python - 在从 pydantic.BaseModel 创建的 JSON 中，如果未设置，则排除可选

Question

我想排除所有在创建 JSON 时未设置的 Optional 值。在这个例子中:

from pydantic import BaseModel
from typing import Optional


class Foo(BaseModel):
    x: int
    y: int = 42
    z: Optional[int]


print(Foo(x=3).json())

我收到 {"x": 3, "y": 42, "z": null} .但我想排除 z .不是因为它的值是 None , 但因为它是 Optional 并且没有 z 的关键字参数.在下面的两种情况下，我想要 z在 JSON 中。

Foo(x=1, z=None)
Foo(x=1, z=77)

如果有任何其他解决方案可以设置 z从这个意义上讲，我希望看到它。

Answer 1

您可以仅排除未设置的可选模型字段，方法是建立 的模型字段的并集。已设置 和那些不是无 .
Pydantic 为导出方法提供以下参数 model.dict(...) :

exclude_unset: whether fields which were not explicitly set when creating the model should be excluded from the returned dictionary; default False.

exclude_none: whether fields which are equal to None should be excluded from the returned dictionary; default False

要合并两个字典，我们可以使用表达式 a = {**b, **c} (来自 c 的值覆盖来自 b 的值)。请注意，从 Python 3.9 开始，它可以像 a = b | c 一样完成。 .

from pydantic import BaseModel
from typing import Optional
from pydantic.json import pydantic_encoder
import json


class Foo(BaseModel):
    x: int
    y: int = 42
    z: Optional[int]

def exclude_optional_dict(model: BaseModel):
    return {**model.dict(exclude_unset=True), **model.dict(exclude_none=True)}

def exclude_optional_json(model: BaseModel):
    return json.dumps(exclude_optional_dict(model), default=pydantic_encoder)
    


print(exclude_optional_json(Foo(x=3)))  # {"x": 3, "y": 42}
print(exclude_optional_json(Foo(x=3, z=None)))  # {"x": 3, "z": null, "y": 42}
print(exclude_optional_json(Foo(x=3, z=77)))  # {"x": 3, "z": 77, "y": 42}

更新
为了使用嵌套模型的方法，我们需要对两个字典进行深度联合(或合并)，如下所示:

def union(source, destination):
    for key, value in source.items():
        if isinstance(value, dict):
            node = destination.setdefault(key, {})
            union(value, node)
        else:
            destination[key] = value

    return destination

def exclude_optional_dict(model: BaseModel):
    return union(model.dict(exclude_unset=True), model.dict(exclude_none=True))

class Foo(BaseModel):
    x: int
    y: int = 42
    z: Optional[int]

class Bar(BaseModel):
    a: int
    b: int = 52
    c: Optional[int]
    d: Foo


print(exclude_optional_json(Bar(a=4, d=Foo(x=3))))
print(exclude_optional_json(Bar(a=4, c=None, d=Foo(x=3, z=None))))
print(exclude_optional_json(Bar(a=4, c=78, d=Foo(x=3, z=77))))

{"a": 4, "b": 52, "d": {"x": 3, "y": 42}}
{"a": 4, "b": 52, "d": {"x": 3, "y": 42, "z": null}, "c": null}
{"a": 4, "b": 52, "c": 78, "d": {"x": 3, "y": 42, "z": 77}}