Re: Query overhead or not ?

I look at aggregation and annotation but I don't think It's possible to solve this by using any of those two systems.
Or am I overlooking something ?

Op 31-aug-2010, om 13:09 heeft Jonas Geiregat het volgende geschreven:

> Thanks for your advise. I'm short of time right now so I briefly looked at django's aggregation possibilities.
> I'll look into them more deeply tonight.
>
> But I stumbled upon a problem.
>
> Post.objects.values('tags')
>
> Gives me:
>
> FieldError: Invalid field name: 'tags'
>
> In [56]: Post.tags
> Post.tags
>
> In [56]: Post.tags
> Out[56]: <django.db.models.fields.related.ReverseManyRelatedObjectsDescriptor object at 0x78f9f0>
>
> Post.tags does exist. Maybe it's because it's a ManyToManyField ? So I tried Post.objects.values('tags__name'). Still got an error ?
>
> I'm wondering why ?
>
> Op 31-aug-2010, om 09:28 heeft Jirka Vejrazka het volgende geschreven:
>
>>> tags = Tag.objects.all()
>>>
>>> for t in tags:
>>> indexed_tags[t] = Post.objects.filter(tags__name=t).count()
>>>
>>> Next I would sort indexed_tags and I have a dictionary of which tags are used the most.
>>>
>>> I'm wondering if this is a good idea ? Since if I have 1000 tags this would require 1000 queries just for one simple tag cloud.
>>> Is there a better way of solving this without adding an extra count field to the Tag model.
>>
>> Hi Jonas,
>>
>> your gut feeling was correct - it's not a very good idea, although
>> it might work for a small site. You might want to take a look at
>> database aggregation in Django:
>> http://docs.djangoproject.com/en/1.2/topics/db/aggregation/
>>
>> Cheers
>>
>> Jirka
>>
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>
> Met vriendelijke groeten,
>
> Jonas Geiregat
> jonas@geiregat.org
>
>
>
>
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Met vriendelijke groeten,

Jonas Geiregat
jonas@geiregat.org

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