Cannot make db -> python value conversion working with custom SA columns

[avanov]

The definition:

import logging
import sqlalchemy.types as types
from enum import Enum as PythonEnum

log = logging.getLogger(__name__)

class PythonMappedEnum(types.TypeDecorator):
    """ Implements mapping between Postgres' Enums and Python Enums.
    """
    impl = types.Enum

    def __init__(self, python_enum_type: PythonEnum, **kwargs):
        self.python_enum_type = python_enum_type
        self.kwargs = kwargs
        enum_args = [x.value for x in python_enum_type]
        super(PythonMappedEnum, self).__init__(*enum_args, **self.kwargs)

    def process_bind_param(self, value: PythonEnum, dialect):
        """ Convert to postgres value
        """
        return value.value

    def process_result_value(self, value: str, dialect):
        """ Convert to python value
        """
        log.debug("=====================")
        log.debug("Called")
        for __, case in self.python_enum_type.__members__.items():
            if case.value == value:
                return case
        raise TypeError("Cannot map Enum value '{}' to Python's {}".format(
            value, self.python_enum_type
        ))

    def copy(self):
        return PythonMappedEnum(self.python_enum_type, **self.kwargs)

The calling code (abstract):

result = yield from SAPoolConnection.execute(SATable.select().limit(1))
data = yield from result.fetchone()

When data is processed, the value that corresponds to the custom Enum field is of type str, because the process_result_value() never gets called. But for insert statements, process_bind_param() is called as expected.

[avanov]

Relevant docs section

[TimNN]

I was about to report the same issue (took me a while to track this down).

As far as I can tell, the problem is that aiopg converts the types solely based on the oid of the type reported by postgresql (during my test process_bind_param does also not seem to be called I don't know how conversion happens there).

[TimNN]

@asvetlov you seem to be the main maintainer of this project, could you maybe chime in on this issue?

Is this (apart from this issue) a known weakness of aiopg and are there any plans to fix this? Or is there a technical reason that this is (currently) not possible to implement?

[asvetlov]

Guys, honestly I did not try custom types yet, so I don't know where it fails.

Maybe I'll find a time for investigation after fixing #20

[TimNN]

Don't feel pressured to fix this as soon as possible! I was just curious what the status was on this issue since there has never been an "official" response to this issue.

[serg666]

Have the same problem. process_bind_param() gets called, but process_result_value() never gets called

[serg666]

Guys, have any news about this issue? May be it can be fixed?

[asvetlov]

Nothing new I think.
At least I've failed with fix after couple hours of trying.

[vir-mir]

Better late than never #217

[jettify]

implemented in #217