Can Django support an update by setting a field to the least of two args?
I have a model that looks like:
class Bar
maxval = models.FloatField()
rate = models.FloatField()
class Foo(models.Model):
bar = models.ForeignKey(Bar)
current = models.FloatField()
and i'd like to increase current up to max by rate for every case
where it's not yet the max...
IE: I'd like to do something like:
Foo.objects.filter(current__lt=F('bar__maxval')).update(current=least(Q('current')+Q('bar__rate'),Q('bar__maxval')))
But that fails because you can't add 2 query sets together, can't join
field referenecs in an update, and I don't see support for 'least'
What I've done instead is rewritten it to iterate over bars each time
filtering on foo like:
set = foo.objects.filter(bar=bar).filter(current__lt=bar.max)
and then compute the min amount of current to hit max this update, and
update that, then iterate over what remains and update each one
individually, ie:
canreachfull = bar.max - bar.rate
set.filter(current__gte=canreachfull).update(current=bar.rate)
set = foo.objects.filter(bar=bar).filter(current__lt=bar.max)
for record in set:
newcurrent = record.current + bar.max
record.update(current=newcurrent)
Is there a better way to do this?
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