On Wed, Dec 31, 2008 at 6:02 AM, bruno desthuilliers <
bruno.desthuilli...@gmail.com> wrote:
>
>
>
> On 31 déc, 05:40, schwim <gsch...@gmail.com> wrote:
> > I'm trying to build a model that will store the counts of each of 10
> > possible choices, e.g.:
> >
> > v1 = models.IntegerField(default=0)
> > v2 = models.IntegerField(default=0)
> > v3 = models.IntegerField(default=0)
> > ...
> > v10 = models.IntegerField(default=0)
> >
> > I'd prefer to represent this as an array
>
> Where ?
>
> > rather than 10 separate
> > fields. I looked at the CommaSeparatedIntegerField as an alternative,
> > but I want to explicitly state that there are 10 entries available per
> > instance.
>
> Note that at the Python level, a list (I suppose that's what you mean
> by 'array') is not fixed-length.
Yes, that is what I meant actually. I'm new to python, a perl convert I
guess you could say.
>
>
> If all you want is a way to access the values as a sequence (read-
> only) from your python/templates code, it's just a matter of adding a
> simple property:
>
>
> class YourModel(models.Model):
> # you code here
> @property
> def values(self):
> return [getattr(self, "v%s" % i) for i in range(1,11)]
>
>
> then:
>
> m = YourModel.objects.get(...)
> m.values
> m.values[0]
> m.values[9]
Yes, I think this would work nicely actually. I really only need to access
the values as a list when reading. Writes will be specific.
>
>
>
> If you want a reliable read-write property, this becomes a bit more
> involved. You have to write a custom descriptor returning a custom
> sequence type that retains a reference on the model instance.
>
> The following code should get you started - warning: it's Q&D, full of
> magic numbers, not generic, not factorized, and not even tested.
> IOW : it's by no mean production code.
>
> class MySequence(object):
> def __init__(self, model):
> self._model = model
>
> def _as_fieldname(self, index):
> # sequences are zero-based
> # XXX : magic number
> if not 0 <= index <= 9:
> raise IndexError
> # your fields are 1-based
> # XXX duplicated in MySequenceDescriptor
> return "v%s" % (index+1)
>
> def __getitem__(self, index):
> fname = self._as_fieldname(index)
> return getattr(self._model, fname)
>
> def __setitem__(self, index, value):
> fname = self._as_fieldname(index)
> setattr(self._model, fname, value)
>
> # you may need some other sequence __magicmethods__ here
> # check the Python's manual about emulating sequence types
>
>
> class MySequenceDescriptor(object):
> def __get__(self, instance, cls):
> if instance is None:
> # looked up in the class
> return self
> # looked up on a model instance:
> return MySequence(instance)
>
> def __set__(self, instance, value):
> # expects a sequence of len(10)
> # XXX : magic number
> if len(value) != 10:
> raise ValueError("yadda yadda")
> for index, val in enumerate(value):
> # XXX duplication of MySequence._as_fieldname
> setattr(instance, "v%s" % (index+1), val)
>
>
> class YourModel(models.Model):
> # your code here
>
> values = MySequenceDescriptor()
>
> HTH
>
>
Very helpful, yes, thank you. I think I understand your approach here, but
it's probably more complicated than I need.
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