I came accross from_attributes today it allows creation of pydantic models from objects such as a sqlalchemy Base Model or while nesting pydantic models. I believe in the past I have ran into some inconsistencies with nesting pydantic models and I'll bet one had from_attributes set and another did not.
Arbitrary class instances¶ (Formerly known as "ORM Mode"/from_orm).
Pydantic models can also be created from arbitrary class instances by reading the instance > attributes corresponding to the model field names. One common application of this functionality is integration with object-relational mappings (ORMs).
To do this, set the from_attributes config value to True (see the documentation on Configuration for more details).
The example here uses SQLAlchemy, but the same approach should work for any ORM.