Serializing native Python enums does not work

Currently using SQL enums works well, unless you use a enum.Enum as base for the enum. For example using this model:

class Hairkind(enum.Enum):
    LONG = 'long'
    SHORT = 'short'

class Pet(Base):
    __tablename__ = 'pets'
    id = Column(Integer(), primary_key=True)
    hair_kind = Column(Enum(Hairkind, name='hair_kind'), nullable=False)

will fail badly if you try to query the hairKind field:

  File "lib/python3.7/site-packages/graphql/execution/executor.py", line 622, in complete_leaf_value
    path=path,
graphql.error.base.GraphQLError: Expected a value of type "hair_kind" but received: Hairkind.LONG

[wichert]

What is happening here is that graphqln_sqlalchemy.converter.convert_sqlalchemy_type.register creates a GraphQL Enum using the enum instances using items = type.enum_class.__members__.items(). But in graphql.type.definition.GraphQLEnumType.serialize this happens:

    def serialize(self, value):
        # type: (Union[str, PyEnum]) -> Optional[str]
        if isinstance(value, PyEnum):
            # We handle PyEnum values
            value = value.value
        if isinstance(value, collections.Hashable):
            enum_value = self._value_lookup.get(value)
            if enum_value:
                return enum_value.name

        return None

at that point the enum.Enum instance is converted to its value, which is then looked up. But the lookup table has the enum instances, causing the lookup to fail and an error to be returned.

[robjampar]

Yeah this has broken enums in one of my libraries and the only way i can fix it is to monkey patch the method!

id suggest a non breaking change, for example:

def serialize(self, value):
    if isinstance(value, collections.Hashable):
        if value in self._value_lookup:
            enum_value = self._value_lookup.get(value)
    
        elif isinstance(value, PyEnum):
            # We handle PyEnum values
            enum_value = self._value_lookup.get(value.value)
    
        if enum_value:
            return enum_value.name
    
    return None```