Sunday, 18 March 2007

Django (python) vs. Catalyst (perl)


I spend many days with Perl MVC framework - Catalyst. Catalyst for perl is like Rails for ruby but without all this marketing hype & noise (and unfortunatelly with lack of good books, tutorials and doc). I tried to use Rails for some easy-but-existing database. I was surprised that Rails ActiveRecord was not able to quote SQL names to get data from - as I remember - "lines" column in MySQL. Little stupid, hmm?

Anyway Ruby is too perlish. I know perl and know how much cost all this TIMTOWTDI when your project is growing up. Python is like clean, better Perl (however Python libraries are not at this quality level like Perl libs in CPAN - eg. unicode translations). So this is "why python".

Few days ago I started small project with Django. Here are first thoughts and differences:

Django view = Catalyst controller

Django call itself MTV framework (model-view-template). Going this way Catalyst is Model-Controller-(View)-Template - the only difference is: Django models == Rails & Catalyst controllers.

Django global switch

- In Django you need to define every URL action in and create appropiate "views"

Example of (aka "global switch"):

urlpatterns = patterns('',
('', ''), # root page
(r'^admin/', include('django.contrib.admin.urls')), # admin
(r'^photo/update', ''), # update

- In Catalyst, there is no such "global switch". You just create controllers (perl classes), put methods with "local" attribute inside - and they are visible in your URL namespace. Why you should define this namespace mapping if it is enough to do it only by proper view class-function naming? For me it looks like Catalyst dispatcher is more "pythonic" than Django.

Output validation

I created view to import some data from Yaml data-dump to MySQL database. Everything works however Django cannot display some rows because of problems with validation. Message error is not so helpfull -

ValueError at /
year is out of range

Hmm, but which field (i have 2 dates in every record) in which row? Exception is caught in template (first line)

{% for repo in gallery_list %}
* {{ repo.galleryname }}
{% endfor %}

but as you see - I do not fetch any date-time values here!

After looking into data I found '0000-00-00' date. Who pasted this record into database without problems? Django db model. Who was not able to show it? Django! I think it's a better idea to validate/filter data at input rather than output. Or in both places.


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