Concurrency using xmin

[flipchart]

I'm trying to use optimistic concurrency using xmin, but I'm not getting any exceptions thrown when the specified xmin value is "incorrect" (i.e. not what is in the DB).

See the gist here and note line 27

I've logged the SQL for the statement and it does contain an appropriate WHERE clause on the xmin value, however, I can't seem to log the parameter values, and I suspect that the loaded xmin value is being sent to the DB, rather than the value (1) that I specify.

Am I doing something wrong?

[flipchart]

Apologies! This is an EF issue (as seen with the other providers). It's due to loading the entity, rather than attaching a newly constructed one

[mikylebaksh]

I wanted to expand on this.

To anyone coming here in the future, the correct way to verify concurrency is to follow the answer here: https://stackoverflow.com/a/47480552

In other words, to correct the linked gist by @flipchart:

using System;
using Microsoft.EntityFrameworkCore;

namespace DataSetSerialization
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            var fooId = Guid.NewGuid();

            using (var context = new TestContext())
            {
                context.Add(new Person
                {
                    Id = fooId,
                    Name = "Foo",
                });

                context.SaveChanges();
            }

            using (var context = new TestContext())
            {
                var wes = context.Find<Person>(fooId);
                wes.Name = "Bar";

                context.Entry(wes).Property(x => x.XMin).OriginalValue = (uint) 1;

                // context.SaveChanges throws DbUpdateConcurrencyException
                context.SaveChanges();
            }
        }
    }

    internal class TestContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseNpgsql("User ID=postgres;Password=xxxx;Host=localhost;Port=5432;Database=test;Pooling=true;");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Person>(b =>
            {
                b.Property(x => x.XMin)
                    .HasColumnName("xmin")
                    .HasColumnType("xid")
                    .ValueGeneratedOnAddOrUpdate()
                    .IsConcurrencyToken();
            });

            base.OnModelCreating(modelBuilder);
        }
    }

    public class Person
    {
        public Guid Id { get; set; }
        public string Name { get; set; }

        public uint XMin { get; set; }
    }
}