using System;

    using System.Linq;

    using System.Collections;

    using System.Collections.Generic;

    public class Program

    {

        public class DbSet<T> : List<T>

        {

        }

        public class User

        {

            public string Name { get; set; }

            public override string ToString()

            {

                return "User " + Name;

            }

        }

        public class Transaction

        {

            public decimal Amount { get; set; }

            public override string ToString()

            {

                return "Transaction " + Amount.ToString("0.00");

            }

        }

        public class DatabaseContext

        {

            public DbSet<User> GetUsers() 

            {

                return new DbSet<User>()

                {

                    new User { Name = "Bob" },

                    new User { Name = "Alice" }

                };

            }

            public DbSet<Transaction> GetTransactions() 

            {

                return new DbSet<Transaction>()

                {

                    new Transaction { Amount = 12.34M },

                    new Transaction { Amount = 56.78M }

                };

            }

        }

        public class HelperClass

        {

            private readonly DatabaseContext _db;

            public HelperClass(DatabaseContext db)

            {

                _db = db;

            }

            public DbSet<T> GetDataSource<T>()

            {

                var targetType = typeof(DbSet<T>);

                return _db.GetType()

                    .GetMethods()

                    .Where( m => m.ReturnType == targetType)

                    .Single()

                    .Invoke(_db, null) as DbSet<T>;

            }

            public IEnumerable GetDataSource(Type type)

            {

                var targetType = typeof(DbSet<>).MakeGenericType(new Type[] { type});

                return _db

                    .GetType()

                    .GetMethods()

                    .Where( m => m.ReturnType == targetType)

                    .Single()

                    .Invoke(_db, null) as IEnumerable;

            }

        }

        public static void Main()

        {

            var helperClass = new HelperClass(new DatabaseContext());

            foreach (var u in helperClass.GetDataSource<User>())

            {

                Console.WriteLine(u);

            }

            foreach (var t in helperClass.GetDataSource(typeof(Transaction)))

            {

                Console.WriteLine(t);

            }

        }

    }