Re: [sqlalchemy] Inherited abstract model with relationship causing "Cannot compile Column object until its 'name' is assigned."

[Mike Bayer]

On 08/30/2016 01:54 PM, TomS. wrote:
Hi,

I would like to create an abstract model which should be inherited.
Unfortunately, I am not allowed to used Foreign Keys, this is the reason
why I introduced work around via relationship. Here is the whole code:

class DepTest(db.Model):

    __tablename__ = u'deptest'
    __bind_key__ = u'section'

    department_pk_id = db.Column(db.Integer, primary_key=True)
    department_id = db.Column(db.Integer)
    department_name = db.Column(db.String(1000))


class PPLTest(db.Model):

    __abstract__ = True

    person_pk_id = db.Column(db.Integer, primary_key=True)
    person_name = db.Column(db.String(1000))
    person_surname = db.Column(db.String(1000))
    department_id = db.Column(db.Integer)

    @hybrid_property
    def person_name_surname(self):
        return self.person_name + u' ' + self.person_surname


class Level1(PPLTest):

    __tablename__ = u'ppl_level1'
    __bind_key__ = u'section'

    department = relationship(
        DepTest,
        primaryjoin=remote(DepTest.department_id) == foreign(
            PPLTest.department_id))


But I get "Cannot compile Column object until its 'name' is assigned."

So I defined department (in Level1) using @declared_attr:

    def department(clss):
        return relationship(DepTest,
                            primaryjoin=lambda:
remote(DepTest.department_id) == foreign(
                                clss.department_id)
                            )

and now it works as expected. The question is - is it defined properly,
or I should be aware of sth?

Yes, using a lambda here, or alternatively using a string-eval, is a 
good way to defer evaluation of that primaryjoin until declarative has 
set things up and put names in your Column objects.

Just curious to see the stack trace here because I don't see where the 
Column needs to actually be compiled into a string.





Thank you for any suggestions!

Cheers


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