using Microsoft.EntityFrameworkCore;
using System;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static async Task Main()
        {
            var options = new DbContextOptionsBuilder();
            options.UseInMemoryDatabase("Widgets");

            using var db = new WidgetContext(options.Options);

            db.Set<Widget>().AddRange(
                new Widget { Name = "Foo" },
                new Widget { Name = "Bar" },
                new Widget { Name = "Fizz", Tag = "fizz" }
                );
            await db.SaveChangesAsync();

            var query = db.Set<Widget>().Where(w => w.Tag == "fizz");

            foreach (var w in await query.ToListAsync())
            {
                Console.WriteLine(w.Name);
            }
        }
    }

    public class Widget
    {
        public int Id { get; set; }

        [Required(AllowEmptyStrings = false)]
        public string Name { get; set; }

        internal string Tag { get; set; }
    }

    class WidgetContext : DbContext
    {
        public WidgetContext(DbContextOptions options)
            : base(options)
        {
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<Widget>();
        }
    }
}