The error is occurring here as you have mentioned -
rolestartdate = models.DateField(default = \
Project.objects.get
(pk=project.id).startdate)
You're right that Django creates an attribute named id for every model
without a primary key explicitly specified, but I suspect the issue
here is that Django is trying to resolve 'project.id' before the
Project model has been fully initialized. Also, Django is trying to
resolve project.id for the model class, and not a model instance which
won't work as model classes do not contain data.
I believe 'default' can only be used to specify static values, not
values that depend on other models (there is no defined behaviour for
that, so if it works, it's by chance and might not work later).
To do what you want, I suggest you override the save method in the
model, and add the startdate from the related Project model to the
Role model.
I'm a bit rusty on this, but something like this should work:
def save(self):
if self.project != None:
self.rolestartdate = project.startdate
#don't worry about handling if self.project == None; foreign keys
are required by default and the superclass' save method will raise an
exception
super(Role, self).save()
2009/12/6 Guy <guyea...@gmail.com>:
>
> I am using the code shown below. The part causing the problem is the
> Role class which describes the role a person might have on a project.
> As part of that role, I would have an attribute that records the start
> and end date of the person's involvement. The problem seems to be
> coming when I make an ill-fated attempt to define a default start date
> as the startdate of the project to which the role is linked.
>
> ---------------------code------------------------------------------
> from django.db import models
>
> class Project(models.Model):
> """class to describe the attributes that characterize a project"""
>
> #reference number for project
> referencenum = models.CharField("reference number for project",
> max_length=20)
> #begin date of project
> startdate = models.DateField()
>
> class Role(models.Model):
> """class to describe a Person object's affiliation to a Project
> object"""
>
> #project in which person is involved
> project = models.ForeignKey(Project)
>
> #begin date of person's involvement on project; this is the
> problem line
> rolestartdate = models.DateField(default = \
> Project.objects.get
> (pk=project.id).startdate)
>
> -----------------------------------------------------------------
> when I run:
> manage.py syncdb
> I get the following error:
>
> rolestartdate = models.DateField(default = Project.objects.get
> (pk=project.id).st
> artdate)
> AttributeError: 'ForeignKey' object has no attribute 'id'
>
> I was under the impression that django creates an attribute on every
> model, foo.id, that serves as a primary key.
>
> Many thanks in advance to anyone who can explain what what I not
> grasping here.
>
> --
>
> You received this message because you are subscribed to the Google Groups
> "Django users" group.
> To post to this group, send email to django-us...@googlegroups.com.
> To unsubscribe from this group, send email to
> django-users+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/django-users?hl=en.
>
>
>
--
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-us...@googlegroups.com.
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en.
