By Kenneth S Miller

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Let's consider the following scenario. We accept some numeric value from a form and insert it into the database. To keep our example simple, assume that we want to update a book's year of publication. To achieve this, we can create a form that has two fields: A hidden field containing the book's ID, and a text field to enter the year. We will skip implementation details here, and see how using a poorly designed script to process this form could lead to errors and put the whole system at risk. The form processing script will examine two request variables: $_REQUEST['book'], which holds the book's ID and $_REQUEST['year'], which holds the year of publication.

In the next chapter, we will deal with a very important aspect of any database-driven application—error handling. We will also extend our example application by giving it the ability to add and edit books and authors, thus making it more realistic and useful. [ 46 ] Error Handling Now that we have built our first application that uses PDO, we will take a closer look at an important aspect of user-friendly web applications—error handling. Not only does it inform the user about an error condition, it also limits the damage if an error is not detected when it occurred.

If this type of an error occurs, then we trap it with exceptions and display a fatal error message. The developers must correct the situation at once. Now that we have learned a bit about possible sources of errors, let's examine how PDO handles errors. [ 50 ] Chapter 3 Types of Error Handling in PDO By default, PDO uses the silent error handling mode. This means that any error that arises when calling methods of the PDO or PDOStatement classes go unreported. With this mode, one would have to call PDO::errorInfo(), PDO::errorCode(), PDOStatement::errorInfo(), or PDOStatement::errorCode(), every time an error occurred to see if it really did occur.

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