Model copy(update=) not validating

Question

Currently calling copy with update= does not validate the updated data and we can end up with odd cases like this:

import pydantic

class ChildModel(BaseModel):
    v: int

class Model(BaseModel):
    c: ChildModel

>>> m = Model(c={"v": 5})
>>> print(m.c)
ChildModel v=5

>>> m2 = m.copy(update={"c": {"v": 3}})
>>> print(m2.c)
{'v': 3}

One can also imagine a case where the updated data is completely incorrect as well. A current workaround would be to do the following:

>>> m3 = m.copy(update={"c": m.c.copy(update={"v": 3})})
>> print(m3.c)
ChildModel v=3

This seems a bit awkward. A possible fix would be to call __init__ rather than construct in the copy constructor if update is not None. We use this feature quite a bit to alter immutable models.

[indigoSam]

I think best to implement this in our own logic.

@samuelcolvin 👋😸 Was this ever implemented? Or should we still use community solutions? Thank you!

[samuelcolvin]

how about update complies with validate_assignment, eg. it’s validated only if validate_assignment = True?