How to enforce shallow copy for certain fields?

[eudoxos]

This is a MWE where I am passing around an object of type A, and would like to have the object shared among two instances of B. I write it the naive way but the A is getting copied automatically:

import pydantic

class A(pydantic.BaseModel):
    pass

class B(pydantic.BaseModel):
    a: A

b1=B(a=A())
b2=B(a=b1.a)

assert id(b1.a)==id(b2.a)

Is there a way around that?

[samuelcolvin]

see Config copy_on_model_validation

from pydantic import BaseModel

class A(BaseModel):
    pass

    class Config:
        copy_on_model_validation = False


class B(BaseModel):
    a: A


b1 = B(a=A())
b2 = B(a=b1.a)

assert id(b1.a) == id(b2.a)

Note that:

• you need to declare copy_on_model_validation on the inner model, not the outer
• copy_on_model_validation is new in v1.8

[eudoxos]

Cool, thanks!