From 5105e53b7aab31b6ab20b220883fe622bc62c2de Mon Sep 17 00:00:00 2001
From: Radoslav Georgiev <radorado@hacksoft.io>
Date: Fri, 28 Dec 2018 19:24:43 +0200
Subject: [PATCH] Move code samples to `utils.py`

---
 README.md |  2 ++
 utils.py  | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/README.md b/README.md
index a2ba52e..9859da5 100644
--- a/README.md
+++ b/README.md
@@ -349,6 +349,8 @@ class CourseCreateApi(
         return Response(status=status.HTTP_201_CREATED)
 ```
 
+All of code above can be found in `utils.py` in this repository.
+
 ## Inspiration
 
 The way we do Django is inspired by the following things:
diff --git a/utils.py b/utils.py
index 36c1f6c..a750fc5 100644
--- a/utils.py
+++ b/utils.py
@@ -1,3 +1,9 @@
+from rest_framework import serializers
+from rest_framework import exceptions as rest_exceptions
+
+from django.core.exceptions import ValidationError
+
+
 def create_serializer_class(name, fields):
     return type(name, (serializers.Serializer, ), fields)
 
@@ -9,3 +15,46 @@ def inline_serializer(*, fields, data=None, **kwargs):
         return serializer_class(data=data, **kwargs)
 
     return serializer_class(**kwargs)
+
+
+def get_first_matching_attr(obj, *attrs, default=None):
+    for attr in attrs:
+        if hasattr(obj, attr):
+            return getattr(obj, attr)
+
+    return default
+
+
+def get_error_message(exc):
+    if hasattr(exc, 'message_dict'):
+        return exc.message_dict
+    error_msg = get_first_matching_attr(exc, 'message', 'messages')
+
+    if isinstance(error_msg, list):
+        error_msg = ', '.join(error_msg)
+
+    if error_msg is None:
+        error_msg = str(exc)
+
+    return error_msg
+
+
+class ExceptionHandlerMixin:
+    """
+    Mixin that transforms Django and Python exceptions into rest_framework ones.
+    without the mixin, they return 500 status code which is not desired.
+    """
+    expected_exceptions = {
+        ValueError: rest_exceptions.ValidationError,
+        ValidationError: rest_exceptions.ValidationError,
+        PermissionError: rest_exceptions.PermissionDenied
+    }
+
+    def handle_exception(self, exc):
+        if isinstance(exc, tuple(self.expected_exceptions.keys())):
+            drf_exception_class = self.expected_exceptions[exc.__class__]
+            drf_exception = drf_exception_class(get_error_message(exc))
+
+            return super().handle_exception(drf_exception)
+
+        return super().handle_exception(exc)