如何将Django Ninja错误转为可用于API响应的Schema？

问题描述 #

使用Django Ninja开发API时，配置路由响应类型时遇到报错，代码示例如下：

from ninja import Schema
from ninja.errors import HttpError, ValidationError

class MyOutSchema(Schema):
    # 省略Schema字段定义
    pass

@router.get("/", response={200: MyOutSchema, 404:XXX, 429:XXX, 400:XXX})
def my_api(request, params):
    # 可能抛出HttpError或ValidationError的业务代码
    pass

直接将HttpError或ValidationError作为响应类型时，生成接口文档会触发以下错误：

[14:13:01] [DJANGO] @router.get(
[14:13:01] [DJANGO]      ^^^^^^^^^^^
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/router.py", line 239, in decorator
[14:13:01] [DJANGO]     self.add_api_operation(
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/router.py", line 288, in add_api_operation
[14:13:01] [DJANGO]     path_view.add_operation(
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/operation.py", line 306, in add_operation
[14:13:01] [DJANGO]     operation = OperationClass(
[14:13:01] [DJANGO]                 ^^^^^^^^^^^^^^^
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/operation.py", line 75, in __init__
[14:13:01] [DJANGO]     self.response_models = self._create_response_model_multiple(response)
[14:13:01] [DJANGO]                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/operation.py", line 241, in _create_response_model_multiple
[14:13:01] [DJANGO]     result[code] = self._create_response_model(model)
[14:13:01] [DJANGO]                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/operation.py", line 248, in _create_response_model
[14:13:01] [DJANGO]     return type("NinjaResponseSchema", (Schema,), attrs)
[14:13:01] [DJANGO]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[14:13:01] [DJANGO]   File "/home/Work/web-framework/.venv/lib/python3.11/site-packages/ninja/schema.py", line 145, in __new__
[14:13:01] [DJANGO]     result = super().__new__(cls, name, bases, namespace, **kwargs)
[14:13:01] [DJANGO]              ^
[14:13:01] [DJANGO] ^
[14:13:01] [DJANGO] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[14:13:01] [DJANGO]   File "pydantic/main.py", line 197, in pydantic.main.ModelMetaclass.__new__
[14:13:01] [DJANGO]   File "pydantic/fields.py", line 506, in pydantic.fields.ModelField.infer
[14:13:01] [DJANGO]   File "pydantic/fields.py", line 436, in pydantic.fields.ModelField.__init__
[14:13:01] [DJANGO]   File "pydantic/fields.py", line 557, in pydantic.fields.ModelField.prepare
[14:13:01] [DJANGO]   File "pydantic/fields.py", line 831, in pydantic.fields.ModelField.populate_validators
[14:13:01] [DJANGO]   File "pydantic/validators.py", line 765, in find_validators
[14:13:01] [DJANGO] RuntimeError: no validator found for <class 'ninja.errors.ValidationError'>, see `arbitrary_types_allowed` in Config

尝试用None替代XXX也无效，需要解决如何将Ninja错误对象转为可Schema化的类，或正确配置错误响应类型。

解决方案 #

Django Ninja要求响应类型必须是继承自Schema的类，错误异常类不符合要求，可通过以下两种方式解决：

1. 自定义错误响应Schema #

针对不同错误类型创建匹配Ninja默认返回格式的Schema：

from ninja import Schema

# 通用错误Schema，对应HttpError返回格式
class ErrorSchema(Schema):
    detail: str

# 验证错误Schema，对应ValidationError返回格式
class ValidationErrorSchema(Schema):
    detail: list[dict[str, str]]

在路由中使用这些Schema：

@router.get("/", response={
    200: MyOutSchema,
    404: ErrorSchema,
    429: ErrorSchema,
    400: ValidationErrorSchema
})
def my_api(request, params):
    # 业务代码示例
    # raise HttpError(404, "资源不存在")
    # raise ValidationError({"name": "不能为空"})
    pass

2. 复用Ninja内置错误Schema（推荐） #

Django Ninja内部已定义好标准错误Schema，可直接导入使用：

from ninja.errors import ErrorSchema, ValidationErrorSchema

直接在路由中引用：

@router.get("/", response={
    200: MyOutSchema,
    404: ErrorSchema,
    429: ErrorSchema,
    400: ValidationErrorSchema
})
def my_api(request, params):
    # 业务代码
    pass

注：不同版本的Django Ninja可能调整内置Schema的命名或导入路径，若找不到则使用自定义方式。

问题根源 #

HttpError和ValidationError是异常类而非Schema类，Ninja生成OpenAPI文档时需要基于Schema解析响应结构，异常类无法被底层依赖的Pydantic识别为有效数据模型，因此会抛出找不到验证器的错误。

内容的提问来源于stack exchange，提问作者CrUncheSSH