I'm not sure I completely understand the problem, but I'll give it a
stab:
events = Event.objects.filter(start__gte=datetime.today())
locations = Location.objects.filter(location__in=events)
results = [
{'start': loc.location.start, 'title': loc.location.title, 'id':
loc.location.id, 'state_id': loc.state.id, 'name': loc.name} \
for loc in locations.iterator()
]
render_to_response('template.htm', {'results': results})
I run a query similar to this one on a 50,000 record table and it only
takes ~0.30 seconds, and that includes Json serialization!
On Jun 17, 5:00 pm, Sam Walters <mr.sam...@gmail.com> wrote:
> Here is the essentials from my models.py file:
> --------------------------------------------------------------------------------------------------------
> class Event (models.Model):
> contact = models.CharField(max_length=100)
> email = models.CharField(max_length=100)
> url = models.CharField(max_length=100)
> title = models.CharField(max_length=100)
> start = models.DateTimeField('date time when')
> end = models.DateTimeField('date till')
>
> class Location (models.Model):
> name = models.CharField(max_length=50)
> state = models.ForeignKey(State)
> location = models.ForeignKey(Event)
> --------------------------------------------------------------------------------------------------------
> This is a One-to-Many Relationship where an Event can have one or more
> Locations.
>
> The problem i need to solve is in the 'views.py' I want to be able to
> query 'Event' such that i retrieve an arbitrary subset of events AND
> any associated Locations and return only the relevant fields to the
> template layer.
>
> The most standard use for this database will be to get all events from
> today into the future and their associated locations. On average there
> would be say 25 event rows returned and perhaps 27 locations as some
> events have more than one location.
> --------------------------------------------------------------------------------------------------------
> e_future = Event.objects.filter(start__gte = datetime.today())
> --------------------------------------------------------------------------------------------------------
> having readhttp://docs.djangoproject.com/en/dev/topics/db/queries/
>
> i realise i can use a reverse foreign key to access an item in the
> Location table:
> --------------------------------------------------------------------------------------------------------
> for e in e_future:
> e_location=e.location_set.all()
> --------------------------------------------------------------------------------------------------------
> From here it gets messy as i have to deal with the individual event
> elements 'e' out of a queryset 'e_future' and then reassemble the
> elements back into a queryset *i dont know how to do this* so my
> method can return the selected columns:
> --------------------------------------------------------------------------------------------------------
> e_future_subset = e_future.values('start', 'title','id',)
> e_location_subset = e_location.values('state_id', 'name',)
> --------------------------------------------------------------------------------------------------------
> Then i have to combine the two objects 'e_future_subset' and
> 'e_location_subset' (which i believe are dictionaries) and return the
> result.
> --------------------------------------------------------------------------------------------------------
> e_all = e_future_subset + e_location_subset
> return render_to_response('events.html', { 'e_all': e_all,})
> --------------------------------------------------------------------------------------------------------
>
> As you can see I have been researching the solution and i'm stuck only
> on a couple of points.
> Surely this is one of the most common requirements for a django setup
> where the 'model.py' describes a number of related tables 'one-to-
> many' 'one-to-one' or 'many-to-many' relationships, a query (or number
> of queries) are made and results are returned from multiple tables
> based on an entry's 'id' and accessed through foreign-key pointers.
>
> Any help would be greatly appreciated as I seem to have a handle on
> everything else in my django project.
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