Program.cs

using System;
using Microsoft.EntityFrameworkCore;
using System.Collections.Generic;
using System.Linq;

namespace ef_play
{
    class Program
    {
        public class Blog
        {
            public string Id { get; set; }
            public string Title { get; set; }

        }
        public class BloggingContext : DbContext
        {
            public DbSet<Blog> Blogs { get; set; }

            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                optionsBuilder.UseSqlite("Data Source=blogging.db");
            }

            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                modelBuilder.Entity<Blog>().HasAlternateKey(b => b.Title);
            }
        }

        static void Main(string[] args)
        {
            string blogId = null;

            using (var db = new BloggingContext()) {
                db.Database.EnsureCreated();
                var blog = new Blog {
                    Title = Guid.NewGuid().ToString()
                };
                db.Add(blog);
                db.SaveChanges();
                blogId = blog.Id;
                Console.WriteLine($"Printing blog title for the first time: {blog.Title}");
            }

            using (var db = new BloggingContext()) {
                var blog = new Blog {
                    Id = blogId,
                    Title = Guid.NewGuid().ToString()
                };
                db.Update(blog);
                db.SaveChanges();
                Console.WriteLine($"Printing blog title for the second time: {blog.Title}");
                Console.WriteLine($"Printing original values: {db.Entry(blog).OriginalValues["Title"]}");
            }
            
            using (var db = new BloggingContext()) {
                var blog = db.Blogs.FirstOrDefault(b => b.Id == blogId);
                Console.WriteLine($"Printing blog title for the third time: {blog.Title}");
            }
        }
    }
}