Page 5 of 22 - Chapter 14

Some Standard Include Files

Web page and scripting creation do not easily lend themselves to code reuse. However, one way of accomplishing code reuse is server-side include files whereby a file is included within a page by use of the <!--#include file=""--> directive available with NT Server via ASP.

The next piece of scripting we will write is an include file to create a dynamic list of music categories available for browsing. Taking the information from the Category table in the database, this include file creates a table of links which when clicked takes the user to a list of goods available within that category.

Using the server-side include directive we will incorporate this file in a number of pages in the web site demonstrating code reuse.

The CategoryList Include File

The first thing our ASP code does is create an ADODB Recordset to obtain a list of categories from the database. We use the ASP Server object's CreateObject method to create a new ADODB.Recordset object. The Recordset's Open method fetches the data we need by executing the ListCategories stored procedure we created earlier. sdbConnString is a global variable defined outside of the include file, in another server-side include file that is inserted into every ASP page in the web site, but we will come to this in good time.

Next we have the starting tags of our HTML table. The ASP code following is the start of our while loop which loops though the recordset rows and creates our table's rows and cells:

HTML with embedded ASP script comes next. Here we write the HTML of the table cell, inserting the hyperlink which the user will click to view goods within that music category. We append the CatId and Category Description to the end of the hyperlink's URL. The ASP page which this link navigates to can pick up the data from the ASP Request object's QueryString collection.  Note that Description has been coded with the escape method to ensure no confusion occurs when it is passed as part of a URL.  Characters such as the ampersand (&) are converted into their ASCII value so they are not confused with an ampersand which indicates another item of data in the URL.

Finally we come to the end of the while loop and table:

Save the include file as CategoryList.inc into the MusicMad directory you created earlier. The .inc extension is not compulsory for include files but it is the one recommended by Microsoft.

The Global Include File

Our next task is to create another include file which will be added at the start of all our ASP pages using the include directive. It contains a number of global constants and general functions.

At the very top of the file on a separate line by itself is an ASP preprocessing directive. This must be the first line and it must be separate from other ASP code or the page will fail. There are a number of ASP preprocessing directives, some of which we will come to later, but this particular one sets the default language for all ASP on this page to JScript:

Next a couple of global constants used in the web site are declared. The sdbConnString is our connection string we use in our ADO statements to connect to the database. I have used a DSN-less connection for ease of set up (there is no set up needed!). If you prefer, you can set up an ODBC data source which does make it easier to change data sources without changing any code.  Even if you never change your database you may change its location to another server, something you can easily do with an ODBC data source.

Most of the database connection string is self-explanatory. However some needs further explanation. The Provider is our database, here SQL Server 7. Initial Catalog is our database. In Data Source we have used a period (full stop). This is an alias for the local server, similar to using localhost for the local web server. If you find this does not work, for example if your SQL Server database is not installed or you are using a Win95/98 machine, then replace the period with the name of the SQL Server your database is installed on.

Response.Buffer = true buffers the sending of page content and has been used to allow us to change cookie values once the HTTP header has been written. When the response is buffered, the result of the ASP code (HTML and client-side script) is stored in the server's memory until either the end of the page is reached or a Response.Flush or Response.End methods are called.  Buffering also means that we can change a cookie in server-side ASP code even after the <HTML> tag, something otherwise disallowed.

Next we come to the code for the first of the two functions included with the include file. This is part of our web site's shopping basket functionality. It extracts cookie data for a particular stock item contained within the basket – the ItemId, which is the same as that defined in the database, is used for identifying items. Data held within the cookie for a particular item includes ItemId, Qty, ArtistName, Item Description and the Price of an individual item. It is contained in a single string which uses & to delimit data within an item and the £ to indicate the end of the item's data.

The getItemFromCookie functions counterpart is the setItemToCookie function. Its parameters are ItemData, an array containing ItemId, ArtistName, item Description and Price, and the current value of the basket cookie.

There are three situations the routine deals with:

Regular Expressions, a powerful feature of JavaScript versions 1.2 and above, and the string object's replace method are used to update an existing quantity. For example, if we had an ItemId of 12, with a current Qty of 2, ArtistName "REM", Description "Monster" and Price of 9.99 then the cookie for that item will look like:

Our regular expression created by the line new RegExp(lItemId + "&[0-9]+"), will be:

This will match any occurrences of ID12& and any number of digits (which make up the quantity). [0-9] indicates any character in the range 0 – 9 (i.e. any digit). The + indicates that one or more of the previous character, i.e. a digit, must follow.

Save this page as ServerSideGlobalDef.inc.

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