How to create model allowing infinite submodels in django? - django

Question

Im creating a site where you can write down your goals, you should be able to split every goal into subgoals if chosen, and allow those subgoals to be split into subgoals infinitely.
This code below shows what i came up with first for the models, the first model is for creating a goal, the second model can either either be a subgoal of the goal or a subgoal of the subgoal.
But it seems like a really bad way to go around this problem.
Django semi-newbie BTW...
from django.db import models
from django.contrib.auth.models import User
class Goal(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE, default=None)
title = models.CharField(max_length=70, null=True)
content = models.TextField(blank=True)
slug = models.SlugField(max_length=50, editable=False)
date_created = models.DateTimeField(auto_now_add=True, null=True)
class Meta:
unique_together = ['user', 'title']
def __str__(self):
return self.user.username + " - " + self.title
def save(self, *args, **kwargs):
self.slug = self.title.replace(' ', '-').lower()
super(Goal, self).save(*args, **kwargs)
class SubGoal(models.Model):
goal = models.ForeignKey(
Goal, on_delete=models.CASCADE, null=True, blank=True)
parent = models.ForeignKey(
"SubGoal", on_delete=models.CASCADE, null=True, blank=True)
title = models.CharField(max_length=70)
content = models.TextField(blank=True)
date_created = models.DateTimeField(auto_now_add=True, null=True)
def __str__(self):
try:
return self.goal.title + " - " + self.title
except:
return self.parent.title + " - " + self.title

Answer 1

You can make a ForeignKey to self. If the ForeignKey is NULL, then that goal has no parent, otherwise it refers to the parent:
from django.db import models
from django.contrib.auth.models import User
from django.conf import settings
django.utils.text import slugify
class Goal(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
title = models.CharField(max_length=70)
content = models.TextField(blank=True)
slug = models.SlugField(max_length=50, editable=False)
date_created = models.DateTimeField(auto_now_add=True)
parent = models.ForeignKey(
'self',
on_delete=models.SET_NULL,
null=True,
default=None,
related_name='subgoals'
)
class Meta:
constraints = [
models.UniqueConstraint(fields=['user', 'title'], name='user_title')
]
def __str__(self):
if self.parent_id is None:
return '{}-{}'.format(self.user.username, self.title)
else:
return '{}-{}'.format(str(self.parent), self.title)
def save(self, *args, **kwargs):
self.slug = slugify(self.title)
super(Goal, self).save(*args, **kwargs)
Note: It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation.