#19427: Lacking Documentation on Custom Related Fields Pre-Save Override
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Reporter: s.shanabrook@… | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 1 | UI/UX: 0
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The process to create a custom field that inherits a `OneToOneField` or a
`ForeignKey ` (and I assume a `ManyToManyField` as well) and overrides the
`pre_save` method, is not clear in the documentation.
[https://docs.djangoproject.com/en/dev/howto/custom-model-fields
/#preprocessing-values-before-saving The section] that outlines how to
override the `pre_save` method says that the attribute name is
`self.attname`, when in fact on a related field, `self.attname` is the
model's id field for the related object.
So in order to actually modify the related object and then save it, you
must do something like this:
{{{
#!python
class CustomRelatedField(ForeignKey):
def pre_save(self, model_instance, add):
related_object = getattr(model_instance, self.name)
# Do stuff with object, custom saving
id = getattr(related_object, 'id', None)
setattr(model_instance, self.attname, id)
setattr(model_instance, self.name, redirect)
return id
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/19427>
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