.net qr code generator free Figure 4-17. Viewing the results of the postal code query in VB.NET

Encode QR Code in VB.NET Figure 4-17. Viewing the results of the postal code query

Figure 4-17. Viewing the results of the postal code query
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CHAPTER 4 s DATA BINDING WITH ASP.NET
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Using Parameters in Commands
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Now, this is all very well for a fixed SQL statement like the one we had hard-coded to query for postal code 98011. But what happens if you want the user to specify the postal code that they are searching for You achieve this using parameters. Thus, you can provide an application where the user specifies (using text input, request parameters, or other input mechanisms) what they want, and your application responds accordingly. Be careful when using parameters in SQL statements that are derived from user input, as this is a common source of SQL injection attacks. This type of hacker attack involves a cleverly crafted parameter value on the user s part and an insecure application that doesn t validate user input. This attack can allow a malicious user to access private data or even destroy your database. To use a parameter in SQL, you specify a placeholder for the parameter by prefixing it with the @ character. So, for example, our hard-coded query from earlier could be changed to this:
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sqlComm.CommandText = "SELECT AddressLine1 FROM Person.Address WHERE (PostalCode = @strZIP)";
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Then, before executing, you add the value of the parameter to the command, like this:
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sqlComm.Parameters.Add("@strZIP", strParamZIP);
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The value you ll assign to the parameterized postal code is contained in the variable strParamZIP. The value can be the result of text input, or, if you prefer, taken directly off the query string. The code to access it from the query string will look like this:
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string strParamZIP = "98011"; if (Request.Params["ZIP"] != null) strParamZIP = Request.Params["ZIP"];
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But if you use code like this, don t forget to sanitize strParamZIP before passing it to the database to avoid injection attacks. By sanitize, I mean that you should evaluate the value contained within strParamZIP and make sure it s a valid postal code, not some other (invalid) text. Now if you run your application, your query string can contain a postal code, and the query results for that postal code will be displayed. Figure 4-18 shows an example of this where I used a postal code of 14111.
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CHAPTER 4 s DATA BINDING WITH ASP.NET
Figure 4-18. Using a parameterized query
Data Binding with Server Controls
You ve seen in the previous sections how ASP.NET and ADO.NET can be used to connect to databases and manipulate the data therein through connections, commands, and readers. However, most modern applications require flexible, graphical access to the same data. As a developer, you aren t going to want to develop all of this complex data access and binding code from the ground up. ASP .NET provides controls that give you visual- and designer-based access to data through data binding, but all of them use a DataSource control to provide access to the underlying database. Because we are using SQL Server data in this example, the SQL Server specific DataSource control will be used. You aren t limited to using this control, because .NET provides several others, such as ObjectDataSource and XMLDataSource, but these go beyond the scope of this chapter. Still, the principles that you learn from the SqlDataSource control will apply across all data sources when data binding is taken into context.
CHAPTER 4 s DATA BINDING WITH ASP.NET
Using the SQLDataSource Control
When you are using Visual Studio or Visual Web Developer Express, open the Designer to edit any ASP .NET page. You will see a Data tab on the Toolbox. This tab contains the SqlDataSource control. Drag and drop it onto the design surface, and its Tasks pane will open (see Figure 4-19).
Figure 4-19. The SqlDataSource control
This pane contains a Configure Data Source link. Selecting this link will launch the SQL Server Connection wizard (see Figure 4-20). The first step in this wizard is to select a database connection, if one already exists.
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