Hey,
I might have some ideas now. I have not understood the problem earlier.
On Wed, 2008-05-07 at 12:52 +0200, Christopher Mutel wrote:
> Hello all-
>
> I have tried a couple of tips found on the list to solve my problem
> with circular model imports, but with no lucks. Here is my basic
> schema:
>
> #foo/models.py
>
> from bar.models import Formula
>
> class Variable(models.Model):
> amount = models.FloatField(null=True)
> is_formula = models.BooleanField(default=False)
> formula = models.OneToOneField(Formula, null=True,
> related_name="variable_formula")
>
> def get_amount(self):
> if self.is_formula:
> return self.formula.evaluate()
> else:
> return self.amount
>
> #bar/models.py
>
> from foo.models import Variable
>
> class Formula(models.Model):
> formula = models.TextField() # Where formula is a text string like
> 'var:1337*var:42', and the numbers are id numbers.
>
> def calculate(self):
> # re stuff
> for each_found_variable in groups(): # Simplified to show process
> - this obviously doesn't work.
> raw_string.append(Variable.objects.get(id=this_id).get_amount())
> return eval(raw_string, stuff_to_make_eval_safe)
>
> In this case, the circular reference occurs only in a method of the
> class - I don't know if this makes a difference. How can I structure
> my import statements so that this is possible? I should note that
> there are more than one variable, so that combining everything into
> one models file is not really possible (and doesn't really address the
> chicken/egg problem either).
>
> I thought I saw a recent svn commit that addressed this problem, but
> can't find it now.
>
> Any help would be greatly appreciated?
>
The commit you refer to might be something from the now merged qs-rf
branch, where you can specify models from other django applications with
a new syntax like ForeignKey('app.Variable')
I can think of two methods of loading Variable inside your calculate
function:
- Write the import statement in the function instead of writing it at
the top of the module.
- Use django.db.models.loading.get_model('app', 'Variable')
I hope that helps,
Matthias
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