Add exception handler for validation errors

todo/exceptions/exception_handler.py

@@ -0,0 +1,36 @@
+from typing import List
+from rest_framework.exceptions import ValidationError
+from rest_framework.response import Response
+from rest_framework import status
+from rest_framework.views import exception_handler
+from rest_framework.utils.serializer_helpers import ReturnDict
+
+from todo.dto.responses.error_response import ApiErrorDetail, ApiErrorResponse, ApiErrorSource
+
+
+def handle_exception(exc, context):
+    if isinstance(exc, ValidationError):
+        return Response(
+            ApiErrorResponse(
+                statusCode=status.HTTP_400_BAD_REQUEST,
+                message="Invalid request",
+                errors=format_validation_errors(exc.detail),
+            ).model_dump(mode="json", exclude_none=True),
+            status=status.HTTP_400_BAD_REQUEST,
+        )
+    return exception_handler(exc, context)
+
+
+def format_validation_errors(errors) -> List[ApiErrorDetail]:
+    formatted_errors = []
+    if isinstance(errors, ReturnDict | dict):
+        for field, messages in errors.items():
+            if isinstance(messages, list):
+                for message in messages:
+                    formatted_errors.append(ApiErrorDetail(detail=message, source={ApiErrorSource.PARAMETER: field}))
+            elif isinstance(messages, dict):
+                nested_errors = format_validation_errors(messages)
+                formatted_errors.extend(nested_errors)
+            else:
+                formatted_errors.append(ApiErrorDetail(detail=messages, source={ApiErrorSource.PARAMETER: field}))
+    return formatted_errors

todo_project/settings/base.py

@@ -49,4 +49,5 @@
         "rest_framework.renderers.JSONRenderer",
     ],
     "UNAUTHENTICATED_USER": None,
+    "EXCEPTION_HANDLER": "todo.exceptions.exception_handler.handle_exception",
 }