Hello,
I have a heavy method of a class (not mapped with SQLA) that takes as
argument some SQLA instances (with relationships), does some operation on
them (without using any SQLA feature), and returns a subset of them. The
logic was working before I added the SQLAlchemy persistence layer using
pathos.multiprocessing.
In my full code I get a recursion depth exceeded error, and I was not able
to reproduce the problem with a MWE. By the way with a MWE I get a "Can't
picke <class 'sqlalchemy.ext.declarative.api.Base'>: it's not found as
sqlalchemy.ext.declarative.api.Base". I suppose that I should define
__getstate__ and __setstate__ magic methods stripping out all the SQLA
"stuff" inside the instance. Is this right? Or there is something I'm not
considering? Will I be able to reconstitute the instance after the
pickling/unpickling? How does it work with the persistence with the
underlying session? Are there any examples for this?
Thanks in advance for the great support and help in this mailing list,
from sqlalchemy import Column, Integer, String, DateTime, Float,\
ForeignKey
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from pyggdrasill.sql.schema import connect_db
from datetime import datetime
import pathos.multiprocessing as mpp
from functools import partial
Base = declarative_base()
class Sensor(Base):
__tablename__ = 'sensor'
id = Column(Integer, primary_key=True)
name = Column(String(150))
readings = relationship("Reading", backref='sensor',
cascade='all, delete-orphan')
def __init__(self, name):
self.name = name
def read(self, room):
return [
Reading(
self,
room,
datetime.now(),
10.0),
Reading(
self,
room,
datetime.now(),
20.0),
Reading(
self,
room,
datetime.now(),
30.0)
]
class Room(Base):
__tablename__ = 'room'
id = Column(Integer, primary_key=True)
name = Column(String(150))
readings = relationship("Reading", backref='room',
cascade='all, delete-orphan')
def __init__(self, name):
self.name = name
class Reading(Base):
__tablename__ = 'reading'
id = Column(Integer, primary_key=True)
date = Column(DateTime)
voltage = Column(Float)
sensor_id = Column(Integer, ForeignKey('sensor.id'), nullable=False)
room_id = Column(Integer, ForeignKey('room.id'), nullable=False)
def __init__(self, sensor, room, date, voltage):
self.sensor = sensor
self.room = room
self.date = date
self.voltage = voltage
def __repr__(self):
return '<Read {} {}>'.format(self.date, self.voltage)
if __name__ == '__main__':
db = connect_db(
username='pygg',
password='albero della vita',
db_name='pyggdrasill',
echo=False)
Base.metadata.create_all(db)
S = sessionmaker(db)
session = S()
def mp_read(room, useless):
sensor = Sensor('Pressure Sensor')
return Room(sensor,
room,
datetime.now(),
20.0)
#readings = sensor.read(room)
pool = mpp.Pool()
partial_read = partial(mp_read, useless=None)
rooms = [Room('bedroom'), Room('Living'), Room('kitchen')]
readings = pool.map(partial_read, rooms)
# session.add(sensor)
# session.commit()
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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