On Wed, Aug 22, 2018 at 5:50 AM, Alexios Damigos <[email protected]> wrote:
> Hello everyone,
>
> I have been trying to create a model for my database, with no luck so far.
> I am using SQLAlchemy 1.2.10 together with PyMySQL 0.9.2 to connect to a
> MariaDB database.
>
> A description of the database model:
>
> Table A (components)
> id brand status
> N1 br3 free
> N2 br2 used
> N3 br2 used
> N4 br3 used
> N5 br2 used
> N6 br3 used
> N7 br2 used
>
>
> Table B (device1)
> id comp1 comp2
> 2 N2 N3
>
> Table C (device2)
> id comp1 comp2
> 6 N4 N5
>
> Table D (device3)
> id comp1 comp2
> 1 N6 N7
>
> So there are two foreign keys pointing to the same table (A) and column for
> all the other three tables, and every item on table A can only be assigned
> to a singe component column of a single table B, C or D.
>
> Ideally what I would like to achieve is something like this:
>
> component1 -> <N2 br2 used>
> component1.deviceInstalled -> <2 N2 N3> (from table B)
> component2 -> <N4 br3 used>
> component2.deviceInstalled -> <6 N4 N5> (from table C)
>
> I tried following the guidelines in Multiple Join Paths, still got ambiguous
> foreign keys error.
> As far as the relationship deviceInstalled, I have not managed to find
> somewhere how to implement that, since it has to span across three tables.
>
>
> My working but incomplete code at the moment, with all the failed attempts
> removed.
Looking at the code, I dont know what:
ForeignKey('')
means, I guess that means you don't know which table to refer towards?
if batmon/radmon/deported are B, C, and D, and "Sensor" is not part of
the problem, just make them FK's to"Device"? Here's that
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
Model = declarative_base()
class Device(Model):
__tablename__ = 'device'
id = Column(Integer, primary_key=True)
type = Column(String(30), unique=False, nullable=False)
variant = Column(String(30), unique=False, nullable=True)
serialNo = Column(String(30), unique=True, nullable=False)
batmonConf = relationship('Batmon', backref='device',
uselist=False, lazy=True)
radmonConf = relationship('Radmon', backref='device',
uselist=False, lazy=True)
deportedConf = relationship('Deported', backref='device',
uselist=False, lazy=True)
class Batmon(Model):
__tablename__ = 'batmon'
id = Column(Integer, ForeignKey('device.id'), primary_key=True)
voltage = Column(Integer, unique=False, nullable=False)
fet1 = Column(String(20), ForeignKey(''), unique=True)
fet2 = Column(String(20), unique=True, nullable=True)
pin = Column(String(20), unique=True, nullable=True)
mem1 = Column(String(20), unique=True, nullable=True)
mem2 = Column(String(20), unique=True, nullable=True)
class Radmon(Model):
__tablename__ = 'radmon'
id = Column(Integer, ForeignKey('device.id'), primary_key=True)
fet1 = Column(String(20), unique=True, nullable=True)
fet2 = Column(String(20), unique=True, nullable=True)
pin = Column(String(20), unique=True, nullable=True)
mem1 = Column(String(20), unique=True, nullable=True)
mem2 = Column(String(20), unique=True, nullable=True)
class Deported(Model):
__tablename__ = 'deported'
id = Column(Integer, ForeignKey('device.id'), primary_key=True)
fet1 = Column(String(20), unique=True, nullable=True)
fet2 = Column(String(20), unique=True, nullable=True)
pin = Column(String(20), unique=True, nullable=True)
configure_mappers()
>
> Any help would be very much appreciated, as I have been trying for a couple
> of days with no luck!
> Thank you
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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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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