Question

as a very much of a newbie in Django/python world I fail to find a way to check whether an object has children.

An example:

Class MyItems
        title = models.CharField(max_length=50)
        parent = models.ForeignKey('self',null=True, blank=True,related_name='subitems')

Then in my template:

{% for item in MyItems %}
<li> {{ item.title }} </li>
    {% if item **IS A PARENT OF CHILDREN** %}
        <p>This is what I want</p>
    {% endif %}
{% endfor %}  

I can see if an item has a parent no problem, but how to do it other way around, tell if an item is a parent to other item?

Thanks!

Answer 1

if you want a recursive parent child relationship between your objects you should look at using MPTT

http://django-mptt.github.com/django-mptt/

<ul class="root">
{% recursetree nodes %}
    <li>
        {{ node.name }}
        {% if not node.is_leaf_node %}
            <ul class="children">
                {{ children }}
            </ul>
        {% endif %}
    </li>
{% endrecursetree %}
</ul>

talked about in the cookbook here:
https://code.djangoproject.com/wiki/ModifiedPreorderTreeTraversal

to understand how MPTT works at a data level, have a look at http://en.wikipedia.org/wiki/Nested_set_model

The problem with the obvious solution, is that for each additional level children, another query is required – which gets extremely inefficient.

# this is an additional query AND will not be recursive.
{% if item.child_set.all.count > 0 %}