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POCan a Django model field's default value be defined by a function dependent on a foreign parent model?
 

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  1. POCan a Django model field's default value be defined by a function dependent on a foreign parent model?
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    <p>I'm trying to have the default value of <code>Report</code>'s fee be based on a parent model's attributes. I don't want to do this in <code>save()</code>, because the field needs to be presented to the user if they choose to override the value before saving.</p> <p>Here are the three methods I've tried, in addition to passing only function pointers (i.e. without <code>()</code>). The errors are raised when I run <code>python manage.py shell</code>.</p> <pre><code>#1 from django.db import models class Job(models.Model): veryImportant = models.IntegerField() def get_fee(self): return 2 * self.veryImportant class Report(models.Model): job = models.ForeignKey(Job) overridableFee = models.DecimalField(default=job.get_fee(), max_digits=7, decimal_places=2) #gives... #AttributeError: 'ForeignKey' object has no attribute 'get_fee' #2 from django.db import models class Job(models.Model): veryImportant = models.IntegerField() class Report(models.Model): job = models.ForeignKey(Job) overridableFee = models.DecimalField(default=self.set_fee(), max_digits=7, decimal_places=2) def set_fee(self): overridableFee = 2 * self.job.veryImportant #gives... #NameError: name 'self' is not defined #3 from django.db import models class Job(models.Model): veryImportant = models.IntegerField() def get_fee(): return 2 * veryImportant class Report(models.Model): job = models.ForeignKey(Job) overridableFee = models.DecimalField(max_digits=7, decimal_places=2) def __init__(self, *args, **kwargs): self.overridableFee = self.job.get_fee() super(models.Model, self).__init__(*args, **kwargs) #gives... #TypeError: object.__init__() takes no parameters </code></pre> <p>The error with #3 could be that I just have no idea how to override <strong>init</strong> properly. I copied something out of another answer and gave up after it didn't work.</p> <p>If none of these will work, I can always revert to just setting the fee after I create each Report in the view, but I'd rather do it automatically when the Report is created, for sanity.</p> <p>EDIT:</p> <p>Ended up going with #3, fixed with Yuji's answer and modified to make sure any possible fee set from the shell overrides what job.get_fee() wants.</p> <pre><code>def __init__(self, *args, **kwargs): super(Report, self).__init__(*args, **kwargs) if self.overridableFee == None and self.job and not self.pk: self.overridableFee = self.job.get_fee() </code></pre>
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