How to Implement One to Many in DRF - django-models

Question

I am Designing a Model
class Timer(models.Model):
total_time = models.FloatField(default=5)
date_time = models.DateTimeField(auto_now_add=True)
class WatchTiming(models.Model):
user = models.OneToOneField("authentication.User", on_delete=models.CASCADE, primary_key=True)
current_timer = models.ForeignKey(Timer, on_delete=models.CASCADE, related_name="current_timer")
previous_timers = models.ForeignKey(Timer, on_delete=models.CASCADE, related_name="previous_timers")
and serializer for this model is
from rest_framework import serializers
from .models import Timer, WatchTiming
class TimerSerializer(serializers.ModelSerializer):
class Meta:
model = Timer
exclude = ("id",)
class WatchTimingSerializer(serializers.ModelSerializer):
current_timer = TimerSerializer(required=False)
previous_timers = TimerSerializer(many=True, read_only=True)
user = serializers.PrimaryKeyRelatedField(read_only=True)
class Meta:
model = WatchTiming
fields = "__all__"
def create(self, validated_data):
watch_timing = WatchTiming.objects.create(user=self.context["request"].user, current_timer=Timer.objects.create())
return watch_timing
WatchTiming is a table that is used to store user watch time
current_timer stores today's timer
when the day expires current_timer values are added in the previous_timer and the current_timer value is replaced with the default
Now My issue is how can I create one to many relationships, I already have written relationships but its not working
I have been stuck on this for 4 consecutive days.

Answer 1

You can use a subserializer, just like you did with your TimerSerializers:
from rest_framework import serializers
from .models import Timer, WatchTiming
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User # authentication.User
fields = (
'id',
'username',
)
class WatchTimingSerializer(serializers.ModelSerializer):
current_timer = TimerSerializer(required=False)
previous_timers = TimerSerializer(read_only=True)
user = serializers.UserSerializer(read_only=True)
class Meta:
model = WatchTiming
fields = '__all__'
def create(self, validated_data):
return WatchTiming.objects.create(
user=self.context['request'].user,
current_timer=Timer.objects.create(),
)
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.
Note: The related_name=… parameter [Django-doc]
is the name of the relation in reverse, so from the Timer model to the WatchTiming
model in this case. Therefore it (often) makes not much sense to name it the
same as the forward relation. You thus might want to consider renaming the current_timer relation to watch_timings.

Answer 2

By using SerializerMethodField you can create one to many relationships.
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User
fields = "__all__"
class WatchTimingSerializer(serializers.ModelSerializer):
current_timer = TimerSerializer(required=False)
previous_timers = TimerSerializer(many=True, read_only=True)
user = serializers.SerializerMethodField(read_only=True)
class Meta:
model = WatchTiming
fields = "__all__"
def get_user(self, obj):
data = User.objects.filter(id=obj.id)
return UserSerializer(data, many=True).data