Re: Query overhead or not ?

Tag.objects.values('name').annotate(times_used=Count('post__tags'))

That's the solution!

Op 1-sep-2010, om 15:00 heeft Jonas Geiregat het volgende geschreven:

> 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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Met vriendelijke groeten,

Jonas Geiregat
jonas@geiregat.org

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