I have a custom class which inherits from Python's built-in datetime.date
class:
# types.py
from datetime import date
class Date(date):
def __new__(cls, *args, isExceptional: bool = None, **kwargs):
if len(args) == 1 and isinstance(args[0], date):
self = super().__new__(
cls, args[0].year, args[0].month, args[0].day, **kwargs)
else:
self = super().__new__(cls, *args, **kwargs)
if isExceptional is not None:
self._isOff = True if self.isoweekday() in (6, 7) else False
if isExceptional:
self._isOff = not self._isOff
else:
self._isOff = None
return self
@property
def isOff(self):
return self._isOff
@isOff.setter
def isOff(self, value: bool):
if self._isOff is not None:
raise AttributeError(
"'isOff' can be set only when it is currently undefined,
i.e. None"
)
else:
self._isOff = value
In a word Date resembles the original date class, with an additional _isOff
attribute. Its constructor accepts as arguments either a standard date
object or whatever acceptable by the original date constructor, along with
an extra keyword-only one in order to manipulate _isOff value.
And a MariaDB (version 5.5) table:
CREATE TABLE `date` (
`date` DATE NOT NULL,
`isOff` BIT(1) NOT NULL DEFAULT b'0',
PRIMARY KEY (`date`)
)
COLLATE='utf8mb4_general_ci'
ENGINE=InnoDB
;
I can't figure out the "Declarative" way to map these two, so I tried
classical mapping:
# orm.py
import sqlalchemy as ORM
date = ORM.Table(
'date',
ORM.MetaData(),
ORM.Column('date', ORM.Date, primary_key=True),
ORM.Column('isOff', ORM.Boolean)
)
# types.py, after the Date class definition ...
from . import orm
from sqlalchemy.orm import mapper
mapper(Date, orm.date)
With these above, test = Date(2019, 9, 15) gives me
Traceback (most recent call last):
File
"c:\users\user\appdata\local\programs\python\python37-32\Lib\runpy.py",
line 193, in _run_module_as_main
"__main__", mod_spec)
File
"c:\users\user\appdata\local\programs\python\python37-32\Lib\runpy.py",
line 85, in _run_code
exec(code, run_globals)
File "D:\data\work\newsys\newsys\types.py", line 39, in <module>
test = Date(2019, 9, 15)
TypeError: __init__() takes 1 positional argument but 4 were given
I guess the __init__() mentioned in the error message comes from
SQLAlchemy's mapping mechanism, since there's no __init__() defined in my
class nor in the standard date class. Other than this, I can't figure out
what's going on... what's that "1 positional argument" supposed to be and
what are supplied as those 4?
How can I map them, with minimal modification to my Date class?
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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