I probably wouldn't use this:
if test_type == ChildClass1().typ_id:
...simply because creating an instance of the object just to get
access to the typ_id seems like a waste of effort. If you really need
to check integer typ_id values, the staticmethod approach seems fine.
Simon
On Mon, Apr 12, 2021 at 8:58 PM 'Sören Textor' via sqlalchemy
<sqlalchemy@googlegroups.com> wrote:
>
> Hi Simon
> Again you really helped me out. I don't know what point I missed, but
> now it works. As usual it's not as simpe le or lets say there are a lot
> more code pieces to change before I can really test it in my code. But I
> got it.
>
> just one more thing:
> I often have to check if a given tpye t the class type. Therefore I
> usally use the statci method.
>
> Thus what would you do:
>
> if test_type == ChildClass1().typ_id:
> or
> if test_type==ChildClass.TypID():
>
> and to ensure only TypId exists fpr that type:
> __mapper_args__ = {
> "polymorphic_identity": ChildClass.TypID(),
> }
>
> And as I said: Thanks a lot!
>
> SirAnn
>
>
> ------ Originalnachricht ------
> Von: "Simon King" <si...@simonking.org.uk>
> An: sqlalchemy@googlegroups.com
> Gesendet: 12.04.2021 20:26:48
> Betreff: Re: Re[2]: [sqlalchemy] Invertinace mapped type_id to fix value
> for each child class
>
> >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.
> >> >> ---
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> >> 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.
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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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> >
> >--
> >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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--
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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