Task for simulating SQL db with linq

DbTask.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Sockets;

namespace DbTask
{
    interface IEntity
    {    
        long Id { get; }
    }

    interface IEntityFactory<out T> 
    {
        T Instance { get; }
    }

    class DataBaseException : Exception
    {
        public DataBaseException()
        {
        }

        public DataBaseException(string message) : base(message)
        {
        }
    }
    
    class DataBase
    {
        private readonly IDictionary<Type, object> _tables = new Dictionary<Type, object>();

        public string Name { get; }

        public DataBase(string name)
        {
            Name = name;
        }

        public void CreateTable<T>() where T : IEntity
        {
            Type tableType = typeof(T);

            if (_tables.ContainsKey(tableType))
                throw new DataBaseException($"Table already exists {tableType.Name}!");

            _tables[tableType] = new List<T>();
        }

        public void InsertInto<T>(IEntityFactory<T> values) where T : IEntity
        {
            Type tableType = typeof(T);

            if (!_tables.ContainsKey(tableType))
                throw new DataBaseException($"Unknown table {tableType.Name}!");

            ((List<T>) _tables[tableType]).Add(values.Instance);
        }

        public IEnumerable<T> Table<T>() where T : IEntity
        {
            Type tableType = typeof(T);
            
            if (!_tables.ContainsKey(tableType))
                throw new DataBaseException($"Unknown table {tableType.Name}!");

            return (IEnumerable<T>) _tables[tableType];
        }
    }

    class Shop : IEntity
    {
        public long Id { get; }
        public string Name { get; }

        public Shop(long id, string name)
        {
            Id = id;
            Name = name;
        }
    }

    class ShopFactory : IEntityFactory<Shop>
    {
        private static long _id = 0;

        private string _name;

        public ShopFactory(string name)
        {
            _name = name;
        }

        public Shop Instance => new Shop(_id++, _name);
    }

    class Good : IEntity
    {
        public long Id { get; }
        
        public string Name { get; }
        
        public long ShopId { get; }

        public Good(long id, string name, long shopId)
        {
            Id = id;
            Name = name;
            ShopId = shopId;
        }
    }

    class GoodFactory : IEntityFactory<Good>
    {
        private static long _id = 0;

        private string _name;

        private long _shopId;

        public GoodFactory(string name, long shopId)
        {
            _name = name;
            _shopId = shopId;
        }

        public Good Instance => new Good(_id++, _name, _shopId);
    }

    class Sale : IEntity
    {
        public long Id { get; }

        public Sale(long id)
        {
            Id = id;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            DataBase db = new DataBase("ShopDb");

            db.CreateTable<Good>();
            db.CreateTable<Shop>();
            
            // <Shop> for similarity with SQL
            db.InsertInto<Shop>(new ShopFactory("Auchan"));
            db.InsertInto<Shop>(new ShopFactory("Magnit"));
            
            db.InsertInto<Good>(new GoodFactory("Pepsi", 0));
            db.InsertInto(new GoodFactory("3 korochki", 0));
            db.InsertInto(new GoodFactory("Ohota", 1));
            db.InsertInto(new GoodFactory("Lays", 1));

            var auchanId = (from shop in db.Table<Shop>() where shop.Name == "Auchan" select shop.Id).First();
            
            var allAuchanGoods = from good in db.Table<Good>() where good.ShopId == auchanId select good.Name;

            foreach (var goodName in allAuchanGoods)
            {
                Console.WriteLine(goodName);
            }

            try
            {
                var sales = from sale in db.Table<Sale>() select sale;
                Console.WriteLine(sales.FirstOrDefault());
            }
            catch (DataBaseException ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}