gistfile1.py

from django import template # to handle templates variables and context
register = template.Library() # register our template tags to be able to use them in our templates

from events import models # to get the models of our app

class EventMetadataListNode(template.Node):
    def __init__(self, event_pk, context_var):
        self.context_var = context_var # new var we are going to create
        self.event_pk = template.Variable(event_pk) # the pk, get from the template "context" as a variable

    def render(self, context):
        # here we create a new context variable named from self.context_var and assign to it the result set
        # see the use of "resolve" that will get us the var from the context
        context[self.context_var] = models.EventMetadata.objects.filter(event__pk=self.event_pk.resolve(context))
        return ''

def do_get_event_metadata(parser, token):
    """
    get the event metadata

    Example::
        {% get_event_metadata event.pk as metadatas %}
    """
    # split the args string, it detects "quoted parameters" and doesn't stop on spaces
    bits = token.split_contents()
    if len(bits) != 4: # we check if we passed the right number of args
        raise template.TemplateSyntaxError(_('%s tag requires exactly 1 argument, and a variable') % bits[0])

    return EventMetadataListNode(bits[1], bits[3]) # bits[1] == events.pk, bits[3] == variable

# finally we register the new template tag
# first parameter is the name in the template the second one is the name in the source file
register.tag('get_event_metadata', do_get_event_metadata)