// @nuget: EntityFramework

using System;

using System.Linq;

using System.Data.Entity;

using System.Collections;

using System.Collections.Generic;

using System.ComponentModel.DataAnnotations;

using System.ComponentModel.DataAnnotations.Schema;

​

public class Program

{

    public static void Main()

    {

        using (var ctx = new SchoolContext())

        {

            var g1 = new Grade() {GradeName = "g1"};

            var g2 = new Grade() {GradeName = "g2"};

            ctx.Grades.Add(g1);

            ctx.Grades.Add(g2);

            var stud = new Student() {StudentName = "Bill", Grade = g1};

            ctx.Students.Add(stud);

            ctx.SaveChanges();

            var query =

                from g in ctx.Grades

                select new

                {

                       Name = g.GradeName, 

                       StuCount = g.Students.Count()

                };

            // The following displays Grades Student count - dotnetfiddle.net specific code

            FiddleHelper.WriteTable(query.ToList());

        }

    }

}

​

public class SchoolContext : DbContext

{

    public SchoolContext(): base(FiddleHelper.GetConnectionStringSqlServer()) // passed dotnetfiddle specific connction string

    {

    }

​

    public DbSet<Student> Students {    get;    set;}

​

    public DbSet<Grade> Grades {    get;    set;}

    public DbSet<Customer> Customers {get;set;}

    public DbSet<Order> Orders {get;set;}

}

​

​

public class Customer

{

    [Key]

    public int Id { get; set; }

    public string FullName { get; set; }

    public virtual System.Data.Entity.DbSet<Order> Orders  { get; set; }

}

public class Order

{

    [Key]

    public int Id { get; set; }

    public int CustomerId { get; set; }

    public string Title { get; set; }

    [ForeignKey("CustomerId")]

    public virtual  Customer Customer { get; set; }

}

​

​

​

​

​

​

​

​

​

public class Student

{

    public int StudentID {get;  set;}

    public string StudentName { get;    set;    }

    public Grade Grade{ get;    set;}

}

​

public class Grade

{

    public int GradeId {    get;    set;}

    public string GradeName {   get;    set;}

    public ICollection<Student> Students {  get;    set;}

}