Question on queryByAttributes - multiple fields

[Cord Thomas]

Sean,

Thank you.  If you'd like participation in the howTo, let me know.  I
would like to contribute non-trivial examples as i put them together.

Given your discovery - i feel there may be a bug in implementation then.
I am unsure why my query results in getNumResults() = 0 though when
executed directly against the database, it returns 1 record.

Cord

> My responses inline ...
>
> On Nov 29, 2004, at 6:15 PM, Cord Thomas wrote:
>
>> Hey Sean
>>
>> Thank you for this definitive answer.  I have a few observations:
>>
>> 1 - as i said, if i see the query dump from mapserver when i forgot to
>> give my account select permissions, i saw the following statement:
>>
>> DECLARE mycursor BINARY CURSOR FOR SELECT
>> stateid,name::
>> text,asbinary(force_collection(force_2d(wkb_geometry)),'NDR'),OID::
>> text
>> from incorpbound WHERE (stateid='ME' and name='Camden') and
>> (wkb_geometry
>> && setSRID( 'BOX3D(-125 23,-66
>> 50.5)'::BOX3D,find_srid('','incorpbound','wkb_geometry') ))
>>
>> this would imply mapserver is correctly parsing my query - AND - if i
>> try
>> to execute this query against postgresql, it does return results - i
>> get
>> all excited by this.
>>
>> 2 - since query parsing is not left to mapserver (we have to provide
>> the
>> exact syntax) - there is no reason MS couldnt handle multiple field
>> criteria.
>>
>
> I looked again at the code underneath mapserver queries.  Here's what
> goes on under the hood: the queried layer has its 'filteritem'
> temporarily
> set to the 'qitem' from the query method, and its 'filter' temporarily
> set to the 'qstring'.  Then the features are filtered and indexes to the
> features become the query result set.
>
> So yes, you can do a multi-attribute query.  For a RDBMS data source,
> your qstring can be almost any SQL where clause, and for shapefile or
> OGR sources you can do complicated mapserver expressions like
>
>     qstring = "([att1] > 0 and [att2] > 0)"
>
> I guess my querying HOWTO needs major revision already :)
>
>> 3 - i see no performance issues or other technical hurdles that would
>> prevent the execution by MS of this request - unless actually it is
>> tied
>> to how this information gets back into the TEMPLATE object or is used
>> by
>> LABELs - both issues i am unclear on (like why a TEMPLATE is
>> /required/ by
>> MS for queries)
>>
>
> The template is an artifact from the CGI mode, since that's how the
> results are delivered.  I'm constantly debating with other developers
> over eliminating this artifact from mapscript.
>
>> 4 - I understood the MS_SINGLE vs MULTIPLE - though i still need to
>> learn
>> how best to work with this (one problem i have is that a city's
>> boundaries
>> may come in more than 1 record - but i really just want 1 result -
>> something i have to tinker with on my end) - thanks for the
>> explanation.
>>
>>
>> I look forward to reading more on documentation and if i can help,
>> please
>> let me know.  I am working on a prototype public participation web
>> application and i need a feature like this to work, and work quickly
>> (application performance, not how quickly i need 4.4 released).  The
>> two
>> fields are indexed and i really can't imagine that saving a query and
>> reloading it is going to be efficient, but i look forward to possibly
>> hearing from Adam.  As an alternative, i could query on the most
>> restrictive field and then iterate over the results until i find the
>> value
>> of the less restrictive field - though ugly, i guess that is an
>> alternative.
>>
>
> Since your data is in PostgreSQL/PostGIS, you can always go directly
> to the database when you need.
>
> cheers,
> Sean
>