DatabaseDriven Web Sites Morrison

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Database-Driven Web Sites
-Morrison Morrison

• Server-Side Scripts

Gayla M. Badillo
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Chapter Overview

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

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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

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

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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
  users 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

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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

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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 pages HTML
  formatting will be correct

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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

• 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 (lt)
• The closing script delimiter tag is a percent
  sign and a closing angle bracket (gt)

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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

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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

Figure 8-5 Code to open an Access database
connection object
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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
• In a Web page with server-side scripts
• All of the server-side commands enclosed in ltgt
  script delimiter tags are removed by the Web
  server when the Web page is processed
• Only the finished HTML commands are sent to the
  users browser for display

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Passing URL parameters to an ASP

• URL parameter
• Parameter passed to a target ASP as part of the
  ASPs 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

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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

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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 users 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

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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

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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

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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

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

• 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

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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

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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 records primary key, and then
  immediately retrieve the value of the new primary
  key into an ASP variable for further processing

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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

• 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

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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
• 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

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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

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Summary

• Server-side scripts are processed on the Web
  server and are used to create dynamic Web pages
• Microsofts technology for supporting server-side
  scripts is called Active Server Pages (ASPs)
• An ASP must be stored in a folder on the Web
  server
• 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

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Summary

• You can preprocess an ASP using client-side
  script commands embedded within the HTML commands
  generated by the ASP by enclosing the client-side
  script commands in ltSCRIPTgtlt/SCRIPTgttags in the
  ASP heading section
• To insert database records using an ASP, you can
  insert the records using Jet recordset commands
  or SQL commands
• 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 browsers
  Address box, you can submit HTML forms using the
  POST method