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POHow do I know which child class a Django model object is when selected through the parent class?
 

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  1. POHow do I know which child class a Django model object is when selected through the parent class?
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    <p>I have a main <code>Event</code> class, and four event types. Each of them is a subclass of (at least) <code>Event</code>. On an event's detail page, I am adding a link back to the admin interface for a given event to save the time of searching in the admin. Unfortunately, regardless of child class, the events are selected from the parent <code>Event</code> class. My solution to this problem was to duck type, which I find to be absolutely awful in this instance. <strong>I am hoping there is a more elegant and easy-to-maintain solution to my problem.</strong></p> <p>Model:</p> <pre><code>class Event(models.Model): ... class ListedEvent(Event): .... class RSVPEvent(Event): .... class TicketedEvent(Event): .... class TicketedConcert(TicketedEvent): .... </code></pre> <p>To see event details, the URL passes a venue slug and event name slug. This is enough info to isolate a single event from the parent <code>Event</code> model across all the child events. It also lets me keep the event type out of the URL, making them simpler and more friendly.</p> <pre><code>@render_to('events/event_details.html') def event_details(request, venue, slug): """ Detail view of an event. """ try: event = Event.objects.select_related( 'listedevent', 'rsvpevent', 'ticketedevent', 'ticketedconcert', 'venue', 'sites', 'dj', ).get( slug=slug, venue__slug=venue, ) except Event.DoesNotExist: raise Http404 return {'event': event} </code></pre> <p>Before I went back and realized that I was using the parent <code>Event</code> model, this solution was much more elegant and worked fine in the shell assuming I select an event from its actual model (property of parent class <code>Event</code>):</p> <pre><code>@property def admin_link(self): et = self.__class__.__name__.lower() # ALWAYS: et == 'event', reverse() fails, returns '' return reverse('admin:events_%s_change' % et, args=(self.id,)) </code></pre> <p>My current solution (property of parent class <code>Event</code>):</p> <pre><code>@property def admin_link(self): duck = None try: duck = self.ticketedevent.ticketedconcert.artist_name return reverse( 'admin:events_ticketedconcert_change', args=(self.id,) ) except: pass try: duck = self.ticketedevent.max_tickets return reverse( 'admin:events_ticketedevent_change', args=(self.id,) ) except: pass try: duck = self.rsvpevent.total_rsvp return reverse( 'admin:events_rsvpevent_change', args=(self.id,) ) except: pass try: duck = self.listedevent.name return reverse( 'admin:events_listedevent_change', args=(self.id,) ) except: pass </code></pre> <p>There has to be a simpler, more easy-to-maintain method of finding out which type of event I'm looking at. Any ideas?</p>
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    1. USJon Clements
    1. USBryson
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