make barcode with vb.net 19: Windows Presentation Foundation in C#

Paint Code 128 Code Set B in C# 19: Windows Presentation Foundation

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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.

Although one can certainly write an entire book on relational databases, and another on SQL, the essentials of these technologies aren t hard to understand, and you ll understand the chapter better if we spend a little time on the basics. A database is a repository of data. A relational database organizes your data into tables. In this chapter, we ll use the Northwind database, which is available as a free download from Microsoft. It was originally intended for a much older version of SQL Server, but it works well for our examples in this chapter without requiring too much installation work on your part.

The Northwind database is a database file that s intended for testing and practice purposes. To use the database, you ll need to make sure that you have SQL Server Express edition. If you re using Visual Studio, it was installed by default. If you re using C# Express, installing SQL Server was optional, and if you followed the instructions in 1, you already have it installed. If not, head back to 1 and check out the installation instructions there. If you re using Windows Vista, you re going to need to do a bit of extra work (if not, you can skip the next few paragraphs). Vista requires that only an administrator can install and access databases, but your default user isn t automatically added to the SQL Server Administrators group. Fortunately, there s an easy fix for this problem: 1. Go to C:\Program Files\Microsoft SQL Server\90\Shared (assuming you installed SQL Server to its default location). 2. Run the SqlProv.exe application. 3. You ll see the usual Windows Vista confirmation window. Click Confirm. 4. This starts the User Provisioning Tool, shown in Figure 20-1. In the User to provision box, make sure the computer name and the username of the user you want to grant permissions to are entered; they should be there automatically. The Available permissions box looks like it should have a long list, but there s really only one permission available, and it should be selected already. 5. Click the >> button to grant permission to that user, and then click OK to close the tool. Next, download the Northwind database from this location: http://www.microsoft.com/downloads/details.aspx FamilyID=06616212-035646A0-8DA2-EEBC53A68034 You ll download an .msi file, which you can then run to install the databases on your hard drive. By default, they install to c:\SQL Server 2000 Sample Databases.

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