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
