Le vendredi 15 juin 2012 12:00:28 UTC+2, Thierry Florac a écrit :
>
> Hi,
>
> I'm using SQLAlchemy (0.7.4) with GeoAlchemy to map tables containing
> geographic entities from a PostgreSQL/PostGIS database.
>
> As I have to handle data from several parts of the world, each part using
> it's own geographic projection, my testing model which I'll try to describe
> is based on:
> - a parent class ("TestIMG"), containing common attributes and a shape in
> "world-wide" WGS84 coordinates system
> - for each projection system, a child class, inheriting from TestIMG and
> containing only the shapes in the given projection system.
> TestIMG can be seen as an abstract class; discrimination between child
> classes is based on a common "SRID" attribute.
>
> I've mapped my classes as follow:
>
> class TestIMG(Base):
> __tablename__ = 'test_img'
> id = Column('id', Integer, primary_key=True)
> data = Column('data', Unicode(20))
> wgs_shape = GeometryColumn('wgs_shape', Point(srid=4326))
> srid = Column('srid', Integer)
> __mapper_args__ = { 'concrete': False,
> 'polymorphic_on': srid }
>
> class TestIMG_france(TestIMG):
> __tablename__ = 'test_img_france'
> __mapper_args__ = { 'polymorphic_identity': 2154,
> 'concrete': True }
> id = Column('id', Integer, ForeignKey(TestIMG.id), primary_key=True)
> shape = GeometryColumn('shape', Point(srid=2154))
>
> class TestIMG_guyane(TestIMG):
> __tablename__ = 'test_img_guyane'
> __mapper_args__ = { 'polymorphic_identity': 32622,
> 'concrete': True }
> id = Column('id', Integer, ForeignKey(TestIMG.id), primary_key=True)
> shape = GeometryColumn('shape', Point(srid=32622))
>
> TestIMG_union = polymorphic_union({ 'test_img_france':
> TestIMG_france.__table__,
> 'test_img_guyane':
> TestIMG_guyane.__table__ },
> 'projection', 'test_img')
>
>
> When I make a query in a child class, everything is OK; but when I try to
> query the main class, I get an error:
>
> >>> session.query(TestIMG).all()
>
> Traceback (most recent call last):
> File "<console>", line 1, in <module>
> File
> "/var/local/eggs/SQLAlchemy-0.7.4-py2.7-linux-x86_64.egg/sqlalchemy/orm/query.py",
>
> line 1947, in all
> return list(self)
> File
> "/var/local/eggs/SQLAlchemy-0.7.4-py2.7-linux-x86_64.egg/sqlalchemy/orm/query.py",
>
> line 2178, in instances
> rows = [process[0](row, None) for row in fetch]
> File
> "/var/local/eggs/SQLAlchemy-0.7.4-py2.7-linux-x86_64.egg/sqlalchemy/orm/mapper.py",
>
> line 2614, in _instance
> return _instance(row, result)
> File
> "/var/local/eggs/SQLAlchemy-0.7.4-py2.7-linux-x86_64.egg/sqlalchemy/orm/mapper.py",
>
> line 2627, in _instance
> tuple([row[column] for column in pk_cols])
> File
> "/var/local/eggs/SQLAlchemy-0.7.4-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py",
>
> line 2654, in _key_fallback
> expression._string_or_unprintable(key))
> NoSuchColumnError: "Could not locate column in row for column '
> test_img_france.id'"
>
>
> I've tried to test several configurations but everything fails until now.
> I'll also add that I **have to** use declarative form of SQLAlchemy,
> because GeoAlchemy doesn't seem to handle anything else :-/
>
> Any help would be greatly welcome !
>
> Best regards,
> Thierry
>
Hum, hum...!
In fact, it finally works, just by removing "concrete" argument from child
classes mapper args...
Sorry for the noise :-/
Regards,
Thierry
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