> I'm in the process of turning telemeta [1] into a django
> application, and need dynamic model fields: we want to allow
> site administrators to easily add/remove "fields" to our main
> data structure, the MediaItem, which represents an audio/video
> resource.
>
> Example: for a given research laboratory the MediaItem may
> need to have a "musicians" field, but for another laboratory
> it can be "filmmaker", etc... And there may be dozens of these
> dynamic fields, which could be added/removed at any time.
>
> We believe the process of hard-coding those fields into the
> models is a developer task and too heavy for the
> administrators we target, especially because of the need to
> manually modify the SQL tables.
Our current app does something like this...our basic solution was
something like one of the two following ideas (depending on
whether particular categories should be consistent across labs,
such as "media" meaning the same thing in Lab1 and Lab2)
class Lab(Model):
pass
class Category(Model):
name = CharField(maxlength=40)
class LabCategory(Model):
lab = ForeignKey(Lab)
category = ForeignKey(Category)
class Values(Model):
category = ForeignKey(LabCategory)
value = CharField(maxlength=40)
class MediaItem(Model):
lab = ForeignKey(Lab)
values = ManyToMany(Values)
or the more simple "every lab has its own bag of categories that
don't relate to anybody else" (this is how we settled on it
because our clients rarely have much in common for these
category/value pairs):
class Lab(Model):
pass
class Category(Model):
lab = ForeignKey(Lab)
name = CharField(maxlength=40)
class Value(Model):
category = ForeignKey(Category)
value = CharField(maxlength=40)
class MediaItem(Model):
lab = ForeignKey(Lab)
values = ManyToMany(Values)
Thus, you can use something like (possibly bogus code, but the
idea applies)
for item in MediaItem.objects.all():
s = '%s: %s' % (item.lab, item)
print s
print '='*len(s)
for v in item.values:
print '\t', v.category.name, '=', v.value
It does require checking to ensure that a MediaItem has all the
Category values filled out for the given Lab (otherwise, it's
possible for a Lab to have 3 Category fields, but the user only
populates 2 of them), but that's an exercise to the reader (a
non-trivial task when you add new categories, what goes into the
category value for all existing data).
This doesn't involve any SQL monkeying once the system is in
production, but it still allows each Lab to have an arbitrary
list of its own Category/Values.
If you have archive data, you may also want to add an "active"
flag to both the Category and Value models so that you can retire
either, but still have the data in the system. Your
checks-for-all-categories should then take the Category's active
flag into consideration.
My $0.02 from my own feable experiences...
-tkc
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