I am trying to generate tables/classes dynamically. The code below is
my latest attempt, but I cannot get it to work.
-------------------------------------------------------------
class TableName(object):
@declared_attr
def __tablename__(cls): return cls.__name__
class Inherit(object):
@declared_attr
def id(cls): #<= is not called for S
base = cls.__bases__[len(cls.__bases__) - 1]
print "class, base:", cls.__name__, base.__name__
return Column(Integer, ForeignKey(base.__name__ + '.id'),
primary_key = True)
@declared_attr
def __mapper_args__(cls):
return {'polymorphic_identity': cls.__name__}
class Object(Base, TableName):
association_tables = {}
id = Column(Integer, primary_key = True)
type_name = Column(String(50), nullable = False)
__mapper_args__ = {'polymorphic_on': type_name}
if __name__ == '__main__':
session = setup(engine)
T = type('T', (Inherit, Object), {'Tdata': Column(String(50))})
S = type('S', (T,), {'Sdata': Column(String(50))}) #<= Error
session.commit()
print S.__table__.c
-------------------------------------------------------------
the output is:
-------------------------------------------------------------
class, base: T Object
class, base: T Object
class, base: T Object
Traceback (most recent call last):
File "D:\Documents\Code\Eclipse\workspace\SQLAdata\src\test4.py",
line 55, in <module>
S = type('S', (T,), {'Sdata': Column(String(50))})
File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1336, in __init__
_as_declarative(cls, classname, cls.__dict__)
File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1329, in _as_declarative
**mapper_args)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\__init__.py",
line 1116, in mapper
return Mapper(class_, local_table, *args, **params)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
197, in __init__
self._configure_inheritance()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
473, in _configure_inheritance
self.local_table)
File "C:\Python27\lib\site-packages\sqlalchemy\sql\util.py", line
303, in join_condition
"between '%s' and '%s'.%s" % (a.description, b.description, hint))
sqlalchemy.exc.ArgumentError: Can't find any foreign key relationships
between 'T' and 'S'.
-------------------------------------------------------------
What is wrong with this approach. Is there a good way to approach this
problem (I have tried a couple already).
Also: Why is Inherit.id() called 3 times for T
Please help!
Lars
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