protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
EntityTypeBuilder<Book> bookBuilder = modelBuilder.Entity<Book>();
bookBuilder.HasMany(b => b.Chapters).WithOne(c => c.Book).HasForeignKey(c => c.BookId);
bookBuilder.Property<string>(b => b.Title).HasMaxLength(120).IsRequired();
bookBuilder.Property<string>(b => b.Isbn).HasMaxLength(20).IsRequired(false);
EntityTypeBuilder<Chapter> chapterBuilder = modelBuilder.Entity<Chapter>();
chapterBuilder.Property<string>(c => c.Title).HasMaxLength(120);
}
}