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 db = new LabDb(options))
{
    await db.Database.EnsureCreatedAsync(); db.Blogs.Add(new Blog { Name = "A", Posts = { new Post { Title = "First" } } }); await db.SaveChangesAsync();
    var row = await db.Posts.Include(p => p.Blog).SingleAsync(); Check(row.BlogId > 0 && row.Blog.Name == "A", "saved FK graph"); Console.WriteLine("related:" + row.Blog.Name);
}
bool rejected = false;
await using (var invalid = new LabDb(options))
{
    invalid.Posts.Add(new Post { Title = "Orphan", BlogId = 9999 });
    try { await invalid.SaveChangesAsync(); }
    catch (DbUpdateException ex) when (ex.InnerException is SqliteException { SqliteErrorCode: 19, SqliteExtendedErrorCode: 787 }) { rejected = true; }
}
await using (var verify = new LabDb(options)) Check(rejected && await verify.Posts.CountAsync() == 1, "foreign key rejected without orphan");
Console.WriteLine("foreign-key:rejected");

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