Often, one knows that a database query will return at most a single object.
To get that object, the following code is needed:
List<Book> bookList = BookPeer.doSelect(criteria);
Book book = null;
if (bookList.size > 1)
throw new TooManyRowsException("...");
book = bookList.get(0);
There should be methods named doSelectSingleRecord(...) generated in the Peer class which contains teh above code.