On Mon, Oct 3, 2016 at 11:43 AM, Jinghui Niu <[email protected]> wrote:
> This really helps. Thank you Simon! I still have a couple of smaller
> questions.
>
>> When you access <class>.fullname, the "self" parameter is now the
>> *class*, so self.firstname and self.lastname are SQLAlchemy column
>> properties.
>
>
> Here by *column properties* do you mean the object returned by
> column_property() function? Are they used interchangeably with
> *InstrumentedAttribute object*?
>
In this case they are in fact InstrumentedAttributes. (Actually, I
think properties created using column_property are *also*
InstrumentedAttributes).
>
>> but you'll need to accept that you can't simply use your
>> currency_exchange_rate_lookup
>> dictionary as it is.
>
>
> I have a dream, that one day SQL side and Python side can truly mingle in
> such a way that when you query SQL you can directly refer to variables
> defined in the Python model class:-)
>
In your case, I guess you need to construct some sort of case
statement based on the values in the dictionary. Here's some untested
code:
@amountInCAD.expression
def amountInCAD(cls):
conditions = []
rates = cls.currency_exchange_rate_lookup.items()
for ((from_currency, to_currency), exchange_rate) in rates:
assert to_currency == 'CAD'
conditions.append((cls.currency == from_currency), cls.amount
* exchange_rate))
# You'll need to implement the "ELSE" case yourself
return sa.case(conditions)
Hope that helps,
Simon
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