Most of the applications that you’ve written so far in this book have been short-lived things. They do their thing and end, and any information they need is either hardcoded or supplied by the user. That’s to be expected when you’re learning a language, but in the real world, many applications deal with large quantities of data, derived from somewhere else. That data could be in a database, or a text document, or an XML file, or one of tons of other storage methods. Dealing with data is another complex topic that can fill whole books on its own, but we’re going to give you a taste of it in this chapter and the next, starting with the traditional ADO.NET, and then introducing you to the brand-new Language Integrated Query (LINQ).

ADO.NET was designed to provide a disconnected data architecture, though it does have a connected alternative. In a disconnected architecture, data is retrieved from a database and cached (stored) on your local machine. You manipulate the data on your local computer and connect to the database only when you wish to alter records or acquire new data.

There are significant advantages to disconnecting your data architecture from your database. The biggest advantage is that your application, whether running on the Web or on a local machine, will create a reduced burden on the database server, which may help your application to scale well; that is, it doesn’t impose a substantially greater burden as the number of users increases. Database connections are resource-intensive, and it is difficult to have thousands (or hundreds of thousands) of simultaneous continuous connections. A disconnected architecture is resource-frugal, though there are times that all you want to do is connect to the database, suck out a stream of data, and disconnect; and ADO.NET has a Reader class that allows for that as well.

ADO.NET typically connects to the database to retrieve data, and connects again to update data when you’ve made changes. Most applications spend most of their time simply reading through data and displaying it; ADO.NET provides a disconnected subset of the data for your use while reading and displaying, but it is up to you as the developer to keep in mind that the data in the database may change while you are disconnected, and to plan accordingly.