在Django模板中访问临时模型数据？

Question

I have the following view code which adds some temporary data to a Django model instance contained within a ManyToMany relationship. I'd like to be able to access that data within the template but I'm not sure how.

@login_required()
def shopping_cart(request):
    try:
        cart = ShoppingCart.objects.get(user__exact=request.user)
    except ShoppingCart.DoesNotExist:
        cart = ShoppingCart(user=request.user)
        cart.save()

    for album in cart.albums.all():
        album.vat_rate = request.session['vat_rate']
        album.total_cost = (((album.price / 100) * album.vat_rate) + album.price)

    return render_to_response('sym_money/shopping_cart.html',
                          {'shopping_cart': cart},
                          context_instance=RequestContext(request))

I need to be able to access the vat_rate and the total_cost in the template by doing:

{% for album in cart.albums.all %}
    {{ album.vat_rate }}
    {{ album.total_cost }}
{% endfor %}

None of the temporary data has any fields in the model and I don't want to save it to the database either, I just want to be able to access the temporary data in the model from the templates.

Answer 1

In the template, when you do {% for album in cart.albums.all %} , you're creating a completely new queryset so your previous annotated objects are all discarded.

Save the album queryset as a variable in your view, iterate it and anotate the objects like you're doing, then pass this variable to the context.

Hint: render_to_response is oldskool - just use render .