Answer a question

I have a table that can have a status:

statuses = ['unmoderated', 'nominee', 'finalist', 'winner']
status = db.Enum(
    *statuses, name='enum_nomination_status', metadata=db.metadata)


class Nomination(db.Model):
    status = db.Column(status, default='unmoderated')

I would now like to have a table that has a column that can contain multiple statuses:

class Judge(db.Model):
    statuses = db.Column(ARRAY(status, dimensions=1))

However the above approach leads me to this error:

ProgrammingError: (psycopg2.ProgrammingError) column "statuses" is of type enum_nomination_status[] but expression is of type text[]
LINE 1: ...4, 'Name', ARRAY['unm...
                  ^
HINT:  You will need to rewrite or cast the expression.

So I tried to create a custom type that did the cast to the enum type:

class STATUS_ARRAY(TypeDecorator):
    impl = ARRAY(status, dimensions=1)

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        else:
            return cast(array(value), ARRAY(status, dimensions=1))

But this causes a segfault.

I've also tried casting the individual items:

class STATUS_ARRAY(TypeDecorator):
    impl = ARRAY(status, dimensions=1)

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        else:
            return array(cast(s, status) for s in value)

But I get:

ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'Cast' [SQL: 'INSERT INTO judge (statuses) VALUES (%(statuses)s)'] [parameters: {'statuses': [<sqlalchemy.sql.elements.Cast object at 0x7fc8bb69c710>]}]

I admit that I'm mostly trying different combinations of casting things without really knowing what's going on underneath the hood. I tried looking at the underlying ENUM implementation to see if I could get at some kind of native enum type without casting but I couldn't see anything. I'm grasping at straws.

Thanks for your help :)

Answers

As of 1.3.17, no workaround is needed anymore

The answer below ended up in the docs as ARRAY of ENUM. This docs page now says:

Changed in version 1.3.17: The combination of ENUM and ARRAY is now directly handled by SQLAlchemy’s implementation without any workarounds needed.

Old answer for historical purposes:

I looked at Issue 3467 posted by Wichert Akkerman, and this work-around was posted. Credit to Mike Bayer. Declare the following class in your code (with the necessary imports, of course):

from sqlalchemy.dialects.postgresql import ARRAY
from sqlalchemy import cast

class ArrayOfEnum(ARRAY):
    def bind_expression(self, bindvalue):
        return cast(bindvalue, self)

    def result_processor(self, dialect, coltype):
        super_rp = super(ArrayOfEnum, self).result_processor(dialect, coltype)

        def handle_raw_string(value):
            if value==None:
                return []
            inner = re.match(r"^{(.*)}$", value).group(1)
            return inner.split(",")

        def process(value):
            return super_rp(handle_raw_string(value))
        return process

ArrayOfEnum is now a special column type that gets used in the model definition.

So instead of

class Judge(db.Model):
    statuses = db.Column(ARRAY(status))

Now you can do:

class Judge(db.Model):
    statuses = db.Column(ArrayOfEnum(status))

Now in your code you can assign values to statuses with a list and it will do the proper casting upon saving:

my_judge_object.status = ['unmoderated', 'nominee']