Chapter 6. Writing to Web Databases

Many web database systems aren’t only information resources for users but are also tools for storing new information. In our online winestore, users and administrators write data to the database in several situations. Users can purchase wines by creating an order, they can become members, they can manage a shopping cart, and the winestore administrator can manage the stock.

Writing data in web database applications requires different techniques than reading data. Issues of transactions and concurrency become important, and we introduce these issues and the principles of dealing with them in this chapter. The introduction is practical: we focus on the basic management techniques of locking and unlocking tables, and how to safely implement simple database writes in MySQL when there is more than one user simultaneously accessing a database. Most importantly, we identify when special approaches are required, and when these can be safely omitted from a web database application.

We begin by discussing a <form> designed to capture input for database writes. We also include more simple example scripts that illustrate more about PHP and its use in processing <form> input. We discuss some of the problems of <form> submission and validation further in the next chapter.

We also include in this chapter an example illustrating the reload problem, where variables and values are resubmitted when a web page in a browser is, for example, resized. This has practical ...

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