Two part question... I have a table of activity types . I want to
follow a ‘singleton pattern’ (ie. Only one instance of
‘run’,’jump’,’swim’ etc.). I have a get_or_create function on the
class that works as long as programmers using my module call:
session.add( ActivityType.get_or_create(‘fly’))
session.commit()
Question1: How can I modify my model/class shown below to either
prevent, or better yet, allow:
session.add(ActivityType(‘fly’))
session.commit()
Question2: (depending on answer above.) How can I ensure singleton if
my programmers do:
a1 = ActivityType(‘fly’)
a2 = ActivityType(‘fly’)
session.add(a1)
session.add(a2)
session.commit()
Thanks or any guidance.
Rich
# Here is my table + class + mapper
tblActivityType = sa.Table('activitytype', metadata,
sa.Column('id', sa.Integer, primary_key=True),
sa.Column('name', sa.String(128), nullable=False)
)
class ActivityType(object):
def __init__(self, name=None):
self.name = name.lower()
@staticmethod
def get_or_create(tmpStr):
_session = Session()
mything =
_session.query(ActivityType).filter_by(name=tmpStr.lower() ).first()
if mything is not None:
return mything
else:
return ActivityType(tmpStr.lower())
mapper(ActivityType, tblActivityType)
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