Yoann Roman wrote:
> Given the following relationships:
>
> employees_table = Table('employees', metadata,
> Column('id', Integer, primary_key=True),
> Column('row_type', Integer, nullable=False)
> Column('name', String(50)),
> Column('is_certified', Boolean)
> )
>
> employee_mapper = mapper(Employee, employees_table,
> polymorphic_on=employees_table.c.row_type,
> polymorphic_identity=1,
> exclude_properties=['is_certified'])
> manager_mapper = mapper(Manager, inherits=employee_mapper,
> polymorphic_identity=2,
> properties={
> 'is_certified': employees_table.c.is_certified
> })
>
> How can I query for employees who aren't managers or managers who are
> certified without referring to the polymorphic identity? Basically,
> without doing this:
>
> session.query(Employee).filter(or_(Employee.row_type!=2,
> Manager.is_certified==True))
the ultimate SQL must include the "row_type" column, or perhaps you could
detect if "is_certified" is NULL to detect a non-manager row. There's no
way to get around having to tell your query "check the type of the object"
somehow.
However, if you're just disturbed about the actual "row_type" column and
the hardcoding of "2", you can make yourself an operator pretty easily
here. A simple one is like:
def isinstance_(cls_):
mapper = class_mapper(cls_)
return mapper.polymorphic_on == mapper.polymorphic_identity
a more comprehensive one that takes into account further subclasses:
def isinstance_(cls_):
mapper = class_mapper(cls_)
return mapper.polymorphic_on.in_(
[m.polymorphic_identity
for m in mapper.polymorphic_iterator()]
)
a query like:
sess.query(Employee).filter(~isinstance_(Manager))
would render:
SELECT *
FROM employees
WHERE employees.row_type NOT IN (...)
>
> Thanks!
>
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