Blog « iKraft Software

A common task in a web developer’s day to day work is to add an ‘active’ class to anchor tags for styling the link to currently active page. In PHP world, this generally involves an if-else chain. But how do we do it in Django?

I searched the web but couldn’t find anything specific; therefore I coded a simple template tags for the purpose.

This little template tag can be used both with url names as well as the actual url strings. Check them out.

Here is the template tag code.

and here is how to use it in your templates.

Today, when I tried creating a new virtual environment for a project, it failed with the following error.

I guessed that it should have something to do with replacement of setuptools with distribute recent versions of virtualenv(because it could not find easy_install executable) and since as we know that python packaging is outdated and brain dead on Linux distos(at least on Ubuntu in my case), I upgraded the virtualenv installation with following commands:

And as it turns out my guess was correct and upgrading the relevant packages fixed this problem.

Recently I faced a problem in one of our Django project where I had to display drop down select box and checkboxes on a webpage which on initial page load had a about 20 - 30 choices. These choices could change via Ajax depending on the actions performed by the user. Also the choices come from a pool of hundreds of thousands of possible values.

Default forms.ChoiceField provided by Django, requires a list(or a tuple) of pairs of possible choices to be provided in the choices argument as follows.

The value of choices argument is used to build the html widget as well as for validating the form field. Therefore, if the submitted value for the my_choice_field is not present in the list_of_choices, an error is flagged and the form submission is not valid. Now we could not pre create a list with hundreds of thousands of possible values because of the obvious memory usage concerns and also the fact that we would have to modify the rendering logic of the widget to a very large extent which would have been time consuming both in terms of development & debugging.

For our particular use case, we solved this issue by subclassing forms.ChoiceField and overriding its valid_value method as described in following code snippet.

The valid_value method is fired to validate the value of the ChoiceField received through the form submission. The default definition of this method simply checks the presence of the received value in the choices list provided during the definitions of form class. By overriding this method and adding our own logic to check for the validity of received value we solved this issue with simplicity and minimal time investment.

PS: We could not use the django validators system for this purpose because in the case of ChoiceField, validators are fired after valid_value method.

After going through lot of custom functions for generating ordinal number in PHP, I was finally able to find the best way (so far) for doing it.

What’s happening here?

1. Since the PHP date function only considers valid number range from 1 to 31 for the day parameter, the modulo operator keeps it in this rang.
2. The number that has to be shown as the ordinal as 4th parameter to the mktime function.

I hope this saves someone’s time.

This post is in continuation to Multisite Installation In Drupal 6.

In the previous post mentioned above, we were using separate databases for each site within the same drupal core. There will be requirements where you will be required to have a single database to be shared among multiple drupal site installs. One important requirement being sharing of user access. It will be quite possible that multiple sites setup on same drupal core will want to share the user base. Also, it will be important that user login sessions be shared among those multiple sub sites. Under these circumstances, you will be required to have a single database with some of the tables (if not all) to be shared among the sub sites.

Below are the steps to do that assuming you have one sub site configured like http://example.com/subsite1/ using database ‘example_db’, and you create another sub site like http://example.com/subsite2/ to use same database. Just before running install.php for subsite2 make below mentioned changes to /subsite2/settings.php file by setting $db_prefix as an array like below

# /subsite2/settings.php
$db_url = 'mysql://user:pwd@localhost/example_db';
    
$db_prefix = array(
     'default'   => 'subsite2_',
     'users'     => '',
     'sessions'  => '',
     'authmap'   => '',
);
# By setting $db_prefix array like above, we are prefixing every other table with 'subsite2' except for 'users', 'sessions' and 'authmap' tables thereby marking them as shared.

The other way of doing the same thing will be to specify non shared tables like

# /subsite2/settings.php
$db_url = 'mysql://user:pwd@localhost/example_db';

$db_prefix = array(
     'default'   => '',
     'users'     => 'subsite2_',
     'sessions'  => 'subsite2_',
     'authmap'   => 'subsite2_',
);
# By setting $db_prefix array like above, we are sharing every table between 'subsite1' and 'subsite2' except for 'users', 'sessions' and 'authmap' tables.

Now, you should be ready to run install on subsite2.

Nutshell: The only important point for using a single database between multiple drupal sites with some or none shared tables is the ability to specify shared/non shared tables which is as simple as specifying list of tables within $db_prefix as key/value pairs.

Note: if you want to have single database to be used between multiple drupal sites with no tables shared, just specify table prefix as

$db_prefix = 'subsite2_';

Assuming you have basic drupal 6 installation already working on a LAMP server. Below are the steps to setup multiple sites to work on same drupal core like site1.com, site2.com etc.

Create site databases Start by creating databases for each site like site1, site2 etc thereby setting specific credentials to each database created.

Setup drupal site configuration directories Copy and paste /sites/default directory and rename the copied directories to /sites/site1.com, /sites/site2.com directories. The only important file from the /sites/default directory being settings.php, you can skip all the other files/directories while copying /sites/default directory. Although, later on you might need to create several different directories within each site directory like files, modules, themes etc contents of whom will be specific to that site. Edit settings.php file of each site and set database details specific to each site.

Create virtual hosts for each site under Apache2 Steps for creating virtual hosts under debian/ubuntu based systems. Open terminal use below commands

$ cd /etc/apache2/sites-available
$ sudo gedit site1.com

Put below contents within this file

<VirtualHost 127.0.1.5:80>
    ServerAdmin webmaster@localhost
    ServerName site1.com

    DocumentRoot /home/umar/Work/htdocs/drupal6
    <Directory />
        Options FollowSymLinks
        AllowOverride All
    </Directory>
    <Directory /home/umar/Work/htdocs/drupal6>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride All
        Order allow,deny
        allow from all
   </Directory>
</VirtualHost>

Now enable the site with following command

    
$ sudo a2ensite site1.com

Repeat the above steps for all sites with unique local IP’s for each site. When done with creation of all files reload apache

$ /etc/init.d/apache2 reload

Now edit the /etc/hosts file to include mapping of these new sites like

$ sudo gedit /etc/hosts

With contents like

127.0.0.1  localhost
127.0.1.5  site1.com
127.0.1.6  site2.com

Thats all there is to it, now go to url like http://site1.com/install.php of each site and follow normal drupal installation procedure.

I will soon be posting article showing usage of single DB between multiple drupal sites configuration.

Cheers