Question

I’m trying to figure out how to solve this

class Item(models.Model):
    type = models.ForeignKey(Type)
    name = models.CharField(max_lenght = 10)
    ...

class List(models.Model):
    items = models.ManyToManyField(Item)
    ...

I want to count how many an Item appears in another Lists, and show on template.

view

def items_by_list(request, id_):
    list = List.objects.get(id = id_)
    qr = list.items.all()

    #NOT TESTED

    num = []
    i = 0
    for item in qr:
        num[i] = List.objects.filter(items__id = item__id ).count()

    #FINISH NOT TESTED

    c = {}
    c.update(csrf(request))
    c = {'request':request, 'list' : qr, 'num' : num}
    return render_to_response('items_by_list.html', c, context_instance=RequestContext(request))

template

    {% for dia in list %}   
            <div class="span4" >
                <div>
                    <h6 style="color: #9937d8">{{item.type.description}}</h6>
                    <small style="color: #b2e300">{{ item.name }}</small>
                    <small style="color: #b2e300">{{COUNT HOW MANY TIMES THE ITEM APPEAR ON OTHER LISTS}}</small>

                </div>  
    {% endfor %}

This seems to be easy, but I could not implement yet.

If anyone has some glue to me, please help me.

Thanks in advance.

Answer 1

If you’re using django 1.3+, then use aggregation

from django.db.models import Count    
queryset = List.objects.annotate(item_count=Count('item'))

Each List instance in this queryset will have a item_count attribute, that you can display in your template. You’ll find more examples in docs.