I have two models, Trade and Fill. A Trade can have many fills. Fill
has a FK to Trade:
class Trade(models.Model):
trade_date = models.DateField(auto_now_add=True, editable=False)
side = models.CharField(max_length=12, choices=SIDE_CHOICES)
inst = models.ForeignKey(Inst)
class Fill(models.Model):
trade = models.ForeignKey(Trade)
quantity = models.DecimalField(max_digits=12,decimal_places=2)
price = models.DecimalField(max_digits=13,decimal_places=6)
fees = models.DecimalField
(max_digits=10,decimal_places=2,blank=True,null=True)
counterparty = models.CharField(max_length=12)
time = models.TimeField()
note = models.CharField(max_length=200, blank=True, null=True)
I have a web page that shows information about a Trade along with a
table of all the Fills for that trade. It also includes a form for
adding new Fills.
The problem I ran into was that in my view function for saving a new
Fill, I need to have the Trade instance set for the form to validate.
But it doesn't make sense for the user to edit the Trade since it's
tied to the one on the page they were viewing, so the default
ModelChoiceField doesn't work for this case.
Instead I created a custom field that stores the FK Trade id in a
hidden field and then resolves it back to the actual Trade instance in
the clean method:
class ModelField(forms.CharField):
def __init__(self, rel, *args, **kwargs):
super(ModelField, self).__init__(
widget=forms.HiddenInput, *args, **kwargs)
self.rel = rel
self.queryset = self.rel.to._default_manager.complex_filter(
self.rel.limit_choices_to)
def clean(self, value):
forms.Field.clean(self, value)
if value in (None, ''):
return None
try:
obj = self.queryset.get(pk=value)
except self.queryset.model.DoesNotExist:
raise ValidationError('Object not found for id: %s' %
value)
return obj
(I stole most of this from ModelChoiceField). I use it like this:
class FillForm(forms.ModelForm):
trade = ModelField(Fill._meta.get_field('trade').rel)
class Meta:
model = Fill
While this works, it feels like I'm digging into the internals of
Django too much with the _meta.get_field() and use of rel and queryset
in the ModelField.
Does anyone see a simpler solution to this? I feel like I'm missing
something obvious.
Thanks,
-Dave
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