Question

I have a model called Subtopic. One of my templates runs a forloop on an object, returning a different field for each cell of a table row.

Two of the table cells look up a field which is a ManytoMany foreign key, both to the same foreign model, Resource. I want each to display different results, based on the value of a boolean field within the Resource model.

What you see below is currently working fine, but doesn’t attempt to filter by the boolean field.

models.py:

class ICTResourceManager(models.Manager):
    def get_query_set(self):
        return super(ICTResourceManager, self).get_query_set().filter('is_ict': True)

class NonICTResourceManager(models.Manager):
    def get_query_set(self):
        return super(NonICTResourceManager, self).get_query_set().filter('is_ict': False)

class Resource(models.Model):
    subtopics = models.ManyToManyField(Subtopic)
    external_site = models.ForeignKey(ExternalSite)
    link_address = models.URLField(max_length=200, unique=True, verify_exists=False)
    requires_login = models.BooleanField()
    is_ict = models.BooleanField()
    flags = models.ManyToManyField(Flag, blank=True)
    comment = models.TextField()
    def __unicode__(self):
        return u'%s %s' % (self.external_site, self.link_address)
    objects = models.Manager()
    ict_objects = ICTResourceManager()
    nonict_objects = NonICTResourceManager()

    class Meta:
        ordering = ['external_site', 'link_address']

views.py:

def view_ks5topic(request, modulecode, topicshortname):
    listofsubtopics = Subtopic.objects.filter(topic__module__code__iexact = modulecode, topic__shortname__iexact = topicshortname)
    themodule = Module.objects.get(code__iexact = modulecode)
    thetopic = Topic.objects.get(module__code__iexact = modulecode, shortname__iexact = topicshortname)
    return render_to_response('topic_page.html', locals())

My template:

        {% for whatever in listofsubtopics %}
        <tr>
            <td>
                {{ whatever.objective_html|safe }}
                <p>
                {% if request.user.is_authenticated %}
                    {% with 'objective' as column %}
                    {% include "edit_text.html" %}
                    {% endwith %}
                {% else %}
                {% endif %}
            </td>
            <td>
                {% regroup whatever.resource_set.all by external_site.name as resource_list %}
                {% for external_site in resource_list %}
                    <h4>{{ external_site.grouper }}</h4>
                    <ul>
                        {% for item in external_site.list %}
                        <li><a href="{{ item.link_address }}">{{ item.comment }}</a></li>
                        {% endfor %}
                    </ul>
                {% endfor %}
            </td>
        </tr>        
        {% endfor %}

As you can see, I’ve added extra managers to the model to do the filtering for me, but when I replace the appropriate lines in the template, I just get blanks. I have tried: for external_site.ict_objects in resource_list and for item.ict_objects in resource_list and <a href="{{ item.ict_objects.link_address }}">. If this were in the view I could probably do the filter just by .filter('is_ict': True), but with this being inside a forloop I don’t know where to do the filtering.

I also tried writing regroup whatever.resource_set.filter('is_ict': True) in the template, but the syntax for regrouping seems to use resource_set.all rather than resource_set.all() (and I don’t know why) so the filter text doesn’t work here.

Answer 1

Turns out it was possible to do it using a custom template filter. The original efforts to filter within the template weren’t working, given that as is well documented the template language is not a fully-fledged python environment. My original question remains open for anyone who knows an alternative method that more directly addresses the question I was originally asking, but here’s how I did it:

myapp_extras.py:

from django import template

register = template.Library()

def ict(value, arg):
    "filters on whether the is_ict Boolean is true"
    return value.filter(is_ict=arg)

register.filter('ict', ict)

My template, note the use of the custom filter in line 2:

<td>
    {% regroup whatever.resource_set.all|ict:1 by external_site.name as resource_list %}
    {% for external_site in resource_list %}
        <h4>{{ external_site.grouper }}</h4>
        <ul>
        {% for item in external_site.list %}
            <li><a href="{{ item.link_address }}">{{ item.comment }}</a></li>
        {% endfor %}
        </ul>
    {% endfor %}
</td>

After this I was able to remove the additional custom managers from the model.

One further question, when filtering for the boolean is_ict field, I found that I had to use filter(is_ict=1) and filter(is_ict=0). Is that the only way to refer to a True or False value?