ASP.NET 4 in VB 2010 : ADO.NET Fundamentals (part 1) - Understanding Databases, Configuring Your Database

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1. Understanding Databases

Almost every piece of software ever written works with data. In fact, a typical web application is often just a thin user interface shell on top of sophisticated data-driven code that reads and writes information from a database. Often, website users aren't aware (or don't care) that the displayed information originates from a database. They just want to be able to search your product catalog, place an order, or check their payment records.

The most common way to manage data is to use a database. Database technology is particularly useful for business software, which typically requires sets of related information. For example, a typical database for a sales program consists of a list of customers, a list of products, and a list of sales that draws on information from the other two tables. This type of information is best described using a relational model, which is the philosophy that underlies all modern database products, including SQL Server, Oracle, and even Microsoft Access.

As you probably know, a relational model breaks information down to its smallest and most concise units. For example, a sales record doesn't store all the information about the products that were sold. Instead, it stores just a product ID that refers to a full record in a product table, as shown in Figure 1.

Figure 1. Basic table relationships

Although it's technically possible to organize data into tables and store it on the hard drive in one or more files (perhaps using a standard like XML), this approach wouldn't be very flexible. Instead, a web application needs a full relational database management system (RDBMS), such as SQL Server. The RDBMS handles the data infrastructure, ensuring optimum performance and reliability. For example, the RDBMS takes the responsibility of providing data to multiple users simultaneously, disallowing invalid data, and committing groups of actions at once using transactions.

In most ASP.NET applications, you'll need to use a database for some tasks. Here are some basic examples of data at work in a web application:

  • E-commerce sites (like Amazon) use detailed databases to store product catalogs. They also track orders, customers, shipment records, and inventory information in a huge arrangement of related tables.

  • Search engines (like Google) use databases to store indexes of page URLs, links, and keywords.

  • Knowledge bases (like Microsoft Support) use less structured databases that store vast quantities of information or links to various documents and resources.

  • Media sites (like The New York Times) store their articles in databases.

2. Configuring Your Database

Before you can run any data access code, you need a database server to take your command. Although there are dozens of good options, all of which work equally well with ADO.NET (and require essentially the same code), a significant majority of ASP.NET applications use Microsoft SQL Server.

2.1. SQL Server Express

If you don't have a test database server handy, you may want to use SQL Server 2005 Express Edition, the free data engine included with some versions of Visual Studio and downloadable separately.

SQL Server Express is a scaled-down version of SQL Server that's free to distribute. SQL Server Express has certain limitations—for example, it can use only one CPU and a maximum of 1GB of RAM, and databases can't be larger than 10GB. However, it's still remarkably powerful and suitable for many midscale websites. Even better, you can easily upgrade from SQL Server Express to a paid version of SQL Server if you need more features later.

2.2. Browsing and Modifying Databases in Visual Studio

As an ASP.NET developer, you may have the responsibility of creating the database required for a web application. Alternatively, it may already exist, or it may be the responsibility of a dedicated database administrator. If you're using a full version of SQL Server, you'll probably use a graphical tool such as SQL Server Management Studio to create and manage your databases.

If you don't have a suitable tool for managing your database, or you don't want to leave the comfort of Visual Studio, you can perform many of the same tasks using Visual Studio's Server Explorer window. (Confusingly enough, the Server Explorer window is called the Database Explorer window in Visual Studio Web Developer Express.)

You may see a tab for the Server Explorer on the right side of the Visual Studio window, grouped with the Toolbox and collapsed. If you do, click the tab to expand it. If not, choose View => Server Explorer to show it (or View => Database Explorer in Visual Studio Web Developer Express).

Using the Data Connections node in the Server Explorer, you can connect to existing databases or create new ones. Assuming you've installed the pubs database (see the readme.txt file for instructions), you can create a connection to it by following these steps:

  1. Right-click the Data Connections node, and choose Add Connection. If the Choose Data Source window appears, select Microsoft SQL Server and then click Continue.

  2. If you're using a full version of SQL Server, enter localhost as your server name. This indicates the database server is the default instance on the local computer. (Replace this with the name of a remote computer if needed.) If you're using SQL Server Express, you'll need to use the server name localhost\SQLEXPRESS instead, as shown in Figure 2. The SQLEXPRESS part indicates that you're connecting to a named instance of SQL Server. By default, this is the way that SQL Server Express configures itself when you first install it.

    Figure 2. Creating a connection in Visual Studio
  3. Click Test Connection to verify that this is the location of your database. If you haven't installed a database product yet, this step will fail. Otherwise, you'll know that your database server is installed and running.

  4. In the Select or Enter a Database Name list, choose the pubs database. (In order for this to work, the pubs database must already be installed. You can install it using the database script that's included with the sample code, as explained in the following section.) If you want to see more than one database in Visual Studio, you'll need to add more than one data connection.

    Alternatively, you can choose to create a new database by right-clicking the Data Connections node and choosing Create New SQL Server Database.

  5. Click OK. The database connection will appear in the Server Explorer window. You can now explore its groups to see and edit tables, stored procedures, and more. For example, if you right-click a table and choose Show Table Data, you'll see a grid of records that you can browse and edit, as shown in Figure 3.

Figure 3. Editing table data in Visual Studio

The Server Explorer window is particularly handy if you're using SQL Server Express, which gives you the ability to place databases directly in the App_Data folder of your web application (instead of placing all your databases in a separate, dedicated location). If Visual Studio finds a database in the App_Data folder, it automatically adds a connection for it to the Data Connections group.

2.3. The sqlcmd Command-Line Tool

SQL Server includes a handy command-line tool named sqlcmd.exe that you can use to perform database tasks from a Windows command prompt. Compared to a management tool like SQL Server Management Studio, sqlcmd doesn't offer many frills. It's just a quick-and-dirty way to perform a database task. Often, sqlcmd is used in a batch file—for example, to create database tables as part of an automated setup process.

The sqlcmd tool is found in a directory like c:\Program Files\Microsoft SQL Server\100\Tools\Binn. The easiest way to run sqlcmd is to launch the Visual Studio command prompt (open the Start menu and choose All Programs => Microsoft Visual Studio 2010 => Visual Studio Tools => Visual Studio Command Prompt). This opens a command window that has the SQL Server directory set in the path variable. As a result, you can use sqlcmd anywhere you want, without typing its full directory path.

When running sqlcmd, it's up to you to supply the right parameters. To see all the possible parameters, type this command:

sqlcmd -?

Two commonly used sqlcmd parameters are –S (which specifies the location of your database server) and –i (which supplies a script file with SQL commands that you want to run). For example, the downloadable code samples include a file named InstPubs.sql that contains the commands you need to create the pubs database and fill it with sample data. If you're using SQL Server Express, you can run the InstPubs.sql script using this command:

sqlcmd -S localhost\SQLEXPRESS -i InstPubs.sql

If you're using a full version of SQL Server on the local computer, you don't need to supply the server name at all:

sqlcmd -i InstPubs.sql

And if your database is on another computer, you need to supply that computer's name with the –S parameter (or just run sqlcmd on that computer).


The parameters you use with sqlcmd are case sensitive. For example, if you use –s instead of –S, you'll receive an obscure error message informing you that sqlcmd couldn't log in.

Figure 4 shows the feedback you'll get when you run InstPubs.sql with sqlcmd.

Figure 4. Running a SQL script with sqlcmd.exe

You'll occasionally see instructions about using sqlcmd to perform some sort of database configuration. However, you can usually achieve the same result (with a bit more clicking) using the graphical interface in a tool like SQL Server Management Studio. For example, to install a database by running a SQL script, you simply need to start SQL Server Management Studio, open the SQL file (using the File => Open => File command), and then run it (using the Query => Execute command).

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