FastAPI BaseModel字典结构定义及JSON请求适配问题求助

目标请求JSON结构 #

{
    "a": [
        {
            "text": "text",
            "language": "en",
            "entities": [
                { "d": "g" },
                { "e": "h" },
                { "f": "i" }
            ]
        },
        {
            "text": "another text",
            "language": "en",
            "entities": [
                { "d": "z" }
            ]
        }
    ],
    "b": [
        {
            "text": "more texts",
            "language": "en",
            "entities": [
                { "d": "r" },
                { "e": "t" },
                { "f": "z" }
            ]
        }
    ],
    "c": ["d", "e", "f"]
}

当前FastAPI端点代码 #

@app.post("/json")
def method(a: AModel, b: BModel, c: CModel):  # code

当前BaseModel定义 #

class Input(BaseModel):
    text: str = Field (
        title="A text", example= "text"
    )
    language: str = Field (
        default=None, title="A language string", max_length=2, example="en"
    )
    entities: Dict[str, str] = Field (
        default=None, title="xxx.", 
        example= [{"d": "x"}, {"f": "y"}]
    )
    class Config:
        orm_mode=True

class CModel (BaseModel):
    c: List[str] = Field (
        title="xxx.", example= ["d", "e", "f"]
    )

class BModel (BaseModel):
    b: List[Input] = Field (
        title="yyy."
    )

class AModel (BaseModel):
    a: List[Input] = Field (
        title="zzz."
    )

返回的错误信息 #

{
    "detail": [
        {
            "loc": [
                "body",
                "trainingdata"
            ],
            "msg": "value is not a valid dict",
            "type": "type_error.dict"
        },
        {
            "loc": [
                "body",
                "testingdata"
            ],
            "msg": "value is not a valid dict",
            "type": "type_error.dict"
        },
        {
            "loc": [
                "body",
                "entities"
            ],
            "msg": "value is not a valid dict",
            "type": "type_error.dict"
        }
    ]
}

问题分析与修正方案 #

核心问题 #

1. 端点参数解析错误：当前端点将a、b、c作为独立的BaseModel参数，FastAPI会默认期望这些参数是独立字典或表单数据，但实际请求体是包含三个字段的单一JSON对象，导致解析不匹配。
2. entities字段类型不匹配：原JSON中entities是字典数组（[{"d":"g"}, ...]），但模型中定义为Dict[str, str]（单一字典），类型完全不符。
3. 冗余模型定义：AModel、BModel、CModel都是仅包裹单个字段的模型，可合并到顶层模型简化结构。

修正后的代码 #

修正后的BaseModel定义

from pydantic import BaseModel, Field
from typing import List, Dict

class Input(BaseModel):
    text: str = Field(title="A text", example="text")
    language: str = Field(default=None, title="A language string", max_length=2, example="en")
    # 修改entities为字典数组，匹配JSON结构，支持任意键值对
    entities: List[Dict[str, str]] = Field(default=None, title="实体列表", example=[{"d": "x"}, {"f": "y"}])
    
    class Config:
        orm_mode = True

# 顶层模型，直接对应整个请求体的结构
class RequestBody(BaseModel):
    a: List[Input] = Field(title="zzz.")
    b: List[Input] = Field(title="yyy.")
    c: List[str] = Field(title="xxx.", example=["d", "e", "f"])

修正后的端点代码

@app.post("/json")
def method(request_body: RequestBody):
    # 通过request_body.a、request_body.b、request_body.c访问对应数据
    return {"received_data": request_body.dict()}

说明 #

• 顶层RequestBody模型直接映射整个请求体的JSON结构，让FastAPI正确解析单一JSON对象。
• Input中的entities改为List[Dict[str, str]]，既匹配JSON中的数组结构，又支持任意不确定的键值对，满足不能硬编码键的需求。
• 移除冗余的AModel、BModel、CModel，简化代码结构。

内容的提问来源于stack exchange，提问作者AnnemarieWittig