I'm trying to use types.TypeDecorator to define a set of strings
stored in the database as a csv list, where the empty set is stored as
null. process_bind_param seems to work, as values set on the bound
field seem to get entered correctly; but process_result_value never
seems to be called when reading that field, or when loading an
instance from the database.
What am I doing wrong? (I'm using 0.4.2p3)
class StringSet (types.TypeDecorator):
"""A type that receives an iterable of strings, and returns a set
of those strings.
Stored in the database as a csv list of strings.
"""
impl = types.String
def process_bind_param (self, value, engine):
if not value:
return None
else:
return ",".join(set(value))
def process_result_value (self, value, engine):
if not value:
return set()
else:
return set(value.split(","))
def copy (self):
return StringSet(self.impl.length)
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