Many to Many in two directions - django

Question

I have a friend that requested something that I was thinking would be simple and quick. It never turns out that way. Quick disclaimer, model design is a krux of mine. I often spend too long perfecting it only to have to rework it several times. Anyway, here is the current state of my model. For everything, it works, except when creating 'raids'.
from django.db import models
# Create your models here.
class PlayerRole(models.Model):
"""
PlayerRole Model
"""
role = models.CharField(max_length=20)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return self.role
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['role']
class PlayerClass(models.Model):
"""
PlayerClass Model
"""
name = models.CharField(max_length=100)
color = models.CharField(max_length=6)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return self.name
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['name']
class Player(models.Model):
"""
Player Model
"""
name = models.CharField(max_length=100)
playerclass = models.ForeignKey(PlayerClass, on_delete=models.CASCADE, blank=True, null=True)
playerrole = models.ForeignKey(PlayerRole, on_delete=models.CASCADE, blank=True, null=True)
value = models.IntegerField(default=0)
reliability = models.IntegerField(default=0)
last_drop = models.DateField(auto_now=False, blank=True, null=True)
last_raid_attended = models.DateField(auto_now=False, blank=True, null=True)
last_boss_attended = models.DateField(auto_now=False, blank=True, null=True)
drop_received = models.BooleanField(default=False)
note = models.TextField(null=True, blank=True)
core_raider = models.BooleanField(default=False)
enabled = models.BooleanField(default=True)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return self.name
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['name']
class WoWInstance(models.Model):
"""
Instance Model
"""
name = models.CharField(max_length=100)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return self.name
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['name']
class Boss(models.Model):
"""
Boss Model
"""
name = models.CharField(max_length=100)
instance = models.ForeignKey(WoWInstance, on_delete=models.CASCADE)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return self.name
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['name']
class Raid(models.Model):
"""
Raid Model
"""
date = models.DateTimeField(auto_now_add=True)
boss = models.ForeignKey(Boss, on_delete=models.CASCADE, null=True, blank=True)
success = models.BooleanField()
attendees = models.ManyToManyField(Player)
# this function will be invoked when this model object is foreign key of other model(for example Employee model.).
def __str__(self):
return str(self.date) + ' + ' + self.boss.name
# this is a inner class which is used to define unique index columns. You can specify multiple columns in a list or tuple.
class Meta:
unique_together = ['boss']
The idea here is simply to track attendance on each attempt at fighting something in a game. In the most general and simple sense - Many Raids can contain many of the same Bosses. Many Raids can contain many of the same Players.
Now, I thought that because Django automatically creates ID fields, this method wouldn't be an issue. But, it seems not to be the case. If I create a raid with the same Boss more than once, I get...
Raid with this Boss already exists.
What am I missing here? Since all Raid and Boss are unique, shouldn't the two never overlap?

Answer 1

If I create a raid with the same Boss more than once, I get...
Raid with this Boss already exists.
Well that is due to the unique_together constraint:
class Raid(models.Model):
# ...
class Meta:
unique_together = ['boss']
If you write unique_together, it means you enforce a uniqness constraint on a combination of fields. But since you here have mentioned only one field ('boss'), you thus add a unique=True constraint on that specific field.
It thus means that no two Raids can exist with the same boss field. You probably want to remove that.
Since all Raid and Boss are unique, shouldn't the two never overlap?
The Raids and Bosses are already unique. An object does not belong to two models at once (unless one is the subclass of another, but let us ignore that case). You even made the name unique as well (although you better do that by adding a unique=True parameter to the name fields). So there is no need at all to make the 'boss' unique here, since you clearly do not want that.