How do web templates separate content and logic?

bruno.desthuilliers at gmail.com bruno.desthuilliers at gmail.com
Fri Jun 27 23:07:32 CEST 2008


On 27 juin, 18:09, "John Salerno" <johnj... at NOSPAMgmail.com> wrote:
> I've been doing some research on web templates, and even though I read that
> they help enforce the MVC pattern, I don't really understand how they are
> keeping content and logic separated.

For which definitions of "content" and "logic" ???

The point of mvc is to keep domain logic separated from presentation
logic, not to remove logic from presentation (which just couldn't
work). Templating systems are for presentation logic. Whether they
work by embedding an existing complete programmation language or by
providing they're own specialised mini-language (or a mix of both) is
not the point here IMHO.

>  Layout is easy, it's just not there as
> far as I can see, and CSS can be used for that.

You still have to generate the markup on which css will be applied,
don't you ?

> But when you have a templating system that mixes HTML and Python code, how
> is this helping to keep things separate? It seems to be the same issue that
> some people have with PHP (that it is too integrated with the HTML, rather
> than being separate).

Well... yes and no. The server page approach surely fails to make
clear what belongs to which layer. Now you still can produce "clean"
application using PHP - if you are disciplined enough and know what
you're doing. It's a bit like the "lack" of language-enforced access
restriction in Python - it's only a problem if you don't understand
why it's good to separate interface from implementation.

> Of course, I suppose whether or not any of this matters depends on if you
> are a web designer or a programmer, but am I missing something about
> templates, or is it really the case that they, more or less by definition,
> combine content and logic?

The real problem is not to avoid having logic in templates, but to
avoid mixing domain logic (which is independant from presentation) and
presentation logic. Using a templating system - whether it embeds
Python or use it's own mini-language - makes clear (well... clearer)
what belongs to presentation and what belongs to domain.




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