Template Technologies: Mix them in your app

The 10gen platform was recently written about in the German "Jaxenter" online magazine:

http://it-republik.de/jaxenter/artikel/10gen-Komplette-Plattform-zum-Ablauf-von-Webanwendungen-1871.html

It's a nice writeup (as far as I can tell from the Yahoo! Babelfish! translation!) and kudos to the author, who I think did a good job - he downloaded the SDK and actually took it for a test drive.

One of the things that I appreciated  was that he grokked the idea that you can mix template styles in the app (forgive the Babelfish translation...):

"An interesting realization, which one can gain from this simple example, is those that the different Template technologies can be mixed with one another."

He didn't elaborate further, but I think that this is an important aspect of our technology - the appserver supports the use multiple template technologies seamlessly and simultaneously in an application. 

If you look at the "samplesite" demo app that comes with the SDK, you'll see the following [trivial] example of this in controller.jxp where the code calls three different templates and passes each data (template1, template2 and template3 in the templates directory of the application) to render into the output stream:

local.templates.template1({ theCount : data.count})
local.templates.template2({countThis : data.count})
local.templates.template3({ countThat : data.count})

Note that the variable name is changed to show that each template is independent....  What you don't need to worry about as a programmer here is that these three templates are actually of different types.  "template1" is a djang10 template, "template2" is a jxp, and "template3" is 10gen html.

Briefly, the 10gen appserver supports:

1. djang10 : this is a re-implementation of the great template system from the Django web application platform.   We really like Django, and are re-implementing it as fast as we can, as accurately as we can.
2. jxp : similar to the deservedly-maligned JSPs, where you mix markup and actual JavaScript in the same document
3. html : another 10gen-invented template, it's like jxp with added enhancements for in-line data access via $variable_name.  It was the first templating system that we did (we wanted to make it easy to mix data into existing HTML) and if you are starting fresh, we suggest that you use djang10.
   

So why is this important?  Well, I'd never advocate that one goes and starts building an application with multiple template styles out of the gate, but  software re-use is important in keeping project construction and maintenance costs under control, and supporting multiple template styles as first class citizens for an application helps with this goal.  This will make it easer to reuse app components, irrespective of the template style chosen by the author.

Note also that this part of our architecture allows for easy evolution and customization as this system is pluggable - you can easily implement other template styles, plug them into the appserver, and they can be first class templates as well.  To see how this works, go look at

ed.appserver.templates.TemplateEngine.java

in the appserver.  (Look in the nightly source download). I'm hoping someone contributes a support for my favorite template engine. ;)

Next time, I'll talk about mixed languages - how your app can use JavaScript and Ruby (and Python, even though Eliot doesn't want me to mention it as it's really not ready.  But you can try it.  Download the SDK...) code at the same time, in the same app.