For reference I have attached a complete test case including a copy of the GUID code from the documentation.
On May 6, 2013, at 23:22, Wichert Akkerman <wich...@wiggy.net> wrote: > I was looking at using a UUID as primary key for a table. Using the > backend-agnostic GUID type from > http://docs.sqlalchemy.org/en/rel_0_8/core/types.html#backend-agnostic-guid-type > I get strange behaviour though. I whipped up a simple test case: > > > class Data(BaseObject): > __tablename__ = 'data' > uuid = Column(GUID(), primary_key=True) > > > metadata.create_all() > session = sessionmaker(autocommit=False)() > > uuid = 'ac4daeff-3af3-4b83-b8c7-3aa34e34151c' > obj = Data(uuid=uuid) > session.add(obj) > assert session.query(Data).get(uuid) is obj > assert session.query(Data).filter(Data.uuid == uuid).first() is obj > > Both asserts fail when I do this. The problem appears to be conversion from > to a uuid.UUID instance in GUID.process_result_value: this always creates a > new UUID instance, which probably causes a miss when SQLAlchemy tries to find > an instance in its identify map. > > Is this a bug in the GUID example in the documentation, or is this something > that can be improved in the identity map? > > Wichert.
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On May 6, 2013, at 23:22, Wichert Akkerman <wich...@wiggy.net> wrote:
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from uuid import UUID
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.dialects import postgresql
metadata = MetaData(bind=create_engine('sqlite://'))
BaseObject = declarative_base(metadata=metadata)
class GUID(TypeDecorator):
"""Platform-independent GUID type.
Uses Postgresql's UUID type, otherwise uses CHAR(36), storing as
stringified hex values.
This implementation is based on the SQLAlchemy
`backend-agnostic GUID Type
<http://www.sqlalchemy.org/docs/core/types.html#backend-agnostic-guid-type>`_
example.
"""
impl = CHAR
def load_dialect_impl(self, dialect):
if dialect.name == 'postgresql':
return dialect.type_descriptor(postgresql.UUID())
else:
return dialect.type_descriptor(CHAR(36))
def process_bind_param(self, value, dialect):
if value is None:
return value
elif dialect.name == 'postgresql':
return str(value)
else:
if not isinstance(value, UUID):
return str(UUID(value))
else:
# hexstring
return str(value)
def process_result_value(self, value, dialect):
if value is None:
return value
else:
return UUID(value)
class Data(BaseObject):
__tablename__ = 'data'
uuid = Column(GUID(), primary_key=True)
metadata.create_all()
session = sessionmaker(autocommit=False)()
uuid = 'ac4daeff-3af3-4b83-b8c7-3aa34e34151c'
obj = Data(uuid=uuid)
session.add(obj)
assert session.query(Data).get(uuid) is obj
assert session.query(Data).filter(Data.uuid == uuid).first() is obj
