On Mon, Mar 9, 2009 at 5:02 AM, Tim Chase <django.us...@tim.thechases.com>wrote:
>
> Dave E wrote:
> > I have some data (page number references) that looks like this:
> >
> > 320, 387..90, 410, 500
> >
> > or (sustituting numerical .. ranges for conventional dashes)
> >
> > 320, 387-90, 410, 500, 634
> >
> > I'd just like to know the most Django-esque way of creating a model
> > for these?
> >
> > The requirements are:
> >
> > 1. they're all numbers, or ranges of numbers
> >
> > 2. there will be at least one - and an unknown number of other - page
> > numbers or ranges, but not more than (say) 30.
> >
> > I've looked through a lot of documentation (and custom fields), but
> > can't find a tidy solution. I know that SET is a MySQL enxtension, so
> > not handled by Django.
> >
> > The issue has to be related to that of creating a model for HTML meta
> > tags, except that these are all numbers or number ranges.
>
> There are some other details you omit:
>
> - how would you like to handle (or not-handle) overlapping
> ranges? ("100..150, 120, 145-155")
>
> - are ranges always specified the same way? (".." vs. "-")
>
> - do you need to be able to sort the contents by page number?
> (and how does that interplay with overlapping ranges if allowed?)
>
> - do you need to be able to find whether a given page is within
> the range of listed pages?
>
> - are page numbers always integers? (think Roman numerals used
> in pre-text matter, or appendices with page numbers like "B-13")
>
> A couple thoughts occur to me:
>
> 1) just use a regexp-field and store them as a text-field (since
> you have a predefined cap of 30 you can get a rough estimate of a
> max...3 chars + 2 range characters + 3 chars + 1 comma + 1 space
> = 10 chars per range, * 30 references = 300 chars). This allows
> for a small bit of validation, but doesn't offer much flexibility
> in terms of sorting/searching/overlaps. It does allow for the
> Roman/appendix numbering scheme, depending on how tight you make
> your regexp
>
> 2) create a model like
>
> class PageRange(Model):
> source = ForeignKey(SomeOtherModel)
> start = PositiveIntegerField()
> end = PositiveIntegerField()
> def __repr__(self):
> if self.end:
> if self.end > self.start:
> return "%s-%s" % (self.start, self.end)
> elif self.end < self.start:
> return "INVERTED RANGE [%s-%s]" % (
> self.start, self.end)
> return str(self.start)
>
> then perhaps do some population/checks on the save (start must be
> <= end; if end is Null, default to start; perhaps check for
> pre-existing ranges and see if these bounds fall within another
> one). This has advantages that you can sort them, perform better
> checks on them, querying against them is easier, you can
> aggregate them to find the count, and you're not limited to an
> arbitrary number like 30. Granted, many of these bits may not
> matter to you, but if you need the flexibility of any of them,
> the others come for free.
>
> Just a few pre-breakfast rambling thoughts...
>
> -tim
>
>
>
>
>
>
>
> >
>
I agree with Tim, the relational way to handle this is a seperate model that
stores individual page ranges.
Alex
--
"I disapprove of what you say, but I will defend to the death your right to
say it." --Voltaire
"The people's good is the highest law."--Cicero
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