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
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SQLAlchemy -
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http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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