Behaviour of WFS filter query

Yewondwossen Assefa assefa at DMSOLUTIONS.CA
Wed Feb 15 19:12:50 EST 2006


What happens in this case is the the <Filter> is transformed into an SQL 
expression and set on the layer's filter element. Then a query is 
performed.  This happens for relativly simple filter expressions where 
it is possible to convert it to SQL expressions.

In any case, all the querying, filter transformation is always done on 
the server and only the resulting features are returned.

Later,



Hester Viola wrote:
> Hello,
> 
> This is a general question rather than an issue I am having.
> 
> I am wondering about the behaviour of MapServer in processing a WFS
> GetFeature requests, with a filter in the URL, reading data from PostGIS or
> ESRI shapefile.
> eg
> http://www4.bom.gov.au/cgi-bin/mapserver/mapserv?map=/web/htdocs/mapserver/weather.map&version=1.0.0&service=WFS&request=GetFeature&typename=metarrain&filter=<Filter><PropertyIsGreaterThan><PropertyName>rf9am</PropertyName><Literal>0.2</Literal></PropertyIsGreaterThan></Filter>
> 
> Does this sort of request :
> 1. Return all of the data in the layer to MapServer, which then applies the
> filter (meaning there is significant Internet traffic involved)
> 
> OR
> 
> 2. Generate an SQL query within MapServer in order to only request the data
> defined by the filter from the database or file (thereby reducing the
> Internet traffic)
> 
> I hope that this makes sense and someone can provide some information
> 
> Thanks in advance
> Hester


-- 
----------------------------------------------------------------
Assefa Yewondwossen
Software Analyst

Email: assefa at dmsolutions.ca
http://www.dmsolutions.ca/

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925
----------------------------------------------------------------



More information about the mapserver-users mailing list