Support for ValueGeneration OnUpdate

[smitpatel]

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

namespace EFSampleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var blog = new Blog { Value = "A" };
            using (var db = new MyContext())
            {
                // Recreate database
                db.Database.EnsureDeleted();
                db.Database.EnsureCreated();

                // Seed database
                var entry = db.Add(blog);
                Console.WriteLine(entry.CurrentValues["Discriminator"]);

                db.SaveChanges();
            }

            using (var db = new MyContext())
            {
                blog.Value = "B";
                var entry = db.Update(blog);
                Console.WriteLine(entry.CurrentValues["Discriminator"]);
                db.SaveChanges();
            }

            Console.WriteLine("Program finished.");
        }
    }


    public class MyContext : DbContext
    {
        private static ILoggerFactory LoggerFactory => new LoggerFactory().AddConsole(LogLevel.Trace);

        // Declare DBSets
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<SpecialBlog> SpecialBlogs { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            // Select 1 provider
            optionsBuilder
                .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=_ModelApp;Trusted_Connection=True;Connect Timeout=5;ConnectRetryCount=0")
                //.UseSqlite("filename=_modelApp.db")
                //.UseInMemoryDatabase(databaseName: "_modelApp")
                .EnableSensitiveDataLogging()
                .UseLoggerFactory(LoggerFactory);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            // Configure model
        }
    }

    public class Blog
    {
        public int Id { get; set; }
        public string Value { get; set; }
    }

    public class SpecialBlog : Blog
    {
    }
}

The "Discriminator" property on entity entry is set to correct value when doing Add but when doing Update the value is null. For relational it works since update does not change values in database due to partial update. Though the value is required for CosmosDb provider since there are not partial updates.

[divega]

This seems important for Cosmos DB, stored procedures and general client generated values for update could potentially could help with optimistic "offline lock".

[divega]

For the time being we have a workaround this for Cosmos DB.

[AndriySvyryd]

Duplicate of #6999