Beginning Web Development, Silverlight, and ASP.NET AJAX

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CHAPTER 11 ■ AJAX APPLICATIONS AND EMPOWERING THE WEB USER EXPERIENCE
This simply checks to see if the parameter is present. If it is, it loads its value into the
integer picID; otherwise it defaults it to 100.
Next, you set up your data connection and initialize a SQL query to use this
parameter:
string connectionString =
WebConfigurationManager.ConnectionStrings["AdventureWorksConnectionString"]
.ConnectionString;
SqlConnection con = new SqlConnection(connectionString);
string sql = "Select * from Production.ProductPhoto where ProductPhotoID=@ID";
SqlCommand cmd = new SqlCommand(sql, con);
cmd.Parameters.Add("@ID", picID);
This code pulls the connection string from the Web.Config file for the web application.
If you don’t have one already, refer back to Chapter 4 for instructions on installing
and configuring the database on your web site.
It then creates a new instance of a SqlConnection object, initializing it with this connection
string.
The SQL is simply a string, and in SQL strings you can specify parameters using the
@ directive, so it knows that when you say ProductPhotoID=@ID, it will be expecting a
parameter.
Next, a new SqlCommand is created using this SQL code on the configured connection.
Finally, the parameter is added to the command. SQLCommand objects have a collection of
parameters that is empty by default. When you add parameters to this collection, you
specify the parameter name (@ID in this case) and the parameter value (picID in this case).
When the command is executed, the SQL is assembled with the parameter values filling
in the placeholders.
The next step is to open the database and execute the SQL. When you execute a command,
a SqlDataReader object is returned, allowing you to read the results line by line.
This query will at most return one line (as there is only one picture per ProductPhotoId).
con.Open();
SqlDataReader sqlRead = cmd.ExecuteReader();
To access the contents of the SqlDataReader, the Read function is called. This reads a
single record at a time. As we have at most one record, we call this once. Calling this function
loads the next record, and returns true if it succeeds (i.e., if there is a next record),
and false if it doesn’t.
Thus, in this case, we can gate the sqlRead.Read, and in the true clause handle the
loading and writing of the image to the response. In the false clause, we can provide an
error message. Here’s the code: