[feature] Allow excluding fields from validation in ValidatedModelSerializer

Also handled exclusion of direct setting of m2m fields.

Author: nemesifier

openwisp_utils/api/serializers.py

@@ -1,4 +1,5 @@
 from django.core.exceptions import ImproperlyConfigured
+from django.db import models
 
 try:
     from rest_framework import serializers
@@ -10,7 +11,23 @@
 
 
 class ValidatedModelSerializer(serializers.ModelSerializer):
+    exclude_validation = None
+
     def validate(self, data):
-        instance = self.instance or self.Meta.model(**data)
-        instance.full_clean()
+        """Performs model validation on serialized data.
+
+        Allows to avoid having to duplicate
+        model validation logic in the REST API."""
+        instance = self.instance
+        # if instance is empty (eg: creation)
+        # simulate for validation purposes
+        if not instance:
+            Model = self.Meta.model
+            instance = Model()
+            for key, value in data.items():
+                # avoid direct assignment for m2m (not allowed)
+                if not isinstance(Model._meta.get_field(key), models.ManyToManyField):
+                    setattr(instance, key, value)
+        # perform model validation
+        instance.full_clean(exclude=self.exclude_validation)
         return data