing you that placing data access code in your view model is even worse practice than keeping it in the controller. I would recommend you having a specific DAL layer:
public interface IRepository
{
public IList<CourseSection> GetSections(int courseID);
}
which would be implemented:
public class RepositoryEF : IRepository
{
public IList<CourseSection> GetSections(int courseID)
{
using (ctx = new YourDbContextHere())
{
return ctx
.CourseSection
.Where(cs => cs.CourseID.Equals(courseID))
.Select(x => new CourseSection
{
CourseSectionID = x.CourseSectionID,
Title = x.Title,
})
.ToList();
}
}
}
and finally have your controller take the repository as dependency:
public class SomeController : Controller
{
private readonly IRepository repo;
public SomeController(IRepository repo)
{
this.repo = repo;
}
[AcceptVerbs(HttpVerbs.Get)]
public ActionResult GetCourseSections(int courseID)
{
var sections = this.repo.GetSections(courseID);
return Json(sections, JsonRequestBehavior.AllowGet);
}
}

Answer 3

I did this as follows using Darin's answer as a guide:
ViewModel
public void GetCourseSectionDetails(int courseID)
{
this.CourseSectionList = dbcontext.CourseSection.AsEnumerable().Where(cs => cs.CourseID.Equals(courseID)).Select(x => new CourseSection
{
CourseSectionID = x.CourseSectionID,
Title = x.Title
}).ToList();
}
Controller
[AcceptVerbs(HttpVerbs.Get)]
public JsonResult GetCourseSections(int courseID)
{
var sections = avm.CourseSectionList;
return Json(sections, JsonRequestBehavior.AllowGet);
}