Abstract DRF serializer validation

- Subclass InvenTree.InvenTreeModelSerializer
- Ensures model data is checked too (after serializer checks are performed)

InvenTree/InvenTree/serializers.py

@@ -2,7 +2,6 @@
 from __future__ import unicode_literals
 
 from rest_framework import serializers
-from rest_framework import generics
 
 from django.contrib.auth.models import User
 
@@ -22,3 +21,20 @@ class UserSerializerBrief(serializers.ModelSerializer):
             'pk',
             'username',
         ]
+
+
+class InvenTreeModelSerializer(serializers.ModelSerializer):
+    """
+    Inherits the standard Django ModelSerializer class,
+    but also ensures that the underlying model class data are checked on validation.
+    """
+
+    def validate(self, data):
+        # Run any native validation checks first (may throw an ValidationError)
+        data = super(serializers.ModelSerializer, self).validate(data)
+
+        # Now ensure the underlying model is correct
+        instance = self.Meta.model(**data)
+        instance.clean()
+
+        return data