error message with i18n support in FastAPI

response example

{
  "errors": [
    {
      "loc": [
        "body",
        "string"
      ],
      "msg": "確保此值最多有 10 個字符",
      "type": "value_error.any_str.max_length",
      "ctx": {
        "limit_value": 10
      }
    },
    {
      "loc": [
        "body",
        "nested",
        "body"
      ],
      "msg": "確保此值最多有 2 個字符",
      "type": "value_error.any_str.max_length",
      "ctx": {
        "limit_value": 2
      }
    },
    {
      "loc": [
        "body",
        "nested",
        "inner",
        "inner_body"
      ],
      "msg": "確保此值最多包含 2 個項目",
      "type": "value_error.list.max_items",
      "ctx": {
        "limit_value": 2
      }
    },
    {
      "loc": [
        "body",
        "nested",
        "inner",
        "cat"
      ],
      "msg": "鑑別器 'color' 和值 'ccc' 不匹配（允許的值: 'black', 'white'）",
      "type": "value_error.discriminated_union.invalid_discriminator",
      "ctx": {
        "discriminator_key": "color",
        "discriminator_value": "ccc",
        "allowed_values": "'black', 'white'"
      }
    }
  ]
}

parameters

all parameters are optional

param	description	default
locale_path	the path of your locale files	locales
locale_list	support locales in your app in tuple	('zh-TW', 'ja-JP', 'en-US')
bind_to_life_span	set to True if you want the translator instance be created when on app startup	False

Attention

• For FastAPI >=0.100.0 and pydantic v2, please use ^0.4.0
• For FastAPI < 0.100.0 nad pydantic v1, please use ^0.3.0
• built-in locales are zh-TW, en-US, ja-JP, you can change the locales by yourself

How to run

• use setup

from fastapi_validation_i18n import setup
from fastapi import FastAPI
app = FastAPI()
setup(app, locale_path=..., locale_list=...)

• use middleware and exception handler

from fastapi import FastAPI
from fastapi_validation_i18n import I18nMiddleware, i18n_exception_handler
from fastapi.exceptions import RequestValidationError

app = FastAPI()

app.add_middleware(I18nMiddleware, locale_path='your-publish-path')

app.add_exception_handler(
    RequestValidationError,
    i18n_exception_handler
)

Other

• publish locales to your app path

# default to "locale" in your project path
poetry run publish-locale <your-path> [--locale]

• how to set locale

there are 3 ways to set locale

1. set accept-language header to your request
2. set an API with locale in path
3. set locale query parameter to your request

you can see the example for more detail