In this second article, dive a little deeper into theintricacies of DTML by getting up close and personal with conditionalstatements and comparison operators. This article discusses thedifferent variants of the "if" statement available in DTML, togetherwith examples and code listings that demonstrate how they can be used ina Web applications.
You'll have noticed that in all the examples shown thus far, we've usedtwo Zope objects - a single DTML Document containing the form, and aseparate DTML Method which processes the form input and generatesappropriate output. However, DTML provides an elegant method to combinethose two pages into one via the "submit" variable.
In order to better understand this, create a new DTML Document named"DualPurposeForm" and add the following DTML code to it:
Welcome to Earth, <b><dtml-var species missing="Alien"></b> from the
planet <b><dtml-var planet missing="Zorgo"></b>.
How was your journey? Travelling <b><dtml-var distance missing="so
many"></b> light years must be quite a shock to the system. Why don't
you relax and have a drink?
In this case, the DTML "if" test will first check to see if the "submit"form variable exists. If it does, it implies that the form has beensubmitted, and the second half of the script, the actual form processor,comes into play. If it doesn't, it implies that the form has not yetbeen submitted, and so the initial, empty form is displayed.
This technique makes it possible to reduce the number of objects used,and perhaps make your Zope object collection easier to handle.
And that's about it for the moment. In this article, you learnt a littlemore about DTML, specifically about how to introduce decision-makinglogic into your Methods with DTML's numerous conditional statements. Youlearnt about the "if" and "unless" series of conditional statements, andsaw a few examples of the different variants possible. Finally, you sawhow all that theory can be put to practical use by implementing a simpleform processor for use on a Web page.
In the next issue of DTML Basics, I'll be rounding out the fundamentalswith a look at the various loop constructs provided by DTML. As witheverything you've seen so far, DTML comes with its own twist (pardon thepun) on the traditional way of implementing loops. Come back next timeto see what I'm talking about...and, until then, go practise.
Note: All examples in this article have been tested on Linux/i586 withZope 2.5.0. Examples are illustrative only, and are not meant for aproduction environment. Melonfire provides no warranties or support forthe source code described in this article. YMMV!