oh. yeah it's going to have to not do that. try out tip, it will only put
the type expression on those columns being delivered to the result (i.e. the
outermost).
On Sep 3, 2012, at 9:41 AM, Eric Lemoine wrote:
> Hi
>
> I'm facing another column_expression issue. It is not related to the
> previous issue, and I'm sure if SQLAlchemy can help me with this one.
>
> ----
> from sqlalchemy.types import UserDefinedType
> from sqlalchemy.sql import func
>
>
> class Geometry(UserDefinedType):
>
> def column_expression(self, col):
> return func.ST_AsBinary(col, type_=self)
>
>
> from sqlalchemy import Table, Column, MetaData
>
> lakes = Table('lake', MetaData(),
> Column('geom', Geometry)
> )
>
> from sqlalchemy.sql.expression import select, alias
> s = select([lakes])
> a = alias(s, 'name')
> s = a.select()
> print s
> ----
>
>
> The print statement returns this:
>
>
> SELECT ST_AsBinary(name.geom) AS geom FROM (SELECT
> ST_AsBinary(lake.geom) AS geom FROM lake) AS name
>
>
> Which is expected. But the execution of this statement fails in my
> PostGIS database, because ST_AsBinary cannot receive a bytea value as
> input. (the outer ST_AsBinary call receives what's returned from the
> inner ST_AsBinary call). It would work if ST_AsBinary was idempotent,
> but it's not in PostGIS 2
> (<http://trac.osgeo.org/postgis/ticket/1869>).
>
> I'm stuck on this one.
>
>
> --
> Eric Lemoine
>
> Camptocamp France SAS
> Savoie Technolac, BP 352
> 73377 Le Bourget du Lac, Cedex
>
> Tel : 00 33 4 79 44 44 96
> Mail : eric.lemo...@camptocamp.com
> http://www.camptocamp.com
>
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