Re[2]: [sqlalchemy] Invertinace mapped type_id to fix value for each child class

Mon, 12 Apr 2021 10:40:44 -0700 

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

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