Question

I am working in MVC3, C# and using Razor. I don’t work with MVC on a consistent basis so I am constantly having to relearn things… I want a view that displays a list of schools (from a specified state) with a nested list of the students (from that school) that have the middle name ‘Bob’.

Seems simple enough but so far I am not able to find a solution.

Ex: VIEW

Results for Maryland

My First School:
– Billy Bob Johnson
– Sally Bob Simpson
– Adam Bob Jones

Another School:
– Arnold Bob Smith
– Cathy Bob Powers
– Jenny Bob Smith

The Other School:
– Barney Bob Edson
– Sue Bob Purdee
– Alan Bob Warfield

public class School
{ 
   public int SchoolId {get; set;} 
   public string Schoolname {get; set;} 
   public int StateId {get; set;} 
} 


public class Student
{ 
   public int StudentId {get; set;}
   public int SchoolId {get; set;} 
   public string Firstname {get; set;} 
   public string Middlename {get; set;} 
   public string Lastname {get; set;} 
} 


public class SchoolViewModel
{ 
   public int SchoolId {get; set;}
   public string Schoolname {get; set;}  
   public IEnumerable<Student> Bobs { get; set; }
} 

Getting a list by doing a SELECT with JOINS will give me a data set that needs additional work in order to display in the VIEW as illustrated above. I am thinking that there is a way to grab the nested list of students in a way that allows the data set to act like a mulitidimensional array. But I am not finding examples of that approach – leading me to think that THAT is not the way… ?? How do I grab the data in a way that makes the best use LINQ / MVC / ViewModel etc… ? 🙂

I was trying something like this – but don’t know if this is the right direction or not – and it gave me an error when I tried to set the Bobs. 🙂

I get an error like:
LINQ to Entities does not recognize the method ‘System.Linq.IQueryable`1[stuff] GetBobs(stuff)’ method, and this method cannot be translated into a store expression.

  private IQueryable<SchoolViewModel> GetSchools(int StateId)
  {
        var query = from s in db.Schools
                    where s.State == StateId
                    orderby s.Schoolname
                    select new SchoolViewModel
                    {
            SchoolId = s.SchoolId,
                        Name = s.Name,
                        Bobs = GetBobs(s.SchoolId)
                    };
    var results = query;
        return results;
    }

    private IQueryable<Student> GetBobs(int id)
    {

        var query = from s in db.Students
                    where s.Middlename == 'Bob'
                    where s.SchoolId == id
                    select s;

        var results = query;
        return results;
    }

Answer 1

Well you can always do this for the query portion, I’m guessing that’s where you are getting tripped up:

var schools = db.Schools
     .Where(x => x.State == "<Whatever>")
     .Select(x => new {
          School = x,
          Bobs = x.Where(y => y.MiddleName == "Bob")
     }).ToList();

List<Schools> schoolsView = new List<Schools>();
foreach(var x in schools)
{
     schoolsView.Add(new SchoolsViewModel(){
          //Set Properties here
          SchooldID = x.School.ID,
          SchoolName = x.School.Name,
          Students = x.Bobs.ToList() //You can project here if needed.
     };
}

return schoolsView;

Then for your view you can do this any number of ways but if you have the concrete ViewModel with the fixed output it’s just nested loops:

<ul>
@foreach(var m in Model)  //Assuming your model is a list of SchoolViewModels
{
     <li>@m.SchoolName
          <ul>
               @foreach(var s in m.Students)
               {
                    <li>@s.Name</li>
               }
          </ul>
     </li>
}
</ul>

You also have cute options for doing things like String.Join(",", Model.Students) to output the list but this is up to you.

Edit: Additional Clarification

You will also want to change your models a tad, I’m not sure what EF version you are using but in EF4.1+ you can specify your navigation properties to remove the need for an explicit join condition (which is the right approach in the end).

http://msdn.microsoft.com/en-us/library/bb738520.aspx

So your Schools model would become:

public class School
{ 
   public int SchoolId {get; set;} 
   public string Schoolname {get; set;} 
   public int StateId {get; set;} 
   public virtual IList<Student> Students {get; set; }
} 

And then in your DB configuration (If you are using fluent the configuration would be:

modelBuilder.Entity<School>()
     .HasMany(x => x.Students).WithRequired();

Then you gain the power of doing

db.Schools
    .Where(x => x.Name.Contains("Some Value"))
    .Include(x => x.Schools.Where(x => x.MiddleName.Contains("SomeValue")))
    .ToList();

Which even makes my prior query even more simple without needing to use ambiguous type definitions.

Hopefully this clarification helps a bit further.