Nested Models in Serializer django - django

Question

I cannot get the last measurement for each device based on the device's ID from the measurement. If someone can advise me on how to implement this?
Models
class Devices(models.Model):
deviceid = models.AutoField(db_column='deviceId', primary_key=True) # Field name made lowercase.
devicename = models.CharField(db_column='deviceName', unique=True, max_length=128) # Field name made lowercase
devicestatus = models.IntegerField(db_column='deviceStatus') # Field name made lowercase.
Class Meta:
managed = False
db_table = 'devices'
class Measurements(models.Model):
measurementid = models.AutoField(db_column='measurementId', primary_key=True) # Field name made lowercase.
deviceid = models.ForeignKey(Devices, models.DO_NOTHING, related_name="measurment_details", db_column='deviceId') # Field name made lowercase.
measurement = models.CharField(max_length=64, blank=True, null=True)
class Meta:
managed = False
get_latest_by = 'measurementtime'
db_table = 'measurements'
Serializer
class MeasurmentsSerializer(serializers.ModelSerializer):
class Meta:
model = Measurements
fields = ('measurementid','measurement')
class DeviceSerializer(serializers.ModelSerializer):
latestmeasurment = serializers.SerializerMethodField()
count = 0
def get_latestmeasurment(self, obj):
qs = Measurements.objects.using('###').last()
serializer = MeasurmentsSerializer(instance=qs, many=False)
self.count = 1 + self.count
print(self.count , serializer.data )
return serializer.data
class Meta:
model = Devices
fields = ("devicename", 'latestmeasurment')
Views
class RetrieveAllDevicesView(viewsets.ModelViewSet):
http_method_names = ['get']
permission_classes = [permissions.IsAuthenticated]
serializer_class = DeviceSerializer
queryset = Devices.objects.using('###')
In serializer, you can see the count for primitive debug:
1 {'measurementid': 2942080, 'measurement': '35.0'}
2 {'measurementid': 2942080, 'measurement': '35.0'}
3 {'measurementid': 2942080, 'measurement': '35.0'}
4 {'measurementid': 2942080, 'measurement': '35.0'}
5 {'measurementid': 2942080, 'measurement': '35.0'}
6 {'measurementid': 2942080, 'measurement': '35.0'}
7 {'measurementid': 2942080, 'measurement': '35.0'}
8 {'measurementid': 2942080, 'measurement': '35.0'}
9 {'measurementid': 2942080, 'measurement': '35.0'}
10 {'measurementid': 2942080, 'measurement': '35.0'}
Response in JSON from view:
enter image description here

Answer 1

def get_latestmeasurment(self, obj):
device_measurements = obj.measurment_details.all()
last_measurement = device_measurements.order_by('id').last()
serializer = MeasurmentsSerializer(last_measurement)
return serializer.data
you get all measurments for each device and after sorting it you'll get the last one as your last_measurment