Here's a standalone working example:
import sqlalchemy as sa
import sqlalchemy.orm as saorm
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Objekt(Base):
__tablename__ = "objekt"
id = sa.Column(sa.Integer, primary_key=True)
typ_id = sa.Column(sa.Integer, sa.ForeignKey("objekt_typ.id"))
typ = saorm.relationship("ObjektTyp")
name = sa.Column(sa.String(100))
__mapper_args__ = {
"polymorphic_on": typ_id,
}
class ObjektTyp(Base):
__tablename__ = "objekt_typ"
id = sa.Column(sa.Integer, primary_key=True)
name = sa.Column(sa.String(100))
class ChildObjekt1(Objekt):
__tablename__ = "child_objekt1"
id = sa.Column(sa.Integer, sa.ForeignKey(Objekt.id), primary_key=True)
text = sa.Column(sa.String(255))
__mapper_args__ = {
"polymorphic_identity": 1,
}
class ChildObjekt2(Objekt):
__tablename__ = "child_objekt2"
id = sa.Column(sa.Integer, sa.ForeignKey(Objekt.id), primary_key=True)
text = sa.Column(sa.String(255))
__mapper_args__ = {
"polymorphic_identity": 2,
}
if __name__ == "__main__":
engine = sa.create_engine("sqlite://")
Base.metadata.create_all(bind=engine)
Session = saorm.sessionmaker(bind=engine)
session = Session()
child1type = ObjektTyp(id=1, name="child1")
child2type = ObjektTyp(id=2, name="child1")
child1 = ChildObjekt1(text="child 1 text")
child2 = ChildObjekt2(text="child 2 text")
session.add_all([child1type, child2type, child1, child2])
session.flush()
for obj in session.query(Objekt):
print(obj)
Simon
On Mon, Apr 12, 2021 at 6:40 PM 'Sören Textor' via sqlalchemy
<sqlalchemy@googlegroups.com> wrote:
>
> class Objekt(db.Model):
> __tablename__ = 'objekt'
>
> def __init__(self,**kwargs):
> super().__init__(**kwargs)
>
> id = db.Column(db.Integer, primary_key=True)
> typ_id = db.Column(db.Integer, db.ForeignKey('objekt_typ.id'))
> typ = db.relationship("ObjektTyp")
> name = db.Column(db.String(100))
>
> __mapper_args__ = {
> 'polymorphic_on': typ_id
> }
>
> class ChildObjekt1(Objekt):
> __versioned__ = {}
> __tablename__ = 'child_objekt1'
>
> @staticmethod
> def TypId():
> return 7
>
> # User fields
> def __init__(self,**kwargs):
> super().__init__(**kwargs)
> #super().__init__(typ_id=ChildObjekt1.TypId(), **kwargs)
>
> ###
> id db.Column(db.Integer, db.ForeignKey('objekt.id'),
> primary_key=True)
> text = db.Column(db.String(255 ), default='')
>
> __mapper_args__ = {
> 'polymorphic_identity': 7,
> }
>
>
> leads to:
> venv\lib\site-packages\sqlalchemy\orm\mapper.py", line 1542, in
> _configure_polymorphic_setter
> self.polymorphic_on = self._props[self.polymorphic_on]
> KeyError: 'typ_id'
>
> raise exception
> sqlalchemy.exc.ArgumentError: Can't determine polymorphic_on value
> 'typ_id' - no attribute is mapped to this name.
>
> maybe i do something totally worg.. I am also using sql continuum
>
> ------ Originalnachricht ------
> Von: "Simon King" <si...@simonking.org.uk>
> An: sqlalchemy@googlegroups.com
> Gesendet: 12.04.2021 19:06:11
> Betreff: Re: [sqlalchemy] Invertinace mapped type_id to fix value for
> each child class
>
> >I don't understand this comment:
> >
> >> I though on polymorphic_on, but I think that does not work because of the
> >> fact that type_id ha a foreign key ...
> >
> >As far as I can tell, you ought to have this in the base class:
> >
> > __mapper_args__ = {
> > 'polymorphic_on': typ_id
> > }
> >
> >And this in the subclass:
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 7,
> > }
> >
> >...and you should get rid of the typ_id function and the
> >"Objekt.typ_id = ChildClass.typ_id" line.
> >
> >Does that work for you?
> >
> >Simon
> >
> >On Mon, Apr 12, 2021 at 5:18 PM 'Sören Textor' via sqlalchemy
> ><sqlalchemy@googlegroups.com> wrote:
> >>
> >> I run into a problem and don't know how to solve it.
> >> The theory is very simple: I habe one base class table with name, id and
> >> type column
> >> The child class shall have a unique type_id (all child_class1 objekt
> >> shall get type_id 7, all child_class2 objekts type_id = 8, ...)
> >>
> >> How can I map the base class typ_id to an hard coded value for eahc class
> >> type.
> >> My actual approach does not change the type_id-columns of Objekt and
> >> after saving the objekt the column Objekt.type_id entry is always empty
> >> for all entries :-(
> >>
> >> class Objekt(db.Model):
> >> __tablename__ = 'objekt'
> >>
> >> def __init__(self,**kwargs):
> >> super().__init__(**kwargs)
> >>
> >> id = db.Column(db.Integer, primary_key=True)
> >> typ_id = db.Column(db.Integer, db.ForeignKey('objekt_typ.id'))
> >> typ = db.relationship("ObjektTyp")
> >> name = db.Column(db.String(100))
> >>
> >> class ChildClass1(Objekt):
> >> __tablename__ = 'child_class1'
> >>
> >> @staticmethod
> >> def typ_id():
> >> return 7
> >>
> >> def __init__(self,**kwargs):
> >> super().__init__(**kwargs)
> >> Objekt.typ_id = ChildClass1.typ_id() ### fix type
> >>
> >> id = db.Column(db.Integer, db.ForeignKey('objekt.id'),
> >> primary_key=True)
> >> text = db.Column(db.String(255 ), default='')
> >>
> >> __mapper_args__ = {
> >> 'polymorphic_identity':'child_class1',
> >> }
> >>
> >>
> >> any ideas where to look? I though on polymorphic_on, but I think that
> >> does not work because of the fact that type_id ha a foreign key ...
> >>
> >> SirAnn
> >>
> >> --
> >> 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.
> >> ---
> >> You received this message because you are subscribed to the Google Groups
> >> "sqlalchemy" group.
> >> To unsubscribe from this group and stop receiving emails from it, send an
> >> email to sqlalchemy+unsubscr...@googlegroups.com.
> >> To view this discussion on the web visit
> >> https://groups.google.com/d/msgid/sqlalchemy/ema56ad245-cad9-4096-8c55-9d75e8d52ea2%40textors-01.
> >
> >--
> >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.
> >---
> >You received this message because you are subscribed to the Google Groups
> >"sqlalchemy" group.
> >To unsubscribe from this group and stop receiving emails from it, send an
> >email to sqlalchemy+unsubscr...@googlegroups.com.
> >To view this discussion on the web visit
> >https://groups.google.com/d/msgid/sqlalchemy/CAFHwexeCQd6%2B5-O%3D1H8J8Zmfrg8vDsPmHjLg4PFY9RTySNdJ3w%40mail.gmail.com.
>
> --
> 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.
> ---
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sqlalchemy+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/emf25854f8-548b-4e38-86ce-a540a476e6c3%40textors-01.
--
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.
---
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sqlalchemy/CAFHwexd_GyPiPs2u1TWmfBb7%3Doab9tS7_4JQoT9Nnq_AgUK%3DuA%40mail.gmail.com.
