Django : ManyToMany, Who is the most efficient? - django

Question

I hesitate between two conceptions of my models.
In my website, there are football teams. These teams contains coachs, players, directors... etc.
Currently, I modeled this like that (1) :
class Team(models.Model):
name = models.CharField(max_length=25,primary_key=True)
class Chief(models.Model):
created_at = models.DateField(auto_now_add=True)
team = models.ForeignKey(Team, null=False,on_delete=models.CASCADE)
user = models.ForeignKey(User, null=False,on_delete=models.CASCADE)
class Player(models.Model):
created_at = models.DateField(auto_now_add=True)
team = models.ForeignKey(Team, null=False,on_delete=models.CASCADE)
user = models.ForeignKey(User, null=False,on_delete=models.CASCADE)
position = models.CharField(max_length=30) #3 positions posible
class Director(models.Model):
created_at = models.DateField(auto_now_add=True)
team = models.ForeignKey(Team, null=False,on_delete=models.CASCADE)
user = models.ForeignKey(User, null=False,on_delete=models.CASCADE)
The problem is when I want to get all members of a team (chiefs, directors and players), I have to execute 3 requests.
But the advantage is when I want just all directors, I just search in Director entity !
I hesitate to delete these 3 models (Director, Player and Chief) and make 3 relations ManyToMany in Team like that (2) :
class Team(models.Model):
name = models.CharField(max_length=25,primary_key=True)
chiefs = models.ManyToManyField(User)
directors = models.ManyToManyField(User)
players_position1 = models.ManyToManyField(User)
players_position2 = models.ManyToManyField(User)
players_position3 = models.ManyToManyField(User)
Which is the most efficient way between the (1) and the (2) ?

Answer 1

You can use model inheritance
models.py
class TeamMember(models.Model):
created_at = models.DateField(auto_now_add=True)
team = models.ForeignKey(Team, null=False,on_delete=models.CASCADE)
user = models.ForeignKey(User, null=False,on_delete=models.CASCADE)
class Chief(TeamMember):
pass
class Director(TeamMember):
pass
class Player(TeamMember):
position = models.CharField(max_length=30)
views.py
#Get all members
members = TeamMember.objects.all()
#Only players
players = Player.objects.all()

Answer 2

class Team(models.Model):
name = models.CharField(max_length=25,primary_key=True)
class MemberQuerySet(models.QuerySet):
def chiefs(self):
return self.filter(position='a')
def directors(self):
return self.filter(position='b')
def players(self):
return self.filter(position__in=['c', 'd', 'e'])
class Member(models.Model):
created_at = models.DateField(auto_now_add=True)
team = models.ForeignKey(Team, models.CASCADE, related_name="members")
user = models.ForeignKey(User, models.CASCADE)
position = models.CharField(max_length=1, choices=(
('a', 'chief'),
('b', 'director'),
('c', 'player position 1'),
('d', 'player position 2'),
('e', 'player position 3'))
objects = MemberQuerySet.as_manager()
Now you can get all members of a team or just the players with just one hit on the database
members = Team.objects.get(pk='someteam').members
players = Team.objects.get(pk='someteam').members.players()