On Aug 24, 2010, at 11:03 AM, Frank wrote:
> Hello,
>
> I am trying to reflect the example from
> http://hg.sqlalchemy.org/sqlalchemy/file/04c17c7d88d6/examples/association/basic_association.py
> but with my own data structures.
>
> I want to manage nutrients, nutrient values and nutrition lists.
> Therefore I have created a custom data type "weight" which helps me
> doing calculations with weights in different units. The relation
> between nutrients and nutrition lists is m:n, one list can have many
> nutrients and nutrients can be in many lists. The association table
> (nutrition values) stores the amount of a nutrient associated to one
> list. I think I got things working mostly, but flushing my data to the
> database breaks the program:
> http://paste.pocoo.org/show/253961/
>
> From what I understand from the message, there seems to be a problem
> with my custom data type. Maybe someone with more skill in sqlalchemy
> than me can shed some light on the matter ...
>
> Here's the full script
>
> http://paste.pocoo.org/show/253956/
the TypeDecorator just needs to handle the case where the bind or result value
is None:
class WeightType(types.TypeDecorator):
impl = types.Numeric
def process_bind_param(self, weight, dialect):
if weight is None:
return None
return weight.base_value
def process_result_value(self, value, dialect):
if value is None:
return None
return Weight(value, "g")
script runs fine after that. You probably meant to name the "nutrient_weight"
column as "weight", or otherwise remap the attribute on the NutritionValue
class mapper with that name.
>
> Many thanks
>
> Frank
>
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