[mapserver-users] WFS Filter Encoding and resulting DB-queries

[Yewondwossen Assefa]

On 23/02/2011 8:06 AM, Stephan Holl wrote:
> Hello Assefa,
>
> Yewondwossen Assefa<yassefa at dmsolutions.ca>, [20110223 - 07:26:34]
>
>> Hi Stephan,
>>
>> On 22/02/2011 3:44 AM, Stephan Holl wrote:
>>> Hello list,
>>>
>>> while playing with MapServer WFS Filter Encoding capabilities I
>>> found some strange things when it comes to form the DB-queries (the
>>> requested layer is PostGIS-driven).
>>>
>>> It seems that there will always be a full table-scan and later on
>>> the FE will be applied. Is this done by design?
>>>
>>    Filters that do include spatial filters end up using the mapserver
>> experssions. 'Simple' filters should end be using traslated into the
>> layer's filter expression and end up being used by postgis as part of
>> the data selection. What does the filter encoding looks like?
> It is not a spatial-filter we use currently. It is an attribute-based
> IsLike-Filter like seen here[1], but we use it with POST. So adding a
> BBOX-related filter as another AND-filter will result in optimized
> SQL-Query with only the subset fetched from the database? If so, this
> seems worth to document though.
>
  The filter you sent as example should use the layer's filter element 
and that  should be used when retrieving the data at the postgis level. 
When the layer is in debug mode,  MapServer 5.6.x logs in this case 
shows something like (which indicates that the filter is used at the 
postgis level)
...
msPostGISLayerWhichShapes  query: select .... and ( (NAME like 'Syd%' 
escape '!') )
...

Don't you get similar logs?


>
> Best
>
> 	Stephan
>
> [1]
> http://demo.mapserver.org/cgi-bin/wfs?&VERSION=1.0.0&SERVICE=WFS&REQUEST=GetFeature&TYPENAME=cities&Filter=%3CFilter%3E%3CPropertyIsLike%20wildcard=%27*%27%20singleChar=%27.%27%20escape=%27!%27%3E%3CPropertyName%3ENAME%3C/PropertyName%3E%3CLiteral%3ESyd*%3C/Literal%3E%3C/PropertyIsLike%3E%3C/Filter%3E
>


-- 
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Assefa Yewondwossen
Software Analyst

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

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