On Thu, Jul 27, 2017 at 4:43 PM, Mike Bayer <[email protected]> wrote:
> On Thu, Jul 27, 2017 at 10:50 AM, Ruben Di Battista
> <[email protected]> wrote:
>> Hello, I'm trying to figure out a streamlined way to store some children
>> values that are stored in numpy arrays in Python. As example let's assume I
>> have a parent object that is a sensor that has some readings associated to
>> it:
>>
>> class Sensor(object):
>> __tablename__ = 'sensor'
>> id = Column(Integer, primary_key=True),
>> name = Column(String)
>> readings = relationship("Reading", backref="sensor")
>>
>>
>> class Reading(object):
>> __tablename__ = 'reading'
>> id = Column(Integer, primary_key=True),
>> date = Column(DateTime),
>> voltage = Column(Float),
>> value = Column(Float),
>>
>> sensor_id = Column(Integer, ForeignKey('sensor.id'))
>>
>>
>> What I would like to achieve is something like:
>> sensor = Sensor(name='Bedroom Sensor')
>> dates, voltages, values = get_sensor_data_from_somewhere() #<-- This
>> returns three numpy arrays respectively of datetime, float, float types,
>> same len!
>>
>> sensor.readings['date'] = dates
>> sensor.readings['voltage'] = voltages
>> sensor.values['value'] = values
oh, .readings. Unfortunately you'd need to develop a custom
collection class which achieves this and make it available by a
@property on Sensor:
class Sensor(...):
@property
def readings(self):
return MagicReadingCollection(self)
then you do the __getitem__ / __setitem__ thing on MagicReadingCollection:
class MagicReadingCollection(object):
def __init__(self, sensor):
self.sensor = sensor
def __setitem__(self, field, values):
start_appending_at = len(self.sensor.readings)
for index, value in enumerate(values):
if index > start_appending_at:
reading = Reading()
self.sensor.readings.append(reading)
else:
reading = self.sensor.readings[index]
setattr(reading, field, value)
>>
>> session.add(sensor)
>>
>> Is this possible somehow? It's similar to the attribute_mapped_collection,
>> but I need to map three different keys to the three attributes of the
>> Reading object.
>
> Application of appropriate __getitem__() and __setitem__() methods on
> your Sensor class would achieve this.
>
>
>>
>> --
>> 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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--
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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