Design Notes
Boxes like this in the Shopping Cart example have a discussion on the techniques used on each script page.  Please open the script source files if you want to follow the discussions in detail. Please see the box below for details of the plan for the whole Shopping Cart CD.

Try out this example by running ShopCart\Image\dyncd\DynCD.exe

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Dynamic-CD Example

Shopping Cart

Version 1.1, 07 August 2001
Design Notes, 25 June 2001.


This example shows Dynamic-CD in action, accessing a database and building up an order. The completed order is sent to the online PHD web site.

This "Shopping Cart" CD lets you order various parts from a catalog of Books, CDs and other Trivia. The order cart is saved between sessions in a database in your Windows temporary directory. Clicking on the "Go to Check Out" button transfers the order to the online PHD web site.

If you are running this example using the evaluation version of Dynamic-CD, you will only be able to run 10 scripts before Dynamic-CD quits. However if you restart Dynamic-CD, you will be able to continue with your order because the scripts have stored it in a database.


This client side image map appears on each page.  Clicking on "Books", "CDs" or "Trivia" displays a list of items in each category.  Clicking on "Cart" shows the user's cart of purchases.

This option simply lists all the available parts, organised by category.
Clicking on a More Info link will show the Full Description of a part.

This option displays the complete product list, with clickable links to add an item to the cart.

This option shows the cart, ie all items in the current order.  On the cart page you can change the quantity of each item required or remove items from the order.  Finally, you can proceed to the check out at the PHD web site.


Shopping Cart Design Notes

Introduction

This example shows how Dynamic-CD scripts and databases can be used to put a product catalog on a CD.  The scripts list all the available parts and show how to build up an order.  The Cart has an option to send the order to a Check Out at the PHD web site; when there, the CD prices are checked against the current prices and a revised order displayed; the order is not stored in a database.

The list of available parts is found from a Product database on the CD.  The cart of ordered items is stored in a database that is created in the user's Windows temporary directory.  Unless the user clears this directory, the cart persists from one session to the next.  A modified copy of the Product database is used online to display the latest prices for ordered items.

Site design

The site uses four scripts on the CD and one script on the PHD server.  A client side image map is used to provide quick links to the "Order Items" categories and the "Cart".

The CD scripts use three "include" files that define constants and common functions and subroutines.  These are described below.

The "List all available items" script (list.asp) and the "More information" script (moreinfo.asp) show how to do simple database accesses.

The guts of the CD site are in the "Order Items" script (pick.asp) and the "Cart" script (cart.asp).

The "Order Items" script either displays all products, or only products in the selected category.  For each listed product there is a link to let you add one more of the chosen item to your cart.
The script also lists the total number of items in your cart.

The "Cart" script does several jobs.  Its primary purpose is to display the contents of the current cart.  It also accepts order items from the "Order Items" script, lets you update the order quantities, and clear the cart.  Finally it also provides a means of transferring the order to the online web site.

The "Check Out" script on the PHD web site (CheckOut.asp) accepts the order from the CD "Cart" script.  It lists the order again, looking up the latest prices in the online product database.  Any price changes are indicated to the user.

Note that the site design suffers from the "Back problem", ie if the user presses the Back button in their browser then ordered items can seem to be removed from the order.  However most folk understand that systems can be fooled if you do this.

Parts Database on CD

The figure on the right shows the tables in the Parts database file ShopCart.mdb.  I created the structure in Access 2000 and added the example data by hand.  I then converted the database into Access 97 format just to be on the safe side.  You can open this database to look at the raw data.  I have only provided a Full Description for a few items in the Parts table.

The Categories table contains the list of categories, ie "Books", "CDs" and "Trivia".  The Categories table ID field is a unique "Autonumber" integer.  The Description field is the category name.  The Order field is used to sort the categories into the desired order when displaying choices to the user.

The Parts table contains the part definitions for all categories.  The Parts table ID field is a unique "Autonumber" integer.  The Category ID field links the Parts and Categories tables, so that the scripts can find all the parts that are of a certain category, and vice versa.  The PartNo field identifies the part, with the Description field giving a part name for display to the user.  The Full Description field has more information in HTML form.  Finally the Price field gives the part's cost in pounds sterling (GBP, ).

Finally, here's a useful tip for determining the SQL needed to query the database.  In Access, design a Query that suits your need.  Then copy the text from the SQL View to your script.

Parts Database online

The Parts database is also online in file ShopCart2.mdb.  The database structure is exactly the same, as is the data except that some prices have been changed up or down.

The "Check Out" script does not cope with situations where a part is no longer available.  If this might happen on your site, then make sure your online check out can cope.

Order Database on CD

The user's order is stored in an Order database called DynCart.mdb in their Windows temporary directory.  This database is created when it is first needed.  The figure on the right shows the one table called Order that is created in the database.  The Quantity and PartNo fields hopefully are obvious, with each record storing one order line. 

The "Cart" script maintains the values in this database.  Note that if the Quantity field goes down to zero, then the record is not deleted from the database.  Instead, the order line is simply not listed on screen.

Note that there is no option to delete this database; you could use the  FileSystemObject  to do this job.
The database will be removed if the user selects the "Disk Cleanup" option in Windows Explorer.

Directory structure

This example directories are structured as follows:
ShopCart--- Source
--- Image--- dyncd
The entire site is developed in ShopCart\Source, ie this directory contains all the static pages, images, the ASP scripts and the databases.  The file ShopCart\ShopCart.dcd is the Dynamic-CD-Wizard project file.  This tells Dynamic-CD-Wizard to build the CD image in the ShopCart\Image directory; building the CD image makes a dyncd directory in ShopCart\Image.  Note that port 8003 is specified in the Dynamic-CD-Wizard Advanced options; this lets this example run while the Dynamic-CD Documentation is being viewed.  The scripts are not encrypted in the CD image.

Try out this example by running ShopCart\Image\dyncd\DynCD.exe.  You can inspect the scripts in Notepad by clicking on the "view source" link in the Design Notes for each page.  Alternatively use your favourite editor to view or change the scripts in the ShopCart\Source directory.  Use Access 97 or later to view or change the databases.  If you make any changes, use Dynamic-CD-Wizard to rebuild the CD image and try it out.

Script structure

Each script starts off with a Server Side Include (SSI) of three files.  adovbs.inc (from Microsoft) contains most of the ADO constants that might be wanted.  vbsconst.inc contains additional VB constants.  Finally cartutil.asp contains several subroutines and functions that are used in all scripts - see below.

<!--#INCLUDE FILE="adovbs.inc"-->
<!--#INCLUDE FILE="vbsconst.inc"-->
<!--#INCLUDE FILE="cartutil.asp"-->

Make sure that the constants you want to use are actually listed in these headers.  If they are not then VBScript silently assumes that the values are zero, which is almost certainly not what you want.  Using "Option Explicit" does not seem to work.  Note that VBScript predefines some constants such as VbCrLf.

The scripts then have some static HTML at the top of the returned page.  The bulk of the rest of the page is then returned from the script, with Design Notes and </BODY></HTML> as static HTML at the end.

The main code in each script is in subroutine RunMyScript.  At the very end, the script calls RunMyScript to do the work of the script.

As far as possible, the scripts try to avoid presenting the user with obscure errors.  Some such as "Could not open database" are pretty unavoidable.

Finally note that the code sets all object variables to Nothing once their use has been finished.

Cart Utilities

The SSI include file cartutil.asp defines variables, constants, subroutines or functions that are used by most scripts.

Variable PartsDbCon is used for the connection to the Parts database.  OrderDbCon is used for the connection to the Order database.  Constant ExchangeRate is set to one; this could be modified in future to help cope with other currencies.

Subroutine ReportError is used to write out an error message if a script runs into serious problems.

Function FormatCurrencyUK converts a Dbl value into a string with the value formatted as a UK currency.

Function Connect2Parts opens the Parts database on the CD.  It obtains the CD directory path from the "ROOT_DIR" Dynamic-CD variable using  Request.ServerVariables 
DIM rootPath, DbPath
rootPath = Request.ServerVariables( "ROOT_DIR")
DbPath = rootPath & "\ShopCart.mdb"
Subroutine CloseParts closes the connection to the Parts database.

Function OpenOrder creates or opens the Order database in the current user's Windows temporary directory (obtained from the "WINDOWS_TEMP_DIR" Dynamic-CD variable).  OpenOrder first tries to open the database.  If this fails, it tries to create it using the ADOX object.  It creates an empty database then opens it as normal using ADO.  (If the open fails, delay and try again - see below.)  OpenOrder finally adds the required Order table - see below for more information.
Subroutine CloseOrder closes the connection to the Order database.

Localisation

This example is hard-wired to use United Kingdom currency, pounds sterling, even if the CD is run elsewhere.  Rather than use the standard  FormatCurrency  routine, our function FormatCurrencyUK is used.

Script tips

Don't use FileSystemObject

A script could use the Microsoft standard  FileSystemObject  object to do file system work, eg see if a file exists, delete a file, or create a text file.  However, Windows 95 and Windows NT 4 and earlier do not support  FileSystemObject .

If you want to see if a file exists, then use the Dynamic-CD specific function  Server.FileExists ; this returns Boolean True if a file exists.

The first cut of these scripts used the  FileSystemObject   FileExists  method to see if the database files were present before trying to open them.  However it was decided to remove this test because the open would fail anyway if the database file were not present.

Open/Close in each script

The Shopping Cart scripts open and close connections to the database files in each script.  An alternative approach would be to open the databases at the beginning of the session (using a session variable or code in a global.asa file).  When is the best time to close the database connections - we don't know.  The connections will be cleared when Dynamic-CD stops.  However it seems neatest to open and close the connections in each script.  The time delay will be negligible.

Creating tables in NT4

The OpenOrder function creates the Order database if need be.  It does this using the ADOX object to create an empty database.  ADOX can be used to add a new table to a database (using the ADOX.Table object).  However adding a table in ADOX does not work in Windows NT 4.

Therefore OpenOrder adds the table to the empty database in a different way.  It closes ADOX, opens the database in ADO and adds the table by executing a "CREATE TABLE" SQL command.

Creating tables in fast computers

As described earlier, the OpenOrder function creates the Order database if need be.  This is done by creating an empty database using the ADOX object and then adding the Order table.  This process runs into problems on some computers.  We think the problem occurs on fast computers.

After OpenOrder creates an empty database using ADOX, it closes the ADOX object.  The script immediately then tries to open the new database using ADO.  This sometimes fails on fast computers.  We think that ADOX has not properly closed the new database file.  If a small delay is put in, the retried open will now succeed.

Field Access

Note that there seems to be a bug in the ADO recordset object.  If you refer to a recordset field explicitly more than once, then the second and subsequent accesses return an empty value. 

For example, the second line here will produce no output:

Response.Write CategoryRS("Description")
Response.Write CategoryRS("Description")

Rewrite the code like this:

descr = CategoryRS("Description")
Response.Write descr
Response.Write descr

Forming SQL queries

SELECT queries must use square brackets around the table name, eg:
OrderSQL = "SELECT * FROM Order"		' Will not work
OrderSQL = "SELECT * FROM [Order]"		' Will work
Set OrderRS = OrderDbCon.Execute( OrderSQL)