ticket 1480 is added for this issue which includes a patch to repair the
immediate test case. It does not yet cover the case where the column
expression takes the parent table into account.
bojanb wrote:
>
> Hello,
>
> It took me a couple of days to narrow this down. It appears that when
> object inherits from another object via joined table inheritance (I
> haven't tested the other two inheritance modes), mapped attributes
> defined as SQL expressions don't load correctly.
>
> In the example below I have a Party object, which can be a Person or a
> Company. The Person object has a mapped attribute "full_name", which
> is simply first and last name concatenated with the space (similar to
> the example in SQLALchemy documentation). Querying on Party and then
> accessing this property returns None. Strangely, if we queried on
> Person during the same session, subsequent query on Party would work.
>
> I've attached a fully self-contained test case below; just replace
> DB_URI with the correct value for you and the bug can be reproduced by
> executing the code.
>
> My setup:
> Python 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit
> (Intel)] on win32
> SQLAlchemy 0.5.5
>
> <code>
>
> from sqlalchemy import create_engine, Table, Column, Integer, String,
> MetaData, ForeignKey
> from sqlalchemy.orm import mapper, relation, backref, column_property,
> sessionmaker
> from sqlalchemy.sql import select, func
>
> DB_URI='postgres://postg...@localhost/postgres' #Replace this
> accordingly
> db_engine=create_engine(DB_URI, echo=True)
> metadata = MetaData()
>
> parties=Table('parties', metadata,
> Column('id', Integer, primary_key=True),
> Column('type', String(1), nullable=False) #This field
> needed for joined table inheritance
> )
>
> class Party(object):
> pass
>
> persons=Table('persons', metadata,
> Column('id', Integer, ForeignKey('parties.id'),
> primary_key=True), #Foreign key needed for joined table inheritance
> Column('first_name', String(50)),
> Column('last_name', String(50))
> )
>
> class Person(Party):
> def __init__(self, first_name, last_name):
> self.first_name=first_name
> self.last_name=last_name
>
> companies=Table('companies', metadata,
> Column('id', Integer, ForeignKey('parties.id'),
> primary_key=True),
> Column('name', String(50)),
> Column('tax_id', String(10))
> )
>
> class Company(Party):
> def __init__(self, name, tax_id):
> self.name=name
> self.tax_id=tax_id
>
> mapper(Party, parties, polymorphic_on=parties.c.type,
> polymorphic_identity='T')
> mapper(Person, persons, inherits=Party, polymorphic_identity='P',
> properties={
> 'full_name': column_property((persons.c.first_name + ' ' +
> persons.c.last_name).label('full_name'))
> })
> mapper(Company, companies, inherits=Party, polymorphic_identity='C')
>
> if __name__ == '__main__':
> metadata.create_all(db_engine)
> s=sessionmaker(bind=db_engine)()
> s.add_all([Person('John', 'Smith'), Company('ACME Inc.', '1234')])
> s.commit()
> try:
> #Weird - if the following two lines were run before the
> subsequent query, final assert wouldn't fail!!
> #all_persons=s.query(Person).all()
> #assert all_persons[0].full_name=='John Smith'
>
> all_parties=s.query(Party).all()
> #Altough we queried on Party, SQLAlchemy correctly recognizes
> that second object is a copmany, as per specification
> assert all_parties[1].tax_id=='1234'
> #However, for SQL expression mapped atributes it returns None
> instead of the stored value.
> #SQLAlchemy documentation clearly states that this should work
> - see section "Controlling Which Tables are Queried".
> #BTW, this failure doesn't happen for objects that are not
> part of inheritance hierarchy.
> assert all_parties[0].full_name=='John Smith'
> finally:
> s.close()
> metadata.drop_all(db_engine)
>
> </code>
>
> >
>
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~----------~----~----~----~------~----~------~--~---
