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+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sqlalchemy/b08ba9e6-e1e3-451e-b39b-bc5ee4b63847n%40googlegroups.com.
