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PODjango: how to add a non-database object to query results
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  1. PODjango: how to add a non-database object to query results
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    copied!<p>Let's consider a situation where I have a bunch of people who own some shirts:</p> <pre><code>class Person(models.Model): name = models.CharField() class Shirt(models.Model): description = models.CharField() owner = models.ForeignKey(Person) </code></pre> <p>I take portrait photos of them in one of their shirts:</p> <pre><code>class Photo(models.Model): person = models.ForeignKey(Person) shirt = models.ForeignKey(Shirt) </code></pre> <p>In templates I use stuff like</p> <pre><code>{{ the_photo.shirt.description }} </code></pre> <p>and</p> <pre><code>{% for shirt in the_person.shirt_set.all %} {{ shirt.description }} {% endfor %} </code></pre> <p>I also have forms to let me pick a shirt for a photo from the model's inventory.</p> <p>Now, a twist! I can also take a photo of them without a shirt! So I want <code>the_person.shirt_set</code> to contain also a <code>description='topless'</code> entry in additional to any shirts they might own. I'd rather not store an additional <code>'topless'</code> shirt for each person and wouldn't like to have to modify each form and list to add this option.</p> <p>I had an idea of creating a <code>Topless</code> class:</p> <pre><code>class Topless(Shirt): def __init__(self, *args, **kwargs): super(Topless, self).__init__(*args, **kwargs) self.description = 'Topless' </code></pre> <p>and adding it to lists:</p> <pre><code>class Person(models.Model): name = models.CharField() def shirts(self): l = list(Shirt.objects.filter(owner=self)) l.insert(0, Topless()) return l </code></pre> <p>(and switching from <code>the_person.shirt_set</code> to <code>the_person.shirts</code> in templates of course), but it's getting ugly with <code>the_photo.shirt</code> since the id is None (or 0) and it looks like it will require a bunch of ugly hacks to accommodate for that.</p> <p>But maybe I'm doing it wrong? Any ideas? What's the most elegant and pythonic way to do it?</p>
 

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