1. 8 Chapter Eight Server-side Scripts

2. 8 Chapter Objectives Create dynamic Web pages that retrieve and display database data using Active Server Pages Process form inputs using Active Server Pages Create a Web application using client- and server-side scripts

3. 8 Chapter Objectives Learn how to share data values among different pages in a Web application Insert, update, and delete database records using Active Server Pages

4. 8 Server-side Scripts Server-side scripts –Scripts that are processed on the Web server –Used to create dynamic Web pages that retrieve and display database data and modify data records Active Server Pages –Microsoft-specific Web pages containing server- side scripting commands to process user inputs and create dynamic Web pages that display database data

5. 8 Server-side Scripts Figure 8-1: Web site architecture using a server-side script

6. 8 Active Server Pages Active Server Page (ASP) –Text file that has an.asp extension and contains server-side script commands that can perform a variety of tasks –Usually contains HTML commands for creating a formatted Web page Netscape has a server-side scripting technology called LiveWire that is similar to Active Server Pages

7. 8 Active Server Pages Since ASPs are processed on a Web server, ASP files must be stored and run from a folder on the Web server –They cannot be displayed from a folder on the user’s workstation using a file URL –Programmers often store program files in folders that are named “bin” or have the word “bin” as part of the folder name

8. 8 Active Server Pages Access privileges that are available in Personal Web Server (PWS) include: –Read, which only allows users to view HTML documents –Execute, which allows users to run Web pages that contain executable programs as well as scripts –Scripts, which allows users to run Web pages that contain scripts, but do not run Web pages that contain executable programs

9. 8 Active Server Pages When creating an ASP, it is good practice to: –First create a static HTML Web page template file that contains all of the HTML tags and formatted text that you want to have displayed on the formatted Web page that is generated by the ASP –Then, add the script code for the dynamic components and be certain that the page’s HTML formatting will be correct

10. 8 ASP Commands The main difference between ASP files and HTML document files is ASP files contain ASP script code lines along with HTML commands in the Web page body –Script commands like HTML commands, can span multiple lines

11. 8 ASP Commands The beginning and ending points of ASP script code lines are signaled by script delimiter tags –The opening script delimiter tag is an opening angle bracket and a percent sign (<%) –The closing script delimiter tag is a percent sign and a closing angle bracket (%>)

12. 8 Displaying Database Data in an ASP To create an ADO database connection object, you must create a server object –Memory area on the Web server that stores the variables and other information needed to process the ASP Every time the ASP is executed, a new server object must be created

13. 8 Displaying Database Data in an ASP In the code to open an ODBC connection –You must specify the name of the server object, and use the Open method to specify that the object is to be opened –Specify the database type and database location; for an Access database, the database location is the drive letter, folder, path, and database filename

14. 8 Displaying Database Data in an ASP Figure 8-5: Code to open an Access database connection object

15. 8 Displaying Database Data in an ASP When finished using a database connection object, close the database connection; this makes its resources available to other Web server processes

16. 8 Displaying Database Data in an ASP In a Web page with server-side scripts: –All of the server-side commands enclosed in script delimiter tags are removed by the Web server when the Web page is processed –Only the finished HTML commands are sent to the user’s browser for display

17. 8 Passing URL parameters to an ASP URL parameter –Parameter passed to a target ASP as part of the ASP’s URL –Each URL parameter consists of a name/value pair, which consists of: The name of parameter variable An equal sign (=) The current parameter value

18. 8 Passing URL parameters to an ASP Note the parameter list is separated from the ASP filename with a question mark (?) If there are multiple URL parameter name/value pairs, each pair is separated from the next by an ampersand (&) Often, the URL parameter variable value is a value that must be inserted within the hyperlink tag

19. 8 Retrieving Input Parameters into an ASP To retrieve the value of a variable that is passed as a URL parameter, use the Request object –An object within an ASP that stores information that is sent from a user’s browser to the Web server The Request object has a Querystring property, which contains the name of the variable whose value will be retrieved as a URL parameter

20. 8 Retrieving Input Parameters into an ASP It can be tricky to create SQL queries that use URL parameters - You must concatenate text strings, blank spaces, and variable values together so that the variable string is formatted correctly

21. 8 Retrieving Input Parameters into an ASP Whenever creating a SQL query in an ASP that requires concatenating variable values together so that the variable string is formatted correctly, it is good practice to: –Create a string variable –Then assign the text that constitutes the query to the string variable

22. 8 Debugging ASP Scripts The common errors of forgetting to save a modified ASP file, or displaying a cached version of a previous file, apply to ASPs as well as client-side scripts When calling an ASP from another Web page and passing URL parameter values, always confirm the parameter name/value pairs are passed correctly by viewing the URL of the hyperlink that calls the ASP

23. 8 Debugging ASP Scripts A common error in ASP scripts occurs when inadvertently omitting an opening or closing script delimiter tag Figure 8-16: Source code with omitted script delimiter tag

24. 8 Debugging ASP Scripts Figure 8-17: Error message resulting from omitted script delimiter tag

25. 8 Debugging ASP Scripts When looking for causes of errors, always look at the code lines immediately before the line reported in the error message If you cannot locate the error visually, the next step is to systematically locate the code line that is causing the error In an ASP, you can track script execution by adding debugging messages

26. 8 Sharing Data Values Among Multiple ASPs Web applications with multiple pages usually share data values One approach is to pass data values from one Web page to a second Web page as URL parameters A second way to share data values among ASPs is to use form parameters

27. 8 Sharing Data Values Among Multiple ASPs Form parameters –Similar to URL parameters in that they consist of name/value pairs, and each name/value pair is separated from the next parameter name/value pair by an ampersand (&) –More convenient to use than URL parameters for passing form input values from one Web page to another –A problem with passing parameters either as URL parameters or as form parameters is that it forces the pages to be viewed in a certain order to ensure that the correct parameters are always passed

28. 8 Recordset To determine if a recordset contains data records, use the recordset beginning-of-file (BOF) and end-of-file (EOF) properties Recordset pointer - indicates the position of the current record in the recordset that is available for processing

29. 8 Recordset The BOF recordset property is true when the recordset pointer is before the first recordset record The EOF property is true when the recordset pointer is beyond the last record in the recordset If the recordset does not contain any records, both the BOF and EOF properties are false, and the recordset pointer is pointing to a valid recordset record

30. 8 Creating Client-side Scripts in ASPs Preprocessing the ASP –Use client-side scripts within ASPs so that when the user clicks a button on an HTML form, the form runs a client-side script that is embedded within the HTML code on the ASP

31. 8 Currently Selected Button in an Option Button Group To find the value of the currently selected option button of an HTML form, use a client-side script to write script code that: –Searches all of the form fields –Locates the form elements if the option button is selected When a code finds an option button, it checks to see if the option button is selected

32. 8 Currently Selected Button in an Option Button Group In referencing properties of HTML form elements in a client-side script, the property attribute can reference the following values: –Length, which returns the total number of form elements –Name, which references the name of an individual form element –Checked, which determines if a form radio button is selected

33. 8 Inserting Database Records with Jet Recordset Commands To insert new data records using Jet recordset commands, you must create a Web server object that is a recordset The advantage of using Jet recordset commands is that when you insert a new record in a table where the primary key is an AutoNumber data type, you can then immediately retrieve the value of the system-generated primary key

34. 8 Inserting Database Records with Jet Recordset Commands Parameters used by the recordset Open method command: –Data source A text string –Connection name Name of the ADO connection used to connect to the database

35. 8 Inserting Database Records with Jet Recordset Commands Parameters used by the recordset Open method command (cont.): –Cursor type Numerical value that specifies how records in the recordset can be viewed By default, the cursor type value is the number 0, which specifies the cursor is forward-only When updating records in a recordset, set the cursor type value to 1, which specifies that the cursor is a keyset cursor

36. 8 Inserting Database Records with Jet Recordset Commands Parameters used by the recordset Open method command (cont.): –Lock type Specifies how the recordset records are locked When this value is set to the number 1, the recordset is read-only When the lock type value is set to 2, pessimistic locking is enabled When the lock type value is set to 3, optimistic locking is enabled

37. 8 Using SQL Commands to Insert and Modify Database Records Advantage of using SQL commands –Allows your Web application to be used with databases other than Access Disadvantage of using SQL commands –There is no easy way to insert a new record into an Access database table that uses the AutoNumber data type for the record’s primary key, and then immediately retrieve the value of the new primary key into an ASP variable for further processing

38. 8 Creating Cookies in Server-side Scripts When a Web server requests a browser to create a cookie, this message must be sent in a header message to the browser –This arrangement is required because the request to create a cookie must be the first command that the browser receives from the Web server when it sends a Web page to be displayed

39. 8 Creating Cookies in Server-side Scripts To send a header message instructing a browser to create a cookie name/value pair, the Web page output must be buffered –This means that as the ASP commands are executed, all of the output is stored on the Web server, and then is sent to the browser as a single unit after all of the script commands have been executed to the Web server

40. 8 Suppressing Form Parameter Values in URLs HTML forms have two primary methods for sending inputs to a Web server: –The default method, also called the GET method –The POST method

41. 8 Suppressing Form Parameter Values in URLs After receiving form inputs, a GET request is passed as an environment variable to the program processing the request –An environment variable is a variable that is stored on a workstation and is available to any program running on the workstation

42. 8 Suppressing Form Parameter Values in URLs Two problems with the GET method –Parameter values are displayed in the URL address –Environment variables typically are limited to 255 characters HTML forms in Web applications should use the POST method to hide form parameters

43. 8 Summary Server-side scripts are processed on the Web server and are used to create dynamic Web pages Microsoft’s technology for supporting server-side scripts is called Active Server Pages (ASPs) An ASP must be stored in a folder on the Web server

44. 8 Summary To pass data values from one ASP to another, you can pass a URL parameter When an HTML form is submitted to the Web server, the values for all of the form elements are passed as form parameters Data values can also be shared using cookies

45. 8 Summary You can preprocess and ASP using client-side script commands embedded within the HTML commands generated by the ASP by enclosing the client-side script commands in … tags in the ASP heading section To insert database records using an ASP, you can insert the records using Jet recordset commands or SQL commands

46. 8 Summary When a Web server requests a browser to create a cookie, this request message must be sent in a header message to the browser To suppress form parameter values from appearing as part of the URL displayed in the browser’s Address box, you can submit HTML forms using the POST method