Question

I’m trying to use the in operator to determine if a template variable on the current page is also a foreign key in another model.

The model is like so:

class WishlistItem(models.Model):
    user  = models.ForeignKey(User, related_name='wishlist_items')
    issue = models.ForeignKey(Issue)

On the “Issue” page template, I’m trying to do this:

{% if issue in user.wishlist_items %}
{% else %}
    {# A button to add the issue to the user's wishlist #}
{% endif %}

What I need to do is to get at the issue attribute of the wishlist_items QuerySet for the currently logged-in user and compare it to the issue object of the current page. I’m at a loss for how to do this. Do I need to write a templatetag to do this?

Answer 1

I ended up solving this by writing a template filter:

@register.filter
def in_list(obj, arg):
    "Is the issue in the list?"
    return obj in (item.issue for item in arg)

Then I could do something like this in a template:

{% if issue|in_list:user.wishlist_items.all %}

I got the idea from the answer on this Stack Overflow question.