join object in mapscript

[Stephen Woodbridge]

Sean Gillies wrote:
> On Jun 29, 2005, at 3:31 AM, Klement Szabolcs wrote:
> 
>> I want use join object from mapscipt (java). Why this is not exists in
>> mapscript wrapper? and when to make this? I think this is a very 
>> important
>> feature for real time cartogram, thematic map, or for other spatial 
>> analisys.
>>
> 
> Actually, since joined data is only accessible within a query, it is not 
> important for cartography. We cannot classify or filter based on a join.
> 
> Mapscript lacks a join object because no one has needed it or asked for 
> it. It is very simple to instead use one of your language's data 
> connectors (jdbc or xbase) and join the data within your application. 
> With mapscript you are also not limited to joins on a DBF, and can bring 
> in data from practically any database.

I would add to Sean's comments here that you can do joins for thematic 
mapping with mapserver, but they are only done via the DATA "..." 
statement and are being processed outside of mapserver. For example when 
using PostGIS or GDAL/OGR. A join object would only be useful in the 
query mode as Sean points out, you you need to think about doing 
thematic mapping in terms of the DATA source provider.

I have wanted mapserver to handle joins for classification for a long 
time, but have just recently started using PostGIS to get the capability 
and I'm very happy with the functionality there and the integration with 
mapserver.

-Steve W.