On Jun 30, 1:24 pm, Michael Bayer <[EMAIL PROTECTED]> wrote:
> On Jun 30, 2008, at 1:04 PM, Hans wrote:
>
>
>
> > The problem is that I'd like to have sqlalchemy return KML for all
> > geometry types by default, but I don't know how to setup my type to
> > specify a SQL function that needs to be applied to the column in the
> > select clause. Is this possible? Alternatively, it would be
> > *perfect* to have additional *_kml properties added to the result
> > objects (one for each GEOMETRY column), but this seems even more
> > complex (?).
>
> > I was expecting my convert_result_value method to operate on the SQL,
> > but I am assuming from looking at the generated SQL that this method
> > is actually going to operate on the raw data that was returned from
> > SQL. So, is there a way to accomplish what I want?
>
> TypeEngine currently has no hook that's consulted during SQL
> rendering, which is where you're looking for this to happen. Its
> not impossible to add such a feature but its not yet clear to me that
> TypeEngine is the appropriate place for this decision to be made.
> Its also not apparent yet how specifically within the SQL it would be
> appropriate to render the function, and how labeling would work -
> since SQLA, when it generates nested select statements, uses labels to
> track each column named against a table outwards...such as "select
> foo, bar from (select a as foo, b as bar from table)". In the case of
> a SQL function, the column name becomes somewhat undefined until a
> label is applied. SQLA nests SELECT statements very often.
>
> You might want to try experimenting with a simple monkeypatch approach
> just to see what kind of results you get - this is just a guess based
> on a particular compiler hook we have that specifically processes
> columns being rendered within a select:
>
> from sqlalchemy.databases.postgres import PGCompiler
>
> def label_select_column(self, select, column, asfrom):
> if isinstance(col.type, MyGISType):
> return func.some_kml_function(col).label(column.name)
> else:
> return super(self, PGCompiler).label_select_column(select,
> column,
> asfrom)
>
> PGCompiler.label_select_column = label_select_column
>
> if the above leads to decent results we can attempt to add a hook onto
> TypeEngine perhaps.
Thank you -- I will give that a shot!
Hans
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