news unique slug creation

apps/news/serializers.py

@@ -177,6 +177,12 @@ class NewsBackOfficeBaseSerializer(NewsBaseSerializer):
             'backoffice_title': {'allow_null': False},
         }
 
+    def validate(self, attrs):
+        slugs = attrs.get('slugs', {})
+        if models.News.objects.filter(slugs__values__contains=[slugs.values()]).exists():
+            raise serializers.ValidationError({'slugs': _('News with this slug already exists.')})
+        return attrs
+
 
 class NewsBackOfficeDetailSerializer(NewsBackOfficeBaseSerializer,
                                      NewsDetailSerializer):