[BUG] Updating documents with a frozen BaseModel as field raises TypeError

[Mark90]

Describe the bug
Relating a document X to document Y using Link[], with document Y having a pydantic.BaseModel field that has class Config: frozen = True, will trigger the error TypError: <field> is immutable in Pydantic.

To Reproduce

edit please check my comment below, there is an easier way to reproduce it.

class PersonDetails(BaseModel):
    ssn: int
    dob: str

    class Config:
        frozen = True

class Person(Document):
    first_name: str
    last_name: str
    details: PersonDetails

class House(Document):
    name: str
    people: list[Link[Person]]


await init_beanie(database=db, document_models=[House, Person])

person = Person(first_name="john", last_name="doe", details=PersonDetails(ssn=123, dob="01/01/1970"))
house = House(name="my house", people=[person])
await house.insert(link_rule=WriteRules.WRITE)
print(f"Created {house=}")

Outputs:

TypeError: "PersonDetails" is immutable and does not support item assignment

When I first create the Person document and then try to link this to the House, it fails on the linking action;

person = Person(first_name="john", last_name="doe", details=PersonDetails(ssn=123, dob="01/01/1970"))
await person.insert()
print(f"Created {person=}")

house = House(name="my house", people=[person])
await house.insert(link_rule=WriteRules.WRITE)
print(f"Created {house=}")

It successfully performs person.insert() and then raises the error at the `house.insert():

Created person=Person(id=ObjectId('649450d942a9b7dbc587940b'), revision_id=None, first_name='john', last_name='doe', details=PersonDetails(ssn=123, dob='01/01/1970'))
Traceback (most recent call last):
... (ommitted)
  File "/usr/local/lib/python3.11/site-packages/beanie/odm/documents.py", line 607, in update
    merge_models(self, result)
  File "/usr/local/lib/python3.11/site-packages/beanie/odm/utils/parsing.py", line 24, in merge_models
    merge_models(left_value, right_value)
  File "/usr/local/lib/python3.11/site-packages/beanie/odm/utils/parsing.py", line 35, in merge_models
    left.__setattr__(k, right_value)
  File "pydantic/main.py", line 359, in pydantic.main.BaseModel.__setattr__
TypeError: "PersonDetails" is immutable and does not support item assignment

Ways to not get this error:

• Rewrite to 2-step approach and leave out the link_rule=WriteRules.WRITE (viable workaround, but quite verbose)
• Remove frozen = True (not a viable workaround in my case)

Expected behavior

Same as when Person would not be a Document but just a BaseModel;

class PersonDetails(BaseModel):
    ssn: int
    dob: str

    class Config:
        frozen = True

class Person(BaseModel):
    first_name: str
    last_name: str
    details: PersonDetails

class House(Document):
    name: str
    people: list[Person]


await init_beanie(database=db, document_models=[House])

person = Person(first_name="john", last_name="doe", details=PersonDetails(ssn=123, dob="01/01/1970"))
house = House(name="my house", people=[person])
await house.insert(link_rule=WriteRules.WRITE)
print(f"Created {house=}")

Which inserts without problems:

Created house=House(id=ObjectId('64944f0e5d3bc3eb3a5b495e'), revision_id=None, name='my house', people=[Person(first_name='john', last_name='doe', details=PersonDetails(ssn=123, dob='01/01/1970'))])

Additional context

n/a

[Mark90]

Actually, it looks like Link is irrelevant here. I can reproduce it with this smaller example where I create and then update a document:

class PersonDetails(BaseModel):
    ssn: int
    dob: str

    class Config:
        frozen = True


class Person(Document):
    first_name: str
    last_name: str
    details: PersonDetails

    class Settings:
        use_state_management = True


await init_beanie(database=db, document_models=[Person])

person = Person(first_name="john", last_name="doe", details=PersonDetails(ssn=123, dob="01/01/1970"))
await person.insert()
print(f"Created {person=}")

person.first_name = "jane"
# await person.save()  # TypeError: "PersonDetails" is immutable and does not support item assignment
await person.save_changes()  # TypeError: "PersonDetails" is immutable and does not support item assignment
print(f"Updated {person=}")

The .insert() works, but when I update any (non-frozen) attribute, both .save() and .save_changes() raise the already mentioned TypeError

Created person=Person(id=ObjectId('6495af9d20f78b1f0b244ee7'), revision_id=None, first_name='john', last_name='doe', details=PersonDetails(ssn=123, dob='01/01/1970'))
Traceback (most recent call last):
  ... (ommitted)
  File "/usr/local/lib/python3.11/site-packages/beanie/odm/utils/parsing.py", line 24, in merge_models
    merge_models(left_value, right_value)
  File "/usr/local/lib/python3.11/site-packages/beanie/odm/utils/parsing.py", line 35, in merge_models
    left.__setattr__(k, right_value)
  File "pydantic/main.py", line 359, in pydantic.main.BaseModel.__setattr__
TypeError: "PersonDetails" is immutable and does not support item assignment

[Mark90]

In 1.17.0 this doesn't occur, it seems to have been introduced in 1.18.0

[roman-right]

Hello,
I'll check this. Thank you for the catch

[jayrahdevore]

Just ran into this as well. Rolling back to 1.17.0 took care of the issue

[roman-right]

This bug is fixed in #669. Please try

[Mark90]

Thank you!

Actually it already seems to have been fixed in version 1.21.0, when I upgrade to that version all of our testcases pass (and on 1.20.0 they didn't pass yet). Awesome :)

When I pip install -U git+https://github.com/roman-right/beanie.git@fix/aug_2023 I see some new errors in our tests, I'll leave a comment on that PR.