Pro CSharp And The .NET 2.0 Platform (2005) [eng]

824CHAPTER 22 ■ DATABASE ACCESS WITH ADO.NET

the wizard has created a new type deriving from DataSet named CarsDataSet. As you can see in Figure 22-24, this class type defines a number of members that allow you select, modify, and update its contents.

Figure 22-24. The strongly typed DataSet

Once the wizard completes its task, it places a member variable of type CarDataSet within your Form’s *.Designer.cs file (which is the same member variable manipulated in the Load event of your Form):

partial class MainForm

{

...

private CarsDataSet carsDataSet;

}

The Autogenerated Data Component

In addition to the strongly typed DataSet, the wizard generated a data component (named InventoryTableAdapter in this case) that encapsulates the underlying data connection, data adapter, and command objects used to interact with the Inventory table:

public partial class InventoryTableAdapter : System.ComponentModel.Component

{

// field data for data access.

private System.Data.SqlClient.SqlDataAdapter m_adapter; private System.Data.SqlClient.SqlConnection m_connection; private System.Data.SqlClient.SqlCommand[] m_commandCollection;

...

}

As well, this component defines custom Fill() and Update() methods that are tailor-made to operate on your CarsDataSet, in addition to a set of members used to insert, update, or delete row

data from the internal Inventory table. I’ll leave it up to interested readers to dive into the implementation details of each member. The good news is that after all your work in this chapter, the code behind each member should look quite familiar.

■Note If you are interested in taking a deeper look at the ADO.NET object model, including the numerous Visual Studio 2005 designers, check out Pro ADO.NET 2.0 by Sahil Malik (Apress, 2005).

Summary

ADO.NET is a new data access technology developed with the disconnected n-tier application firmly in mind. The System.Data namespace contains most of the core types you need to programmatically interact with rows, columns, tables, and views. As you have seen, the .NET platform ships with numerous data providers that allow you to leverage the connected and disconnected layers of ADO.NET.

Using connection objects, command objects, and data reader objects of the connected layer, you are able to select, update, insert, and delete records. As you have seen, command objects support an internal parameter collection, which can be used to add some type safety to your SQL queries and are quite helpful when triggering stored procedures.

The centerpiece of the disconnected layer is the DataSet. This type is an in-memory representation of any number of tables and any number of optional interrelationships, constraints, and expressions. The beauty of establishing relations on your local tables is that you are able to programmatically navigate between them while disconnected from the remote data store.

You also examined the role of the data adapter in this chapter. Using this type (and the related

SelectCommand, InsertCommand, UpdateCommand, and DeleteCommand properties), the adapter can resolve changes in the DataSet with the original data store. Also, you learned about the connected layer of ADO.NET and came to understand the role of data reader types.

P A R T 5

■ ■ ■

Web Applications and XML

Web Services

830 CHAPTER 23 ■ ASP. NET 2 . 0 WEB PAGES AND WEB CONTROLS

Figure 23-1. The HTTP request and response cycle

Another aspect of web development that is markedly different from traditional desktop programming is the fact that HTTP is an essentially stateless wire protocol. As soon as the web server emits a response to the client, everything about the previous interaction is forgotten. Therefore, as a web developer, it is up to you take specific steps to “remember” information (such as items in

a shopping cart) about the clients who are currently logged on to your site. As you will see in the next chapter, ASP.NET provides numerous ways to handle state, many of which are commonplace to any web platform (session variables, cookies, and application variables) as well as some new techniques (view state, control state, and the cache).

Understanding Web Applications and Web Servers

A web application can be understood as a collection of files (*.htm, *.asp, *.aspx, image files, etc.) and related components (such as a .NET code library) stored within a particular set of directories on a given web server. As shown in Chapter 24, web applications have a specific life cycle and provide numerous events (such as initial startup or final shutdown) that you can hook into.

A web server is a software product in charge of hosting your web applications, and it typically provides a number of related services such as integrated security, File Transfer Protocol (FTP) support, mail exchange services, and so forth. Internet Information Server (IIS) is Microsoft’s enterprise-level web server product, and as you would guess, it has intrinsic support for classic ASP as well as ASP.NET web applications.

When you build ASP.NET web applications, you will often need to interact with IIS. Be aware, however, that IIS is not automatically selected when you install the Windows Server 2003 or Windows XP Professional Edition (you can’t install IIS on the Home editions of Windows). Therefore, depending on the configuration of your development machine, you may be required to manually install IIS before proceeding through this chapter. To do so, simply access the Add/Remove Program applet from the Control Panel folder and select Add/Remove Windows Components.

■Note Ideally, your development machine will have IIS installed before you install the .NET Framework. If you install IIS after you install the .NET Framework, none of your ASP.NET web applications will execute correctly (you will simply get back a blank page). Luckily, you can reconfigure IIS to host .NET applications by running the aspnet_regiis.exe command-line tool (using the /i flag).

Assuming you have IIS properly installed on your workstation, you can interact with IIS from the Administrative Tools folder (located in the Control Panel folder). For the purposes of this chapter, you are concerned only with the Default Web Site node (see Figure 23-2).

832 CHAPTER 23 ■ ASP. NET 2 . 0 WEB PAGES AND WEB CONTROLS

The ASP.NET 2.0 Development Server

ASP.NET 2.0 ships with a lightweight web server named WebDev.WebServer.exe. This utility allows developers host an ASP.NET 2.0 web application outside the bounds of IIS. Using this tool, you can build and test your web pages from any directory on your machine (which is quite helpful for team development scenarios and for building ASP.NET 2.0 web programs on Windows XP Home Edition, which does not support IIS).

■Note WebDev.WebServer.exe cannot be used to test classic ASP web applications.

When building a website with Visual Studio 2005, you have the option of using WebDev.WebServer.exe to host your pages. However, you are also able to manually interact with this tool from a .NET command prompt. If you enter the following command:

WebDev.WebServer.exe -?

you will be presented with a message box that describes the valid command-line options. In a nutshell, you will need to specify an unused port (via the /port: option), the root directory of the web application (via the /path: option), and an optional virtual path using the /vpath: option (if you do not supply a /vpath: option, the default is simply /). Consider the following usage:

WebDev.WebServer.exe /port:12345 /path:"C:\CodeTests\CarsWebSite"

Once you have entered this command, you can launch your web browser of choice to request pages. Thus, if the CarsWebSite folder had a file named MyPage.aspx, you could enter the following URL:

http://localhost:12345/CarsWebSite/MyPage.aspx

Many of the examples in this chapter and the next will make use of WebDev.WebServer.exe via Visual Studio 2005. Be aware that this web server is not intended to host production-level web applications. It is purely intended for development and testing purposes.

■Note The Mono project (see Chapter 1) provides a free ASP.NET plug-in for the Apache web server. Check out http://www.mono-project.com/ASP.NET for details.

The Role of HTML

Once you have configured a directory to host your web application, you need to create the content itself. Recall that web application is simply the term given to the set of files that constitute the functionality of the site. To be sure, a vast number of these files will contain syntactic tokens defined by the Hypertext Markup Language (HTML). HTML is a standard markup language used to describe how literal text, images, external links, and various HTML-based GUI widgets are rendered by the client-side browser.

This particular aspect of web development is one of the major reasons why many programmers dislike building web-based programs. While it is true that modern IDEs (including Visual Studio 2005) and web development platforms (such as ASP.NET) generate much of the HTML automatically, you will do well to have a working knowledge of HTML as you work with ASP.NET. While this section will most certainly not cover all aspects of HTML (by any means), let’s check out some basics.

HTML Document Structure

An HTML file consists of a set of tags that describe the look and feel of a given web page. As you would expect, the basic structure of an HTML document tends to remain the same. For example, *.htm files (or, alternatively, *.html files) open and close with <html> and </html> tags, typically define a <body> section, and so forth. Keep in mind that HTML is not case sensitive. Therefore, in the eyes of the hosting browser, <HTML>, <html>, and <Html> are identical.

To illustrate some HTML basics, open Visual Studio 2005, insert an empty HTML file using the File New File menu selection, and save this file under your C:\CodeTests\CarsWebSite directory as default.htm. As you can see, the initial markup is uneventful:

<html>

<body>

</body>

</html>

The <html> and </html> tags are used to mark the beginning and end of your document. As you may guess, web browsers use these tags to understand where to begin applying the rendering formats specified in the body of the document. The <body> scope is where the vast majority of the actual content is defined. To spruce things up just a bit, define a title for your page as so:

<html>

<head>

<title>This Is the Cars Website</title> </head>

<body>

</body>

</html>

As you would guess, the <title> tags are used to specify the text string that should be placed in the title bar of the calling web browser.

HTML Form Development

The real action of an *.htm file occurs within the scope of the <form> elements. An HTML form is simply a named group of related UI elements used to gather user input, which is then transmitted to the web application via HTTP. Do not confuse an HTML form with the entire display area shown by a given browser. In reality, an HTML form is more of a logical grouping of widgets placed in the

<form> and </form> tag set:

<html>

<head>

<title>This Is the Cars Web Site</title> </head>

<body>

<form id="defaultPage" name="defaultPage">

<!-- Insert web content here ->

</form>

</body>

</html>

This form has been assigned the ID and name of “defaultPage”. Typically, the opening <form> tag supplies an action attribute that specifies the URL to which to submit the form data, as well as the method of transmitting that data itself (POST or GET). You will examine this aspect of the <form>