public async Task <Book> TrySetAvailableAsync(string id)
{
var book = await BookStorage.ReadByIdAsync(id);
if (book.IsAvailable)
{
throw new InvalidOperationException("that book is already available.");
}
book.IsAvailable = true;
await BookStorage.UpdateAsync(book);
return(book);
}
public async Task <Book> GetBookByIdAsync(string id)
{
return(await BookStorage.ReadByIdAsync(id));
}