On Feb 9, 2012, at 1:33 PM, Chris Withers wrote:
> On 09/02/2012 15:47, Chris Withers wrote:
>> My thinking was leaning towards actually abandoning the full declarative
>> base and coming up with a light weight one (or maybe even class
>> decorator) that basically added recorded the class in a sequence (much
>> like the declarative reflection does) and then calls
>> instrument_declarative with each class at the point of relfection.
OK I'm not sure if you are on 0.7.5 but the string name of the column is
accepted for "polymorphic_on". The recipe just needs to fill in the
'inherits' keyword within prepare(), and that's it. See below:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.orm.util import _is_mapped_class
from sqlalchemy.ext.declarative import declarative_base, declared_attr
class DeclarativeReflectedBase(object):
_mapper_args = []
@classmethod
def __mapper_cls__(cls, *args, **kw):
"""Declarative will use this function in lieu of
calling mapper() directly.
Collect each series of arguments and invoke
them when prepare() is called.
"""
cls._mapper_args.append((args, kw))
@classmethod
def prepare(cls, engine):
"""Reflect all the tables and map !"""
while cls._mapper_args:
args, kw = cls._mapper_args.pop(0)
klass = args[0]
# autoload Table, which is already
# present in the metadata. This
# will fill in db-loaded columns
# into the existing Table object.
if args[1] is not None:
table = args[1]
Table(table.name,
cls.metadata,
extend_existing=True,
autoload_replace=False,
autoload=True,
autoload_with=engine,
schema=table.schema)
for c in klass.__bases__:
if _is_mapped_class(c):
kw['inherits'] = c
break
klass.__mapper__ = mapper(*args, **kw)
Base = declarative_base()
class Reflected(DeclarativeReflectedBase, Base):
__abstract__ = True
class GeneralType(Reflected):
__tablename__ = 'single_inherits'
__mapper_args__ = dict(polymorphic_on='type')
class TypeOne(GeneralType):
__mapper_args__ = dict(polymorphic_identity='one')
class TypeTwo(GeneralType):
__mapper_args__ = dict(polymorphic_identity='two')
e = create_engine('sqlite://', echo=True)
e.execute("""
create table single_inherits(
id integer primary key,
type varchar(30)
)
""")
Reflected.prepare(e)
s = Session(e)
s.add_all([
TypeOne(type="one"), TypeOne(type="one"), TypeTwo(type="two")
])
s.commit()
s.close()
print s.query(GeneralType).all()
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