Enum with another enum as keys

June 30, 2022

Im working on a project where adapters never raise Exceptions. Instead, it returns a Result object like this:

Dto = TypeVar("Dto", bound=BaseModel)


class BaseError(BaseModel):
    error_code: DomainErrorEnum
    message: str

    def raise_error(self):
        raise ErrorMap[self.error_code] # Here is the big deal


class Result(BaseModel, Generic[Dto]):
    error = Optional[BaseError]
    data: Optional[Dto]

Where DomainErrorEnum is an Enum that maps slugs that represent our DomainErrors.

What I like to do is a ErrorMap class that works like this:

class ErrorMap(DomainErrorEnum, Enum):
    DomainErrorEnum.GENERIC_ERROR = GenericErrorException
    DomainErrorEnum.NOT_FOUND = CartNotFoundException
    DomainErrorEnum.OUT_OF_STOCK = OutOfStockException

Doing this, I have 2 things well segregated:

An Enum (actually we have many "DomainErrorEnum", but Im pretending here that we have only one to make my example easy to understand) that has the responsability to represents (slugs) all my domain errors
A class that know which Exception it should throw whatever I want to trhow it (remember, my adapters never raise anything, it always return a Result[SpecificDto] object

Any idea on how to represent these 2 things?

Just for clarify:

# On domain module:
def specific_use_case():
    result_search: Result[ProductDto] = adapter.search_product()
    if product_dto.is_success:
        data: ProductDto = result_search.data
        result_search.business_rules_method(data) # Here, on pure business rules we throw exceptions without using our map, because here we dont use these Result pattern
        return entity

    result_search.error.raise_error()

>Solution :

ErrorMap should probably be a map (a dictionary):

ERROR_MAP = {
    DomainErrorEnum.GENERIC_ERROR: GenericErrorException,
    DomainErrorEnum.NOT_FOUND: CartNotFoundException,
    DomainErrorEnum.OUT_OF_STOCK: OutOfStockException
}