As we have discussed earlier, we want to extend our application so that we can add and edit books and authors. Also, our system should be able to protect us from entering the same book twice—by enforcing the unique index on the ISBN
column in the books table.
Before we proceed with the code, we will create the index. Fire up your command line client and enter the following command (which is the same for MySQL and SQLite):
CREATE UNIQUE INDEX idx_isbn ON books(isbn);
We will also make our edit book page serve two purposes at once—adding a new book and editing an existing one. The script will distinguish which action to take by the presence of the book ID, either in an URL or in a hidden form field. We will link to this new page from within books.php
, so that we will be able to edit every book just by clicking on a link on the books listing page.
This page is more complicated than those described in the previous chapter, so I will provide you with the code first and...