When I specify the API and schema in FastAPI (OpenAPI) and let FastAPI generate the schema objects/classes, the member names are formatted snake case and get a alias name in camel case.

class ObjectIdentifier(BaseModel):
    """NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).

    Do not edit the class manually.

    ObjectIdentifier - a model defined in OpenAPI

        location: The location of this ObjectIdentifier.
        location_type: The location_type of this ObjectIdentifier.
    """

    location: str = Field(alias="location")
    location_type: str = Field(alias="locationType")

ObjectIdentifier.update_forward_refs()

But when I populate a Pydantic class using its constructor and a dictionary from a database result set, the dictionary needs to contain the keys (attribute names) written with camel case.

# code that works
object_info = ObjectInformation(
    objectId=ObjectIdentifier(location=location, locationType=location_type),
    objectInfo=object_info
)

# code that does not work
object_info = ObjectInformation(
    object_id=ObjectIdentifier(location=location, location_type=location_type),
    object_info=object_info
)

Can I make the generated Pydantic code use snake case attribte names?

I tried several approaches using alias_generators and the Config object within a custom base class, but I can not use these approaches, as the Pydantic code is generated and I did not yet figure out how to use them in my context.

Ideally, I can use a syntax like this:

object_info = ObjectInformation(**database_result)

with database_result like this:

database_result = dict(
    location: "some location",
    location_type: "some location type",
    object_info: "the important object info"
)

That dictionary is a result of a query to a SQL DB, I can not get camel case attribute names as the DB access converts every name to lowercase. Thus, I can only get snake case from the DB results.

Notice, that the Pydantic structure is nested, ObjectIdentifier inside ObjectInformation. I dont know if nesting should work like I tried it.

Python: 3.9
Pydantic: 3.10.15