python - 如何在模板中显示递归数据？

Question

我有一个 ForeignKey = 'self' 的模型，我想通过列表和子列表反射(reflect)数据库中的所有数据:

这是我的模型:

class Place(models.Model)
    name = models.CharField(max_length=128, verbose_name='Place name', )
    slug = models.SlugField(max_length=128, blank=True, null=True)
    parent = models.ForeignKey('self', on_delete=models.CASCADE, blank=True, null=True)
    role = models.CharField(max_length=20, choices=ROLE_CHOICES, null=True, blank=True) 

Answer 1

Django template is not designed to handle complex logics. For example, you can't write nested logic by using include tag like this:

# foo.html
{% if nodes|iterable %}
<ul>
{% for x in nodes %}
  {% include "foo.html" with nodes=x %}
{% endfor %}
</ul>
{% else %}
<li>{{ nodes }}</li>
{% endif %}

Because Django template nodes get parsed and compiled before they get rendered, and the compiling of the above code could fall into loops and fail by hitting maximum recursion depth.

Normally, a template tag just like {% nested nodes %}, which works like a view but belongs to the scope of Django template, is all you need.

Moreover, you could transform the data to a flat one through a filter, then loop over it easily:

{% for x in nodes|nested_to_flat %}
{% if x.start_nodes %}<ul>{% endif %}
{% if x.end_nodes %}</ul>{% endif %}
{% if x.start_node %}<li>{% endif %}
{% if x.end_node %}</li>{% endif %}
{% if x.is_data %}{{ x.data }}{% endif %}
{% endfor %}

# nested_to_flat
@register.filter
def nested_to_flat(nodes):
    if isinstance(nodes, list):
        yield {'start_nodes': True}
        for node in nodes:
            yield {'start_node': True}
            for i in nested_to_flat(node):
                yield i
            yield {'end_node': True}
        yield {'end_nodes': True}
    else:
        yield {'data': nodes, 'is_data': True}

This is similar to the idea of rendering a mptt tree or threaded comments.