Mike,
Michael Bayer wrote:
> On Nov 7, 2007, at 10:23 AM, Werner F. Bruhin wrote:
>
>
>> How can I define a column in the table as read-only?
>>
>> I have some "computed by" columns, e.g.:
>> consumedvalue computed by (quantity*unitprice)
>>
>> These columns can not be updated, otherwise I get the following
>> exception:
>> ProgrammingError: (ProgrammingError) (-151, 'isc_dsql_prepare: \n
>> attempted update of read-only column')
>>
>>
>
> read-only behavior is a class-level thing, so something like this:
>
> class MyClass(object):
> def mycol(self):
> return self._mycol
> mycol = property(mycol)
>
> mapper(MyClass, mytable, properties={
> '_mycol':mytable.c.mycol,
> 'mycol':synonym('_mycol')
> })
>
>
> Theres a ticket in trac which will make the above configuration
> slightly less verbose in a future release.
>
I don't have many of these, so no big deal that it is verbose.
However I must not do something wrong in transposing the above as I
still get the error.
I must be a bit dense on this, here is what I have done:
consumption_table = sa.Table(u'consumption', metadata,
sa.Column(u'consumptionid', sa.Integer(),
sa.Sequence('gen_consumption_consumptionid'), primary_key=True,
nullable=False),
sa.Column(u'quantity', sa.Integer()),
sa.Column(u'unitprice',
sa.Numeric(precision=18,length=2,asdecimal=True)),
sa.Column(u'consumedvalue',
sa.Numeric(precision=18,length=2,asdecimal=True)),
....
)
class Consumption(object):
def consumedvalue(self):
return self._consumedvalue
consumedvalue = property(consumedvalue)
pass
consumption = sao.mapper(Consumption, consumption_table,
properties={
...
'cellar': sao.relation(Cellar, backref='consumption'),
'_consumedvalue': consumption_table.c.consumedvalue,
'consumedvalue': sao.synonym('_consumedvalue'),
})
Can you point out what I did wrong, please.
Werner
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