Question

I have a question about a ForeignKey reference problem with django.

This is a part of my code :

App ticketsTrader

class TicketsTrader(models.Model):
    seller = models.ForeignKey(User, related_name='ticketsTrader_seller')
    buyer = models.ForeignKey(User, related_name='ticketsTrader_buyer')
    inscription = models.ForeignKey(Inscription)
    transactionCode = models.CharField(max_length=30,blank=False,null=False)
    ...

App inscription

class Event(models.Model):
    title = models.CharField(max_length=75)
    description = models.TextField()
    ...

class Inscription(models.Model):
    event = models.ForeignKey(Event)
    packs = models.ManyToManyField(PackChoise)
    user = models.ForeignKey(User)
    ...

    def __unicode__(self):
        return self.event.__unicode__() + u': ' + self.user.__unicode__()

    def inscriptionKey(self):
        return str(self.pk) + '_' + str(self.valkey)

But when I try to acces to the “Add Ticket Trader” interface in my Grapelli admin, I get an error message :

User matching query does not exist.

Python27\lib\site-packages\django\db\models\query.py in get, line 366

In template \grappelli\templates\admin\includes\fieldset.html, error
at line 19

What I want to get is : in the “inscription” column of my ticketTrader table get the value of the unique id (pk) of my “Inscription” table.

Or the value of the “inscriptionKey” but I don’t think it’s possible.

Django Version:1.4 / Python Version: 2.7.3 / South last version

Thanks for your help 🙂

Answer 1

I can only guess:

TicketsTrader has a foreign key to Inscription, which has a foreign key to User and uses that key in its __unicode__() method.

Now, I don’t know Grapelli but the default admin app would render a dropdown for Inscription-s on the Add TicketsTrader page. If some of the Inscription-s pointed to non-existing User-s, then their __unicode__() method would fail with the error message you specified.

The question is how could some User-s be missing and Inscription-s pointing to them not. Well, if you use e.g. MySQL+MyISAM, foreign keys are not enforced there so all sorts of weird things can happen.