Mapping Db Varchar To Domain Object Bool

How do I handle the mapping of strings in the database to bools in the domain model. Consider an example, storing coin flips in a database. For cases where there are usually only t

Solution 1:

Take a look at Augmenting Existing Types section of documentation. The following should do the trick:

import sqlalchemy.types as types


class CoinFlipDataType(types.TypeDecorator):
    impl = types.String

    def process_bind_param(self, value, dialect):
        if value is None:
            return None
        assert value in (True, False)
        return 'heads' if value else 'tails'

    def process_result_value(self, value, dialect):
        if value is None:
            return None
        assert value in ('heads', 'tails'), value
        return value == 'heads'

    def copy(self):
        return CoinFlipDataType(self.impl.length)

def data_map():
    mapper(Foo, db_foo, properties={'is_heads': db_foo.c.side})

db_foo = Table(
    'foo', metadata,
    Column('id', Integer, primary_key=True),
    Column('side', CoinFlipDataType(5), nullable=False))