using System;
using System.Linq;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Data.Sqlite;
using Microsoft.EntityFrameworkCore;

await using var connection = new SqliteConnection("Data Source=:memory:;Foreign Keys=True");
await connection.OpenAsync();
var options = new DbContextOptionsBuilder<LabDb>().UseSqlite(connection).Options;
await using (var seed = new LabDb(options)) { await seed.Database.EnsureCreatedAsync(); seed.Items.Add(new Item { Name = "Initial", Version = 1 }); await seed.SaveChangesAsync(); }
await using var first = new LabDb(options); await using var second = new LabDb(options);
var winner = await first.Items.SingleAsync(); var stale = await second.Items.SingleAsync();
winner.Name = "Winner"; winner.Version++; await first.SaveChangesAsync();
stale.Name = "Stale"; stale.Version++; bool conflict = false;
try { await second.SaveChangesAsync(); } catch (DbUpdateConcurrencyException ex) { conflict = ex.Entries.Count == 1; }
await using var verify = new LabDb(options); var stored = await verify.Items.AsNoTracking().SingleAsync();
Check(conflict && stored.Name == "Winner" && stored.Version == 2, "original token prevents stale write"); Console.WriteLine("conflict:detected"); Console.WriteLine(stored.Name + ":v" + stored.Version);

static void Check(bool condition, string name) { if (!condition) throw new InvalidOperationException("CHECK: " + name); }