Django nested serializer giving me None for all fields - django

Question

So I'm working with Django and djangorestframework (versions 3.2.12 and 3.12.4, respectively) and I'm running into an issue with nested serializers.
I've got FantasyLeague and FantasyLeagueSettings models. FantasyLeagueSettings has a FK to FantasyLeague
models.py
class FantasyLeague(models.Model):
name = models.CharField(max_length=100)
managers = models.ManyToManyField(User)
yahoo_league_id = models.CharField(max_length=20, blank=True, null=True)
class FantasyLeagueSettings(models.Model):
league = models.ForeignKey(FantasyLeague, on_delete=models.CASCADE, related_name='settings')
max_teams = models.IntegerField(blank=True, null=True)
num_playoff_teams = models.IntegerField(blank=True, null=True)
playoff_start_week = models.IntegerField(blank=True, null=True)
I'm serializing them like so:
serializers.py
class FantasyLeagueSettingsSerializer(serializers.ModelSerializer):
class Meta:
model = FantasyLeagueSettings
fields = ['max_teams', 'num_playoff_teams', 'playoff_start_week']
class FantasyLeagueSerializer(serializers.ModelSerializer):
managers = UserSerializer(read_only=True, many=True)
settings = FantasyLeagueSettingsSerializer(many=False, read_only=True)
class Meta:
model = FantasyLeague
fields = ['id', 'name', 'managers', 'settings', 'yahoo_league_id' ]
But for some reason FantasyLeagueSerializer(league).data gives me a value of None for all of the settings fields (even though the settings data exists)
Testing code:
league = FantasyLeague.objects.get(pk=1)
print('🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥')
print(FantasyLeagueSerializer(league).data)
# FantasyLeagueSerializer(league).data: {'id': 1, 'name': 'PLAYING FOR KEEPS', 'managers': [OrderedDict([('id', 1), ('username', 'Smurflo'), ('settings', OrderedDict([('selected_theme', 'kanagawa')])), ('is_staff', True)])], 'settings': OrderedDict([('max_teams', None), ('num_playoff_teams', None), ('playoff_start_week', None)]), 'yahoo_league_id': '461051' }
# Note how all of the settings fields are None
# Even though league.settings clearly has data and FantasyLeagueSettingsSerializer works
print('🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆🎆')
print(FantasyLeagueSettingsSerializer(league.settings.all()[0]).data)
# {'max_teams': 12, 'num_playoff_teams': 6, 'playoff_start_week': 15}
Anyone know what's going on here? What am I missing?

Answer 1

The reason for the problem is due to the uncoordinated relationship between FantasyLeague and FantasyLeagueSettings.
if instances of FantasyLeague can have more than one settings, then you should change many=False to many=True in settings field of FantasyLeagueSerializer serializer.
class FantasyLeagueSerializer(serializers.ModelSerializer):
...
settings = FantasyLeagueSettingsSerializer(many=True, read_only=True)
...
but if FantasyLeague's instances can have at most one settings, then you should change league's type to OneToOneField in FantasyLeagueSettings model.
class FantasyLeagueSettings(models.Model):
league = models.OneToOneField(FantasyLeague, on_delete=models.CASCADE, related_name='settings')
...