Add a hook to intercept ValidationError

README.rst

@@ -310,6 +310,26 @@ Open Api Specification.
             self.request.app["model"].remove_pet(id)
             return web.Response(status=204)
 
+
+Custom Validation error
+-----------------------
+
+You can redefine the on_validation_error hook in your PydanticView
+
+.. code-block:: python3
+
+    class PetView(PydanticView):
+
+        async def on_validation_error(self,
+                                      exception: ValidationError,
+                                      context: str):
+            errors = exception.errors()
+            for error in errors:
+                error["in"] = context  # context is "body", "headers", "path" or "query string"
+                error["custom"] = "your custom field ..."
+            return json_response(data=errors, status=400)
+
+
 Demo
 ----
 

aiohttp_pydantic/injectors.py

@@ -2,7 +2,7 @@ import abc
 import typing
 from inspect import signature
 from json.decoder import JSONDecodeError
-from typing import Callable, Tuple
+from typing import Callable, Tuple, Literal
 
 from aiohttp.web_exceptions import HTTPBadRequest
 from aiohttp.web_request import BaseRequest
@@ -12,6 +12,9 @@ from pydantic import BaseModel
 from .utils import is_pydantic_base_model
 
 
+CONTEXT = Literal["body", "headers", "path", "query string"]
+
+
 class AbstractInjector(metaclass=abc.ABCMeta):
     """
     An injector parse HTTP request and inject params to the view.
@@ -19,7 +22,7 @@ class AbstractInjector(metaclass=abc.ABCMeta):
 
     @property
     @abc.abstractmethod
-    def context(self) -> str:
+    def context(self) -> CONTEXT:
         """
         The name of part of parsed request
         i.e "HTTP header", "URL path", ...

aiohttp_pydantic/view.py

@@ -1,6 +1,6 @@
 from functools import update_wrapper
 from inspect import iscoroutinefunction
-from typing import Any, Callable, Generator, Iterable, Set, ClassVar
+from typing import Any, Callable, Generator, Iterable, Set, ClassVar, Literal
 import warnings
 
 from aiohttp.abc import AbstractView
@@ -17,6 +17,7 @@ from .injectors import (
     MatchInfoGetter,
     QueryGetter,
     _parse_func_signature,
+    CONTEXT,
 )
 
 
@@ -88,6 +89,22 @@ class PydanticView(AbstractView):
             injectors.append(HeadersGetter(header_args, default_value(header_args)))
         return injectors
 
+    async def on_validation_error(
+        self, exception: ValidationError, context: CONTEXT
+    ) -> StreamResponse:
+        """
+        This method is a hook to intercept ValidationError.
+
+        This hook can be redefined to return a custom HTTP response error.
+        The exception is a pydantic.ValidationError and the context is "body",
+        "headers", "path" or "query string"
+        """
+        errors = exception.errors()
+        for error in errors:
+            error["in"] = context
+
+        return json_response(data=errors, status=400)
+
 
 def inject_params(
     handler, parse_func_signature: Callable[[Callable], Iterable[AbstractInjector]]
@@ -109,11 +126,7 @@ def inject_params(
                 else:
                     injector.inject(self.request, args, kwargs)
             except ValidationError as error:
-                errors = error.errors()
-                for error in errors:
-                    error["in"] = injector.context
-
-                return json_response(data=errors, status=400)
+                return await self.on_validation_error(error, injector.context)
 
         return await handler(self, *args, **kwargs)
 

tests/test_hook_to_custom_response.py

@@ -0,0 +1,56 @@
+from typing import Iterator, List, Optional
+
+from aiohttp import web
+from aiohttp.web_response import json_response
+from pydantic import BaseModel
+
+from aiohttp_pydantic import PydanticView
+
+
+class ArticleModel(BaseModel):
+    name: str
+    nb_page: Optional[int]
+
+
+class ArticleModels(BaseModel):
+    __root__: List[ArticleModel]
+
+    def __iter__(self) -> Iterator[ArticleModel]:
+        return iter(self.__root__)
+
+
+class ArticleView(PydanticView):
+
+    async def post(self, article: ArticleModel):
+        return web.json_response(article.dict())
+
+    async def put(self, articles: ArticleModels):
+        return web.json_response([article.dict() for article in articles])
+
+    async def on_validation_error(self, exception, context):
+        errors = exception.errors()
+        for error in errors:
+            error["in"] = context
+            error["custom"] = "custom"
+        return json_response(data=errors, status=400)
+
+
+async def test_post_an_article_with_wrong_type_field_should_return_an_error_message(
+    aiohttp_client, loop
+):
+    app = web.Application()
+    app.router.add_view("/article", ArticleView)
+
+    client = await aiohttp_client(app)
+    resp = await client.post("/article", json={"name": "foo", "nb_page": "foo"})
+    assert resp.status == 400
+    assert resp.content_type == "application/json"
+    assert await resp.json() == [
+        {
+            "in": "body",
+            "loc": ["nb_page"],
+            "msg": "value is not a valid integer",
+            "custom": "custom",
+            "type": "type_error.integer",
+        }
+    ]