Can you make a custom template tag that returns a queryset? If yes, how? - Django

Question

Let's make this very easy for my fellow SOians(?).

This is how normally the custom template tags work -

Template ->

{% block content %}

     blah blah blah

     {% custom_tag_load %}

{% endblock %}

The custom_tag_load is called and it returns a string. What I want to return is a queryset which I could possibly use like this ->

{% block content %}

     blah blah blah

     {% for x in custom_tag_load %}

          {{ x.datetime }}

     {% endfor %}

{% endblock %}

Note -> What I'm basically trying to do is to avoid passing the queryset through the view, and I'm not sure if I should be comfortable storing querysets in my global context.

Answer 1

You can return anything you like from a tag, including a queryset. However, you can't use a tag inside the for tag - you can only use a variable there (or a variable passed through a filter). What you could do is get your tag to put the queryset into a variable in the context, and use that variable in the for loop. See the docs on how to set a variable from a tag - although note that the development version has an easier method for doing this.

However, you shouldn't be concerned about putting a queryset into a context processor, either. Don't forget that querysets are lazy, so no database hit will be made unless the queryset is evaluated or iterated in the template.

Answer 2

A template tag can do whatever you want. From your pseudo code, you could accomplish what you need with an inclusion tag:

#my_tags.py
from django import template
from my_app.models import MyModel

register = template.Library()

@register.inclusion_tag('my_template.html')
def my_custom_tag():
    things = MyModel.objects.all()
    return {'things' : things}


#my_template.html
{% if things %}
    <ul>
    {% for thing in things %}
        <li>{{ thing }}</li>    
    {% empty %}
        <li>Sorry, no things yet.</li>
    {% endfor %}
    </ul>
{% endif %}


#the_view.html
{% load my_tags %}

{% my_custom_tag %}

Alternatively, you could write a custom tag that adds a queryset to the context. Hope that helps you out.