Pydantic：导出具有不同编码的相同类型的字段

Question

假设我有一个包含各种 timedelta 字段的模型，但我希望它们在导出到 JSON 时分别以不同的格式表示。我知道我可以为 timedelta 指定 JSON 编码器，但这适用于该类型的所有字段。有没有办法为给定字段指定 JSON 编码器？还是有其他方法可以做到这一点？

这里有一些代码作为例子：

from datetime import datetime, timedelta
from pydantic import BaseModel
from pydantic.json import timedelta_isoformat


class Example(BaseModel):
    delta_iso: timedelta # export using timedelta_isoformat
    delta_seconds_int: timedelta # export as int in seconds
    delta_seconds_float: timedelta # export as float in seconds
    delta_milliseconds_int: timedelta # export as int in milliseconds

    class Config:
        # This won't work because it applies to all fields above
        json_encoders = {
            timedelta: timedelta_isoformat,
        }

Answer 1

您可以提供自定义 json_dumps 函数。像这样：

import json
from datetime import datetime, timedelta
from pydantic import BaseModel
from pydantic.json import timedelta_isoformat


def custom_dumps(v, *, default):
    for key, value in v.items():
        if key == "delta_iso":
            v[key] = timedelta_isoformat(value)
        elif key == "delta_seconds_int":
            v[key] = int(value.total_seconds())
        elif key == "delta_seconds_float":
            v[key] = value.total_seconds()
        elif key == "delta_milliseconds_int":
            v[key] = value.total_seconds() * 1000
    return json.dumps(v, default=default)


class Example(BaseModel):
    delta_iso: timedelta # export using timedelta_isoformat
    delta_seconds_int: timedelta # export as int in seconds
    delta_seconds_float: timedelta # export as float in seconds
    delta_milliseconds_int: timedelta # export as int in milliseconds

    class Config:
        json_dumps = custom_dumps

diff = datetime.timedelta(milliseconds=5000)
print(Example(delta_iso=diff, delta_seconds_int=diff, delta_seconds_float=diff, delta_milliseconds_int=diff).json())

{"delta_iso": "P0DT0H0M5.000000S", "delta_seconds_int": 5, "delta_seconds_float": 5.0, "delta_milliseconds_int": 5000.0}

Pydantic：导出具有不同编码的相同类型的字段

Pydantic: Export fields of the same type with different encodings

python

pydantic