Django - Foreign Key default

Question

I have problem with setting default value for my ForeignKey field in model. Here is my code: ``` class Group(models.Model): name = models.CharField(max_length=50) event = models.ForeignKey(Event) def __str__(self): return self.name class Slot(models.Model): title = models.CharField(max_length=50, blank = True) name = models.ForeignKey(SlotName) is_taken = models.BooleanField(default=False) usr = models.ForeignKey('auth.User', blank=True, null=True) group = models.ForeignKey(Group) event = models.ForeignKey(Event) #i would like to have something like "default=group.event" here def __str__(self): return self.name.name ``` This is a simple calendar app, and the idea is that i have an event that people can sign up for in specified groups. So I would like to be able to create event and at the same time create some groups, and then add slots to groups. I have event field in Slot model because I need to make sure that people won't be able to sign up for 2 slots at the same time, and I also n…

Accepted Answer

I had a similar problem trying to add a foreign key to a migration without a default value. Remove the lambda expression and let the default value as nullable (None) and try again with the following code sample. It worked perfectly for me.

e.g:

```
from django.db import models

class Slot(models.Model):                                                       
    event = models.ForeignKey('Event', null=True)                               
    group = models.ForeignKey('Group', null=True)                               
    def save(self, *args, **kwargs):                                            
        if(self.group is not None and self.group.event is not None):            
            self.event = self.group.event                                       
        super(Slot, self).save(*args, **kwargs)

class Event(models.Model):                                                      
    name = models.CharField(max_length=100)

class Group(models.Model):                                                      
    name  = models.CharField(max_length=100)                                    
    event = models.ForeignKey('Event')  
```

I omitted the non interesting fields on models for the sake of simplicity. I hope it could help you.

Django - Foreign Key default

Solution

Problem