yeah I am not a huge fan of declared_attr.cascading except for maybe a table name convention
On Sun, Nov 28, 2021, at 11:38 PM, niuji...@gmail.com wrote: > Thanks for pointing this out. It did address this problem already. > I just solved this by manually adding all the primary/foreign keys to each > classes. Not a big deal, actually it helps clear code! > On Sunday, November 28, 2021 at 6:37:30 PM UTC-8 Mike Bayer wrote: >> __ >> this is addressed in the docs which discuss "cascading" here: >> >> https://docs.sqlalchemy.org/en/14/orm/declarative_mixins.html#mixing-in-columns-in-inheritance-scenarios >> >> "The `declared_attr.cascading` feature currently does *not* allow for a >> subclass to override the attribute with a different function or value. This >> is a current limitation in the mechanics of how `@declared_attr` is >> resolved, and a warning is emitted if this condition is detected. This >> limitation does *not* exist for the special attribute names such as >> `__tablename__`, which resolve in a different way internally than that of >> `declared_attr.cascading`." >> >> >> you will see a warning in your program's output: >> >> SAWarning: Attribute 'record_id' on class <class '__main__.Programmer'> >> cannot be processed due to @declared_attr.cascading; skipping >> >> >> as a workaround, you can look for the attribute in __dict__ and return it, >> though you still get the warning: >> >> class has_polymorphic_id(object): >> @declared_attr.cascading >> def record_id(cls): >> if "record_id" in cls.__dict__: >> return cls.__dict__['record_id'] >> elif has_inherited_table(cls): >> return Column(ForeignKey("employee.record_id"), >> primary_key=True) >> else: >> return Column(Integer, primary_key=True) >> >> >> otherwise you'd want to look at "cls" with inspect(cls).local_table etc. and >> figure out the correct column to include in the FK if you are doing things >> this way. >> >> >> >> >> >> >> >> On Sun, Nov 28, 2021, at 4:22 PM, niuji...@gmail.com wrote: >>> I've just manually put this line to the `Programmer` class definition, but >>> it still gives me the same error, strangely: >>> >>> >>> class Programmer(Engineer): >>> __tablename__ = 'programmer' >>> record_id = Column(ForeignKey('engineer.record_id'), >>> primary_key=True) >>> .... >>> On Sunday, November 28, 2021 at 8:25:30 AM UTC-8 Mike Bayer wrote: >>>> >>>> >>>> On Sun, Nov 28, 2021, at 4:24 AM, niuji...@gmail.com wrote: >>>>> I'm using the "joined table inheritance" model. I have three levels of >>>>> inheritance. >>>>> >>>>> class has_polymorphic_id(object): >>>>> @declared_attr.cascading >>>>> def record_id(cls): >>>>> if has_inherited_table(cls): >>>>> return Column(ForeignKey('employee.record_id'), >>>>> primary_key=True) >>>>> else: >>>>> return Column(Integer, primary_key=True) >>>>> >>>>> >>>>> class Employee(has_polymorphic_id, Base): >>>>> __tablename__ = 'employee' >>>>> name = Column(String(50)) >>>>> type = Column(String(50)) >>>>> >>>>> __mapper_args__ = { >>>>> 'polymorphic_identity':'employee', >>>>> 'polymorphic_on':type >>>>> } >>>>> >>>>> class Engineer(Employee): >>>>> __tablename__ = 'engineer' >>>>> .... >>>>> >>>>> class Programmer(Engineer): >>>>> __tablename__ = 'programmer' >>>>> .... >>>>> >>>>> This only works for the second level, namely `Enginner` can inherits the >>>>> foreignkey/primarykey from `Employee`'s mixin, but the next level, the >>>>> `Programmer`, python gives me an error: >>>>> `sqlalchemy.exc.NoForeignKeysError: Can't find any foreign key >>>>> relationships between 'engineer' and 'programmer'.` >>>> >>>> The "cascading" attribute seems to be working correctly. The error here >>>> is because you aren't providing any column that will allow for a JOIN >>>> between the "programmer" and "engineer" table. >>>> >>>> you would want Programmer.record_id to be a foreign key to >>>> Engineer.record_id, not Employee.record_id. When you load Programmer >>>> rows, the join would be "FROM employee JOIN engineer ON <onclause> JOIN >>>> programmer ON <onclause>". >>>> >>>> >>>>> >>>>> Is this designed this way? And if I manually set the foreignkey, should >>>>> the third level reference to the base level or to its immediate parent >>>>> level's primarykey? >>>> >>>> it has to be to the immediate parent. that's what the error message here >>>> is talking about. >>>> >>>> >>>> >>>>> >>>>> >>>>> -- >>>>> 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+...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/sqlalchemy/02ce8134-2946-4d1b-b6d3-e47ad7944e0en%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/sqlalchemy/02ce8134-2946-4d1b-b6d3-e47ad7944e0en%40googlegroups.com?utm_medium=email&utm_source=footer>. >>>> >>> >>> >>> -- >>> 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+...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/sqlalchemy/b08ba9e6-e1e3-451e-b39b-bc5ee4b63847n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/sqlalchemy/b08ba9e6-e1e3-451e-b39b-bc5ee4b63847n%40googlegroups.com?utm_medium=email&utm_source=footer>. >> > > > -- > 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/dfeef924-d1c9-483d-b293-5431cd0940ben%40googlegroups.com > > <https://groups.google.com/d/msgid/sqlalchemy/dfeef924-d1c9-483d-b293-5431cd0940ben%40googlegroups.com?utm_medium=email&utm_source=footer>. -- 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. 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