count livestocks by type & set in herd model by signals

apps/herd/exception.py

@@ -5,3 +5,8 @@ from rest_framework import status
 class UniqueRancherApiException(APIException):
     status_code = status.HTTP_403_FORBIDDEN
     default_detail = "دامدار با این کد ملی از قبل در سیستم وجود دارد"  # noqa
+
+
+class HerdCapacityException(APIException):
+    status_code = status.HTTP_403_FORBIDDEN
+    default_detail = "مقدار حجم سبک و سنگین وارد شده از ظرفیت گله بیشتر میباشد"  # noqa

apps/herd/web/api/v1/serializers.py

@@ -4,8 +4,9 @@ from apps.authentication.api.v1.serializers.serializer import (
     ProvinceSerializer,
     CitySerializer
 )
-from rest_framework import serializers
+from apps.herd.exception import HerdCapacityException
 from apps.herd.models import Herd, Rancher
+from rest_framework import serializers
 
 
 class HerdSerializer(serializers.ModelSerializer):
@@ -14,6 +15,14 @@ class HerdSerializer(serializers.ModelSerializer):
         model = Herd
         fields = '__all__'
 
+    def validate(self, attrs):
+        """ some validations for herd """
+
+        if attrs['heavy_livestock_number'] + attrs['light_livestock_number'] > attrs['capacity']:
+            raise HerdCapacityException()
+
+        return attrs
+
     def to_representation(self, instance):
         """ Customize serializer output """
         representation = super().to_representation(instance)

apps/livestock/apps.py

@@ -4,3 +4,6 @@ from django.apps import AppConfig
 class LivestockConfig(AppConfig):
     default_auto_field = 'django.db.models.BigAutoField'
     name = 'apps.livestock'
+
+    def ready(self):
+        import apps.livestock.signals

apps/livestock/signals.py

@@ -0,0 +1,31 @@
+from django.db.models.signals import post_save, post_delete
+from django.dispatch import receiver
+from django.db.models import Sum, Count, Q
+from .models import LiveStock
+
+
+def update_herd_statistics(instance: LiveStock):
+    """
+    update light & heavy livestock number in rancher herd
+    """
+    counts = LiveStock.objects.filter(
+        herd__rancher=instance.herd.rancher,
+        herd=instance.herd
+    ).aggregate(
+        light_livestock_number=Count('id', filter=Q(weight_type='L')),
+        heavy_livestock_number=Count('id', filter=Q(weight_type='H'))
+    )
+
+    instance.herd.light_livestock_number = counts['light_livestock_number']
+    instance.herd.heavy_livestock_number = counts['heavy_livestock_number']
+    instance.herd.save(update_fields=['light_livestock_number', 'heavy_livestock_number'])
+
+
+@receiver(post_save, sender=LiveStock)
+def update_herd_on_livestock_save(sender, instance, **kwargs):
+    update_herd_statistics(instance)
+
+
+@receiver(post_delete, sender=LiveStock)
+def update_herd_on_livestock_delete(sender, instance, **kwargs):
+    update_herd_statistics(instance)