Pydantic: alias_generator not working if there are extra (non-alias) fields

[gmetzker]

Bug

Depending on your point of view this might not be a bug but it would be cool to address in any case.

For my models I have special field configurations that I add to the Config.fields. I recently tried the alias_generator option on the Config to force fields to camel case. The problem is when Config.get_field_schema runs it thinks there is a field config so it skips the alias_generator.

It makes sense to skip it if there is an alias but in my case there are other field options but not an alias.

For bugs/questions:

• OS: OSX
• Python version import sys; print(sys.version): 3.7.3
• Pydantic version import pydantic; print(pydantic.VERSION): 0.30.0

Where possible please include a self contained code snippet describing your
bug, question, or where applicable feature request:

import pydantic
import stringcase

Person(BaseModel)
  first_name: str
  last_name: str
  class Config:
    alias_generator = stringcase.camelcase
    fields = {
        "first_name": { "myCustomOp": True }
    }

person = Person(first_name="Arthur" last_name="Dent")
d = person.dict(by_alias=True)
# {"first_name": "Arthur", "lastName": "Dent"}

Proposed Solution

Run the generator if it is present and 'alias' is not present.

How does this look for a fix?

@classmethod
def get_field_schema(cls, name: str) -> Dict[str, str]:

    field_config = cls.fields.get(name) or {}

    if isinstance(field_config, str):
        field_config = {'alias': field_config}

    elif cls.alias_generator:

        if not field_config or 'alias' not in field_config:

            alias = cls.alias_generator(name)
            if not isinstance(alias, str):
                raise TypeError(f'Config.alias_generator must return str, not {type(alias)}')

            if not field_config:
                field_config = {}

            field_config['alias'] = alias

    return field_config

[MrMrRobat]

Thanks for the issue, seems like a bug for me. I'll make PR with fix soon