python type_error ai_generated true

pydantic.error_wrappers.ValidationError: 1 validation error for Item response -> name str type expected (type=type_error.str)

ID: python/fastapi-response-model-serialization-error

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2025-07-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.9 active — — —
3.10 active — — —

Root Cause

FastAPI 路径操作返回的数据类型与响应模型不匹配

generic

中文

FastAPI 路径操作返回的数据类型与响应模型不匹配

Workarounds

  1. 95% success 确保返回数据与模型一致 
    class Item(BaseModel):
    name: str
@app.get('/item', response_model=Item)
def get():
    return Item(name='test')
  2. 90% success 使用 response_model_exclude_unset 
    @app.get('/item', response_model=Item, response_model_exclude_unset=True)
def get():
    return {'name': 'test'}

Dead Ends

Common approaches that don't work:

  1. 禁用响应模型验证 70% fail

    失去了类型安全性

  2. 返回原始字典而不使用模型 60% fail

    文档生成可能出错