count livestocks by type & set in herd model by signals

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)