Demonstrates efficiently querying the default MVC 5 entity framework model for users in a given role.

DemoGettingUsersInSpecificRole.cs

using System;
using System.Collections.Generic;
using System.Linq;
using WebApplication9.Models;

namespace WebApplication9
{
    public class DemoGettingUsersInSpecificRole
    {
        private readonly ApplicationDbContext _db;

        public DemoGettingUsersInSpecificRole(ApplicationDbContext dbContext)
        {
            if (dbContext == null) throw new ArgumentNullException("dbContext");
            _db = dbContext;
        }

        public IList<ApplicationUser> GetUsersInRole(string roleName)
        {
            var query =
                from r in _db.Roles
                where r.Name == roleName
                from ur in r.Users
                join u in _db.Users on ur.UserId equals u.Id
                select u;

            var users = query.ToList();
            return users;
        }
    }
}