Django practice with external key queries

Question

models.py

class Category(models.Model):
    name = models.CharField(max_length=50)

class SubCatergory(models.Model):
    parent_category = models.ForeignKey(Category)
    name = models.CharField(max_length=100)

views.py

def all_products(request):
c = Category.objects.all()
s = SubCatergory.objects.all()

return render_to_response('all_products.html',
                          {'c':c, 's':s})

all_products.html

{% for category in c %}
    <h1>{{ category.name }}</h1>
    <ul>
        {% for sub in s  %}
        {% if category.id == sub.parent_category.id %}
            <li>{{ sub.name }}</li>
        {% endif %}
        {% endfor %}
    </ul>
{% endfor %}

Just wondering if the above is the best practice for foreign key requests. I am filtering at the template level (if category.id == sub ...), should this be transferred to the model or presentation level?

Answer 1

If there is only one subcategory depth, the following code should not be a problem:

{% for category in c %}
    <h1>{{ category.name }}</h1>
    <ul>
        {% for sub in category.subcatergory_set.all %}
            <li>{{ sub.name }}</li>
        {% endfor %}
    </ul>
{% endfor %}

But there are a few optimization tricks to reduce the number of queries, as you will be making a request per cycle. Now I'm trying to think about it.

Actually, I am starting to think that this is an interesting question: best practice?

2 . django, .

, , , , SubCatergory, , Category.

.

Answer 2

, . , .

templatetags/show_categories_list.py

from django.core.cache import cache

@register.simple_tag
def show_categories_list():
    cached = cache.get('CATEGORIES_LIST_CACHE_KEY', None)
    if cached is None:
        categories = Category.objects.all()
        rendered = render_to_string('all_categories.html', {'categories': categories})
        cache.set('CATEGORIES_LIST_CACHE_KEY', rendered)
        return rendered
    return cached

,

all_categories.html

{% for category in categories %}
    <h1>{{ category.name }}</h1>
    <ul>
        {% for sub in category.subcategory_set.all %}
            <li>{{ sub.name }}</li>
        {% endfor %}
    </ul>
{% endfor %}

, - ( , (pre | post) _save):

models.py

class Category(models.Model):
    name = models.CharField(max_length=50)

    def save(self, *args, **kwargs):
        cache.delete('CATEGORIES_LIST_CACHE_KEY')
        return super(Category, self).save(*args, **kwargs)

class SubCatergory(models.Model):
    parent_category = models.ForeignKey(Category)
    name = models.CharField(max_length=100)

    def save(self, *args, **kwargs):
        cache.delete('CATEGORIES_LIST_CACHE_KEY')
        return super(Category, self).save(*args, **kwargs)

, , :

base.html

{% load show_categories_list %}
{% show_categories_list %}

- , , , .

:

http://docs.djangoproject.com/en/1.2/howto/custom-template-tags/#shortcut-for-simple-tags http://docs.djangoproject.com/en/1.2/topics/cache/#the-low-level-cache-api http://docs.djangoproject.com/en/1.2/topics/signals/

Answer 3

, ? : .