MapServer, PostGIS, Subquery with JOIN, WMS GetFeatureInfo / Followup Question

[Yewondwossen Assefa]

Hi There,

  From what I can see in the code, here is what you should do :

    * when doing the GetFeatureInfo use the request parametetr 
FEATURE_COUNT and set it to be above 1. The default is 1. This would 
trigger the nquery.
    * define on your server FEATURE_INFO_MIME_TYPE metadata to something 
like text/html
    * do your wms request with info_format=test/html (same mime type 
that the one defined in the map)

   This conditions should normally trigger all the logic used when doing 
regular query with the mapserver cgi (with the template processing).

  Give it a try and let me know. If It does not work, I can dig more 
into it.

Later,


Paul Ramsey wrote:
> Nick,
> 
> The answer to this takes either Assefa's input, or a browse of the  
> source code to find out what the GetFeatureInfo is going.  It is  
> probably doing a 'query' rather than an 'nquery', so having a multi- 
> item template may make no difference at all.  The WMS spec is silent  on 
> what the actual behavior of the GetFeatureInfo should be, so it is  very 
> much an implementation question.
> 
> Paul
> 
> On 24-Feb-06, at 12:59 PM, Nick Floersch wrote:
> 
>> I thought of a way to rephrase/reask the question I am now stuck with.
>>
>> I was reading through my MapServer book ('Beginning MapServer') on  
>> Queries and Joins, to see if mr. Kropla had any suggestions.
>>
>> He wrote that, in doing regular MapServer JOINs, if you want to  have 
>> a JOIN produce one-to-many results, you need to specify a  template 
>> for the JOIN to format each record beyond the first one  that is 
>> returned into the final HTML result. Otherwise, only the  first record 
>> will be returned.
>>
>> How does this principal apply to the GML generated by  GetFeatureInfo 
>> requests? Obviously we don't need to define a valid  HTML template to 
>> output the data... but how do GetFeatureInfo  requests deal with 
>> one-to-many situations, and does the output  format make any 
>> difference on how it is handled? If I have my  GetFeatureInfo request 
>> return HTML rather than GML, can I use  templates and have it handle a 
>> one-to-many arrangement succesfully?
>>
>> Thoughts, ideas?
>>
>> Thanks!
>> Nick Floersch
>>
>> From: Nick Floersch
>>
>> Hello Paul, Steve, Jeff, and other MapServer users,
>>
>> Thanks for the replies.
>>
>> By adding an appropriate 'using unique' clause to my DATA entry in  
>> the mapfile, I got my layer based on a view to draw. I am glad that  
>> views can be used.
>>
>>
>> There is a trick that had to be realized. At first, I put in a  'using 
>> unique the_geom' clause which of course assumed that my  geometry 
>> field was unique. But, because the source of my layer is a  view (or a 
>> subquery in its previous life) which has a left outer  join in it, the 
>> geometry column is far from unique. This is what I  thought I wanted - 
>> to generate a layer which had multiple points at  the same locations 
>> with different attributes... a series of  attributes for a given point 
>> location. In my case, the idea is that  the feature point can have 
>> images associated with it from a table  of images. So, a left outer 
>> join on that table gives me a layer  with duplicate points that have 
>> different values for the image name  attribute.
>>
>> Anyway, initially, after I realized that 'the_geom' is not a unique  
>> field for me, I switched to using a field that is unique in my  view, 
>> and things came to life. My GetFeatureInfo requests suddenly  started 
>> returning attributes, and life looked good.
>>
>> But no. Not perfect. What I had in mind has not worked quite right  - 
>> my GetFeatureInfo tool clicks on a point feature, and I get a  list of 
>> attributes, by layer, for each feature under the pointer.  Except, not 
>> all the duplicate point features are returned. The best  I can think 
>> to describe it is this: I have a stack of points all  defined in the 
>> same layer, and I click on the stack, and only the  top point in that 
>> stack is returned. I was hoping it would return  data for each of 
>> those points in the stack.
>>
>> So, is there some way I can make this work better? Am I totally  
>> barking up the wrong tree? I have one GetFeatureInfo request that  
>> needs to return multiple values for the same field of a given  
>> feature, based on a join...
>>
>>
>> Thanks for any thoughts and help!
>>
>> Nick Floersch
>>
>> -------
>>
>> If you have the option, please don't use oid, use a primary key  (like 
>> the 'gid' created by shp2pgsql) as your unique key. Primary  keys 
>> already have indexes, oids do not. Primary keys show up  automatically 
>> in a "select *" query, oids do not. oids are
>>
>> deprecated in pgsql and not available by default in pgsql 8.1.
>>
>> Basically oid is now a deadend, and we need to start erasing all  uses 
>> of them.
>>
>> P
>>
>> -------
>>
>> Nick,
>>
>> I seem to remember a post from one of the postGIS guys awile back  the 
>> you needed to add an entry in the geometry_columns table for  the view.
>>
>> -Steve W.
>>
>> --------
>>
>> This is on my "figure out some day myself" list, too. I'm doing the  
>> view thing right now, but I'd like to not have to create views for  
>> everything.
>>
>> > The only thing I can think of is... does the PostGIS connector  require
>>
>> > the table to have OIDs? It looks that way.
>>
>> Yes. It needs some unique field in order to randomly access an  
>> individual rows, it just so happens that OID is a convenient way to  
>> get that in most cases. You can also specify your own unique column  
>> name with "using unique <column name>" if your view doesn't have an  
>> OID column but you have some other key you can use. I just pull in  
>> the OID from the main geometry-containing table when I define the  view.
>>
>> -- 
>>
>> Jeff Hoffmann


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Assefa Yewondwossen
Software Analyst

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

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