Re: Model method versus overriding save()

On 12/8/12 5:37 AM, Derek wrote:

Rather than use a trigger (which is DB-specific and also hard to debug because not part of your code base), suggest you use signals[1].

Hmm. Triggers have advantages over application-level code where they can be used. They are likely more efficient (no data needs to be transferred to the client) and are more likely to ensure data integrity (by operating within a database transaction in an atomic fashion, and without application-level edge case failures). For cases like this one, debugging should be pretty easy because one can add or increment values in a table and watch the trigger do the additional work.

That's not to say that signals aren't a great feature, just that compact trigger code can have advantages and, well, that code is part of the code base too.

                              - Tom

Derek

[1] https://docs.djangoproject.com/en/dev/topics/signals/

On Saturday, 8 December 2012 04:27:50 UTC+2, Chris Cogdon wrote:

It's a simple performance vs storage question.

Storing a calculatable field also risks it getting out of sync with reality, but if you're doing the query on that _so_ much, then its usualyl worth it.

Also, with the right database and a trigger, that's something the database can ensure for you. Ie, a field that the database updates for you.

On Friday, December 7, 2012 5:54:37 PM UTC-8, Victor Hooi wrote:

Hi,

I have a "ranking" field for an item that returns an integer between 1 to 10 based on a number of criteria of each item.

My question is - what are the pros and cons of using a model method to return this, versus overriding the save() method and saving it directly into a normal IntegerField on that item?

I understand that model methods won't let me use them within QuerySet filters on that item - is there any way around that?

If I just override the model's save() method to get it recalculate and save that field each time, I can use it within QuerySet filters. Any cons with that approach?

What do you guys tend to use in your projects?

Cheers,

Victor

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