Remove an inherited field from a model in pydantic v2

[Top-Dog]

With pydantic v1 it was possible to exclude named fields in the child model if they were inherited from the parent with:

class Config:
        fields = {'clinic_id': {'exclude': True}}

The fields member variable has been removed in pydantic v2, so how can the same functionality be achieved? As a follow up question, what if the field is not inherited but part of a complex type in a model, for example, how to remove the id_ field from the following model in only one use case (CreatTicketOut):

class TicketCreate(BaseModel):
    clinic_id: int = Field(default=..., ge=0, description='Customer ID', example=24)
    text: str = Field(default=..., max_length=5000, description='Issuer', example='')
    id_: int # Internal ID for Database - I don't want to use Field(exclude=True, title="DB id") here because other models will inherit from TicketCreate and should include id_ and have access to it)

class CreatTicketOut(BaseModel):
    create_ticket: TicketCreate
    # Exclude only id_ in create_ticket?

See previous discussion of this topic for pydantic v1: #2686

[xtendch]

I am struggling with the same question. Currently my approach is to annotate attributes in inherited models as ClassVar as they are then automatically excluded. see https://docs.pydantic.dev/latest/usage/models/#automatically-excluded-attributes

But I am not sure what the implications and drawbacks of this approach are. Is it safe? Is it the best way forward?

Your example could then look like:

class TicketCreate(BaseModel):
    clinic_id: int = Field(default=..., ge=0, description='Customer ID', example=24)
    text: str = Field(default=..., max_length=5000, description='Issuer', example='')
    id_: int # Internal ID for Database - I don't want to use Field(exclude=True, title="DB id") here because other models will inherit from TicketCreate and should include id_ and have access to it)

class CreatTicketOut(TicketCreate):
    id_: ClassVar[int] # Exclude only id_ from field list of model instances

I love some of Pydantic V2's new features (e.g. @computed_field) but I am struggling in finding a convenient way to replace the exclude/include config for inherited models.

[sydney-runkle]

Hi, thanks for your question.

See this documentation for how to use the include and exclude arguments of the model_dump function to achieve what you're looking for. This documentation not only includes how to exclude fields of nested fields, as well as fields which take the form of lists or tuples.

Here's a basic example:

from pydantic import BaseModel
from typing import List


class Credentials(BaseModel):
    username: str
    password: str


class User(BaseModel):
    name: str
    credentials: Credentials

user = User(name="charles", credentials=Credentials(username="charles123", password="super-secret-pw"))

print(user.model_dump())
# > {'name': 'charles', 'credentials': {'username': 'charles123', 'password': 'super-secret-pw'}}
print(user.model_dump(exclude={"credentials": {"password"}}))
# > {'name': 'charles', 'credentials': {'username': 'charles123'}}

Feel free to let me know if you have any follow up questions!

[xtendch]

Thanks for your reply. But this is not really an option as it would required to make sure we exclude the credentials wherever we use the User model. For security reasons I would like to re-use a model as it was possible with pydantic V1.
E.g.

from pydantic import BaseModel
from typing import List


class Credentials(BaseModel):
    username: str
    password: str


class User(BaseModel):
    name: str
    credentials: Credentials

class UserOut(User):
    ...
    class Config:
        fields = {
            "credentials": {"exclude": True},
        }

Is there no efficient code-saving way to achieve this anymore?

[calmacx]

@xtendch did you get anywhere with this? I'm having the exact same issue

[xtendch]

Unfortunately I haven't found a good solution yet. For the meantime we are not switching to pydantic v2 as this point is very crucial and we made extensive use of the exclude.

[calmacx]

I found a pretty horrible hacky temporary solution:

class UserOut(BaseModel):
    ....

if type(UserOut.__fields_set__) == set:
      UserOut.__fields_set__.remove('credentials')
del UserOut.model_fields['credentials']

Doubt it'd be recommended/safe to do.. though is working for me, for now. I too would much prefer to be able to use "exclude" as in v1

[xtendch]

#2686 seems to be dealing with that question too. (But without an answer that sounds good to me.)

[xtendch]

Can anyone suggest a safe and good way to do this?

[xtendch]

I still don't have a satisfying answer to this problem, but omitting fields as suggested in #8516 could solve this issue too.

[H-G-11]

I think I found an easier answer below ⬇️

[H-G-11]

You can redefine the field in the child model, but with Field(..., exclude=True)

Here is the complete code:

from pydantic import Field, BaseModel

class Parent(BaseModel):
    a: int = 1

class Child(Parent):
    a: int = Field(default=1, exclude=True)

print(Parent(a=2).model_dump())
# returns {'a': 2}
print(Child().model_dump())
# returns {}

Works with pydantic v2.5.0

[bayangan1991]

Works to a point but unfortunately doesn't remove it from the schema or instance

>>> Child.model_json_schema()
{'properties': {'a': {'default': 1, 'title': 'A', 'type': 'integer'}}, 'title': 'Child', 'type': 'object'}
>>> Child()
a=1

[H-G-11]

I agree, but I don't think it has an impact for most use-cases, as in the end, what we mostly do is putting it in JSON format and uploading it somewhere.

Not sure what FastAPI would return in an endpoint returning Child()

[bayangan1991]

All my uses cases unfortunately use the schema :(

Can't generate reliable OpenAPI SDKs if the schema doesn't properly represent the object I need.

Back to handcrafting I guess.

[H-G-11]

Well, if the schema is the only issue, I guess this should work

from pydantic import Field, BaseModel
from pydantic.json_schema import SkipJsonSchema

class Parent(BaseModel):
    a: int = 1

class Child(Parent):
    a: SkipJsonSchema[int] = Field(default=1, exclude=True)

print(Parent(a=2).model_dump())
print(Child().model_dump())
print(Child.model_json_schema())

Outputs:

{'a': 2}
{}
{'properties': {}, 'title': 'Child', 'type': 'object'}

Having this kind of extra hidden field is not ideal, and am not a big fan of it neither, but that's a workaround

[seankerr]

Appreciate your resolution on this @H-G-11. This should be in the official documentation.

[xtendch]

ChatGPT brought me on the idea of using the @model_serialize decorator. Is there anything speaking against using this approach? Is using model_copy not ideal?

Example with include (which is nice, because you don't have to remember about excluding potentially sensitive attributes that have been added to the base model later):

class UserInput(BaseModel):
    username: str
    fullname: str
    sensitiveInformation: str
    password: str


class UserOutput(UserInput):
    ...

    @model_serializer
    def model_serialize(self):
        return self.model_copy(include={'username', 'fullname'})

see https://docs.pydantic.dev/2.7/api/functional_serializers/#pydantic.functional_serializers.model_serializer

[tteguayco]

I'm surprised Pydantic doesn't provide a method to exclude fields in an inherited model out of the box.

How can this be raised as a feature request?

Relates to: #9573