Hi Mike,
Easily done, and no need to use signals or raw SQL: just override the save
method on your model so that every time you call save, the value in the baz
column is updated.
class Foo(models.Model):
bar = models.CharField()
baz = models.CharField()
def save(self, *args, **kwargs):
self.baz = function(self.bar)
return super(Foo, self).save(*args, **kwargs)
As a warning, there are some times when this won't work. For example, baz
won't be updated if you use a .update() call on a queryset, and it won't be
updated if you load a fixture or perform a "raw" save. However, this would
also be true of a signal based approach. For most simple uses, it should be
fine.
Yours,
Russ Magee %-)
On Thu, Oct 25, 2012 at 10:12 AM, Mike Burr <ad...@unintuitive.org> wrote:
>
> I would like to accomplish the following:
>
> class Foo(models.Model):
> bar = models.CharField()
> baz = function(self.bar)
>
> Of course this doesn't work (at least as I want it to), but I'm guessing
> that most humans will know what I'm trying to do. What I want is:
>
> 1) User supplies value for 'bar'
> 2) User clicks 'Save'
> 3) baz column gets value returned by 'function' (which will be a large
> string)
>
> I don't care if 'baz' shows up on the Admin form, so long as after saving
> the calculated value shows up. I could probably do this with a DB trigger,
> but I'd like to do it the Django way. A trigger would also not be
> RDBMS-neutral I considered using signals, but:
>
> 1) I don't think I can use pre_save, since I don't have a row yet.
> 2) I don't think I can use post_save because I don't know of a way to
> identify the right row. Also, post_save would make the transaction
> non-atomic (right?) If "function" threw an exception for example, the row
> would still get saved.
>
> If I do use a signal, I'd also like to avoid using raw SQL if possible.
> I'd have to hard-code table, column names, which seems ugly to me. I just
> know there's a quick, elegant way of doing this. I'm just not Django savvy
> enough yet.
>
> Thank you!
>
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