Class expression and PostGIS

[Paul Ramsey]

Try

EXPRESSION ('[object_type]' eq 'agents')

"=" is a numeric comparison, and you want a string comparison.  The  
extra '' around the attribute name also seem to help clarify things  
for the expression parser.

On 23-Jun-06, at 4:10 PM, Nigel Gilbert wrote:

> [Many thanks to those who helped me yesterday overcome a problem with
> creating an oid index, now solved as a result of their advice]
>
> I have a PostGIS database including a table, world, with columns,
> object_type (containing either one of the strings, 'plants' or  
> 'agents') and
> 'geom', containing points.  In my map file I have:
>
> LAYER
>     NAME World
>     CONNECTIONTYPE    postgis
>     CONNECTION    "user=..... dbname=...."
>     DATA                "geom from world"
>     STATUS            ON
>     TYPE                POINT
>
>     CLASS
>         NAME            Agents
>         EXPRESSION    ([object_type] = 'agents')
>         STYLE
>             COLOR        255 111 207    # pink
>         END
>     END
>
>     CLASS
>         NAME            Plants
>         EXPRESSION ([object_type] = 'plants')
>         STYLE
>             COLOR        0 128 64        # green
>         END
>     END
> END
>
> This gives a map displaying nothing, although if I comment out the
> expressions, I get the points I would then expect.  In other words,  
> the
> expressions are always returning false.  But getting the data  
> directly:
>
>  select object_type, AsText(geom) from world limit 3;
>                                              object_type
> |     astext
> ---------------------------------------------------------------------- 
> ------
> --------------------------+----------------
>  plants
> | POINT(13 19)
>  plants
> | POINT(228 840)
>  plants
> | POINT(694 674)
> (3 rows)
>
> is fine.  What's wrong??
>
> Thanks again!
>
> Nigel