public static void EnsureSeedDataForContext(this LibraryContext context) { if (context.Authors.Any()) { return; } //init seed data Publisher publisher = new Publisher() { Name = "Znak" }; var authors = new List <Author>() { new Author() { FirstName = "Donna", LastName = "Tartt", Books = new List <Book>() { new Book() { Title = "Szczygieł", ISBN = 9788324026524, Publisher = publisher }, new Book() { Title = "Tajemna Historia", ISBN = 9788324027415, Publisher = publisher }, new Book() { Title = "Mały Przyjaciel", ISBN = 9788324035571, Publisher = publisher } } }, new Author() { FirstName = "James", LastName = "Jones", Books = new List <Book>() { new Book() { Title = "From Here To Eternity", ISBN = 8497898745, Publisher = new Publisher() { Name = "Książnica" } } } } }; context.Authors.AddRange(authors); context.SaveChanges(); }