[sqlalchemy] sqlalchemy.exc.ArgumentError: Could not determine join condition between parent/child tables

[jo]

Hi all,
I don't know how to fix this error in my model:
sqlalchemy.exc.ArgumentError: Could not determine join condition between 
parent/child tables on relationship RuoloPermesso.permessi.  Specify a 
'primaryjoin' expression.  If 'secondary' is present, 'secondaryjoin' is 
needed as well.


    tbl['ruolo'] = Table('ruolo', database.metadata,
        Column('codice', Unicode(10), nullable=False, primary_key=True),
        Column('descrizione', Unicode(200), nullable=False),
        )

   tbl['permesso'] = Table('permesso', database.metadata,
       Column('id', Integer, Sequence('permesso_seq'),  
primary_key=True, nullable=False),
       Column('cod_menu', Unicode(10), ForeignKey('menu.codice'), 
nullable=False),
       Column('sub_menu', Unicode(10)),
       Column('codice', Unicode(200), nullable=False),
       Column('descrizione', Unicode(200), nullable=False),
       Column('path', Unicode(200), nullable=False),
       )

   tbl['ruolo_permesso'] = Table('ruolo_permesso', database.metadata,
       Column('cod_ruolo', Unicode(10), primary_key=True),
       Column('cod_permesso', Unicode(200), primary_key=True),
       Column('lettura', Boolean),
       Column('modifica', Boolean),
       Column('inserimento', Boolean),
       Column('cancellazione', Boolean),
       ForeignKeyConstraint(['cod_ruolo'], ['ruolo.codice']),
       ForeignKeyConstraint(['cod_permesso'], ['permesso.codice'], 
ondelete='CASCADE')
       )

mapper(Ruolo,
      tbl['ruolo'],
      column_prefix = 'ruolo_',
      properties = {
          'permissions' : relation(Permesso, 
secondary=tbl['ruolo_permesso'], backref='groups'),
      }
   )

mapper(Permesso,
      tbl['permesso'],
      column_prefix = 'permesso_',
   )
mapper(RuoloPermesso,
      tbl['ruolo_permesso'],
      column_prefix = 'ruolo_permesso_',
      properties = {
              'permessi' : relation(Permesso),
      }
   )

thanks for any help.
j

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