嵌套字典到具有默认值的对象

Question

我正在使用 dataclasses + dataclasses_json 来实现我的网站 api。

我的应用程序会将请求从dict解码为object，我希望在没有填充每个字段的情况下仍然可以生成对象，并用默认值填充空字段。

这是我可能的代码：

from dataclasses import dataclass
from dataclasses_json import dataclass_json

@dataclass
class Glasses:
    color: str
    size: str
    prize: int

@dataclass
class Tshirt:
    color: str
    size: str
    prize: int

@dataclass_json
@dataclass
class People:
    Name : str = 'James'
    Age : int = 25
    Glasses: Glasses = Glasses('black', 'M', 2500)
    Tshirt: Tshirt = Tshirt('black', 'XL', 500)

p = {
    'Name': 'Gino',
    'Age': 20,
    'Glasses': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    },
    'Tshirt': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    }
}

a = People.from_dict(p)
print(a)

我会得到错误

Traceback (most recent call last):
  File ".\People.py", line 39, in <module>
    a = People.from_dict(p)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\api.py", line 83, in from_dict
    return _decode_dataclass(cls, kvs, infer_missing)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\core.py", line 133, in _decode_dataclass
    overrides = _user_overrides_or_exts(cls)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\core.py", line 59, in _user_overrides_or_exts
    if field.type in encoders:
TypeError: unhashable type: 'Glasses'

我发现我可以添加 (eq=True, frozen=True) 所以我将我的代码更改为

from dataclasses import dataclass
from dataclasses_json import dataclass_json

@dataclass(eq=True, frozen=True)
class Glasses:
    color: str
    size: str
    prize: int

@dataclass(eq=True, frozen=True)
class Tshirt:
    color: str
    size: str
    prize: int

@dataclass_json
@dataclass
class People:
    Name : str = 'James'
    Age : int = 25
    Glasses: Glasses = Glasses('black', 'M', 2500)
    Tshirt: Tshirt = Tshirt('black', 'XL', 500)

p = {
    'Name': 'Gino',
    'Age': 20,
    'Glasses': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    },
    'Tshirt': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    }
}

a = People.from_dict(p)
print(a)

我遇到了另一个错误

  File ".\People.py", line 39, in <module>
    a = People.from_dict(p)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\api.py", line 83, in from_dict
    return _decode_dataclass(cls, kvs, infer_missing)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\core.py", line 198, in _decode_dataclass
    infer_missing)
  File "C:\Python3.7\lib\site-packages\dataclasses_json\core.py", line 131, in _decode_dataclass
    if isinstance(kvs, cls):
TypeError: isinstance() arg 2 must be a type or tuple of types

有没有什么方法可以使用内置函数来满足我的要求，而无需自己编写代码？

Answer 1

您有字段名称和类型名称冲突。为了让你的代码工作，你必须有 JSON 字段的名称不同于 classes 名称，即你不能有字段 "Glasses" 和 class Glasses ，您必须将 class 重命名为 Glasses_ 或重命名您的字段名称。

另一种选择是为 classes 类型创建别名，即为 Glasses.

创建别名 GlassesT

类型别名的代码版本：

Try it online!

from dataclasses import dataclass
from dataclasses_json import dataclass_json

@dataclass
class Glasses:
    color: str
    size: str
    prize: int

GlassesT = Glasses

@dataclass
class Tshirt:
    color: str
    size: str
    prize: int
    
TshirtT = Tshirt
    
@dataclass_json
@dataclass
class People:
    Name : str = 'James'
    Age : int = 25
    Glasses: GlassesT = GlassesT('black', 'M', 2500)
    Tshirt: TshirtT = TshirtT('black', 'XL', 500)

p = {
    'Name': 'Gino',
    'Age': 20,
    'Glasses': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    },
    'Tshirt': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    }
}

a = People.from_dict(p)
print(a)

输出：

People(Name='Gino', Age=20, Glasses=Glasses(color='red', size='M', prize=4000), Tshirt=Tshirt(color='red', size='M', prize=4000))

重命名后的代码版本 classes:

Try it online!

from dataclasses import dataclass
from dataclasses_json import dataclass_json

@dataclass
class Glasses_:
    color: str
    size: str
    prize: int

@dataclass
class Tshirt_:
    color: str
    size: str
    prize: int

@dataclass_json
@dataclass
class People:
    Name : str = 'James'
    Age : int = 25
    Glasses: Glasses_ = Glasses_('black', 'M', 2500)
    Tshirt: Tshirt_ = Tshirt_('black', 'XL', 500)

p = {
    'Name': 'Gino',
    'Age': 20,
    'Glasses': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    },
    'Tshirt': {
        'color' : 'red',
        'size' : 'M',
        'prize' : 4000
    }
}

a = People.from_dict(p)
print(a)

输出：

People(Name='Gino', Age=20, Glasses=Glasses_(color='red', size='M', prize=4000), Tshirt=Tshirt_(color='red', size='M', prize=4000))

嵌套字典到具有默认值的对象

Nested dict to object with default value

python

python-3.7

python-dataclasses