// Entity Framework Classic

// Doc: https://entityframework-classic.net/query-deferred

​

// @nuget: Z.EntityFramework.Classic

​

using System;

using System.Linq;

using System.Data.Entity;

​

public class Program

{

    public static void Main()

    {

        GenerateData();

​

        using (var context = new EntityContext())

        {           

            // Not do Select

            var futurValue = context.Customers.DeferredAverage(x => x.Age).FutureValue();

            // SELECT AVG(Age) FROM Customers

            Console.WriteLine("Average Customer Age is : " +   futurValue.Value);           

        }

    }

    public static void GenerateData()

    {

        using (var context = new EntityContext())

        {

            context.Customers.Add(new Customer() { Name = "Customer_A", Description = "Description", Age = 20 });

            context.Customers.Add(new Customer() { Name = "Customer_B", Description = "Description", Age = 30 });           

            context.Customers.Add(new Customer() { Name = "Customer_C", Description = "Description", Age = 32 });

            context.SaveChanges();  

        }

    }

​

    public class EntityContext : DbContext

    {       

        public EntityContext() : base(FiddleHelper.GetConnectionStringSqlServer())

        {       

        }

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

    }

    public class Customer

    {

        public int CustomerID { get; set; }

        public string Name { get; set; }

        public string Description { get; set; }

        public int Age { get; set; }

    }

}