Chapter 12. ADO Data Updates
Chapter 11 focused on retrieving data from the database and managing the complexity of related tables. All of the examples focused on displaying data. In many applications, however, you will also want to allow the user to update the data in the database.
There are two aspects to writing web applications that allow users to update data. The first aspect is providing the user with a user interface that facilitates modifying the data. The second is to provide the programmatic support for the update: how do you insert new records, or modify or delete existing records once you know what changes you want to make? This chapter focuses on this second aspect; how you write the code to update the data in the database. To simplify the examples, this chapter shows very little of the user interface. Many of the examples will use hard-coded changes; others will use a very crude and simple form for updating the data tables.
Updating data in a database is very simple if you only update a single table, but once you update related tables, things get complicated. This chapter will explore how transactions can be used to ensure the integrity of your data. In addition, if your program will be used by more than one user at a time, you will encounter issues with concurrency; is it possible for one user’s changes to overwrite the changes of another user. This chapter also explores how you manage concurrency issues, and shows some of the powerful support available in the class ...