创建一个设置后不可变的字段

Question

是否可以创建一个没有默认值的 Pydantic 字段，并且该值必须在对象实例创建时设置并且从那时起不可变？

例如

from pydantic import BaseModel

class User(BaseModel):
    user_id: int
    name: str

user = User(user_id=1, name='John')
user.user_id = 2 # raises immutable error

Answer 1

如果要使所有字段不可变，可以将 class 声明为已冻结

class User(BaseModel):
    user_id: int
    name: str
    class Config:
        frozen = True

但是，这将使所有字段不可变，而不仅仅是特定字段

Answer 2

您可以尝试下面我的解决方案：

from pydantic import BaseModel, Field
class User(BaseModel):
    user_id: int
    name: str
    def setattr(cls, name, value):
        if name == "user_id": # or add more fiels here
            raise AttributeError("Cannot modify {}".format(name))
        else:
            return type.setattr(cls, name, value)

user = User(user_id=1, name='John')
user.user_id = 2 # raises immutable error

Answer 3

Pydantic 已有您想要的选项。您可以通过将 allow_mautation 指定为 false 来 customize 特定字段。如果在实例上分配了该字段，则会引发 TypeError。

from pydantic import BaseModel, Field


class User(BaseModel):
    user_id: int = Field(..., allow_mutation=False)
    name: str

    class Config:
        validate_assignment = True


user = User(user_id=1, name='John')
user.user_id = 2  # TypeError: "user_id" has allow_mutation set to False and cannot be assigned

创建一个设置后不可变的字段

Create a field which is immutable after being set

python

immutability

pydantic