Mapview dynamic theme generation questions

Question

In exercising the MapViewer tool with thematics map I had a view questions on the capabilities of the component:
1. Is there a way in the map _request element reference a dynamically defined expression (column)
that is returned from the query defined in the value of the "<jdbc_query>" element. I want to show counts from an inline view,
but for brevity consider the the SQL
select geom, state , state || '-' || state_abrv concat_state_name from states
It seems that both the "label_column" attribute of the "<jdbc_query>" element and the "column" attribute of a "<rule>" element in
a style rule can only reference columns that exist in the base table either of the base map/theme or in the query .
I cannot seem to use a specification of "concat_state_name"
in the "label_column" attribute ... throws ClassCastException. Should this be possible ?
If not would the workaround would appear to use a view that is dynamically defined and insert a new map based on the view ?
2. In my inline view example, I found in the "<jdbc_query>" element that when I specifed a "render_style" that
was an advanced style with buckets it automatically selected my count expression and rendered the map correctly, which
is great, but it might be a good idea to make it explicit if 1. could be handled (or can).
3. For thematic maps it would be nice to dynamically define the buckets (<AdvancedStyle>)
within the map request as the potient for permutations of numeric ranges in any application could vary.
It looks like <styling_rules> might be able to handle this if you can use the BETWEEN operator or something
like runway_number >= 10 and runway_number < 20 as expressions. Are these valid and if so where are they specified
in the map_request ? I did not see them nested anywhere in the DTD yet the Example 2-1 in the documentation would
imply they can be specified in the map request and the tool map definition tool does not seem to support the concept of a
variable in the base table. The workaround would appear to be to dynamically add the theme using an insert.

Answer 1

In exercising the MapViewer tool with thematics map I had a view questions on the capabilities of the component:
1. Is there a way in the map _request element reference a dynamically defined expression (column)
that is returned from the query defined in the value of the "<jdbc_query>" element. I want to show counts from an inline view,
but for brevity consider the the SQL
select geom, state , state || '-' || state_abrv concat_state_name from states
It seems that both the "label_column" attribute of the "<jdbc_query>" element and the "column" attribute of a "<rule>" element in
a style rule can only reference columns that exist in the base table either of the base map/theme or in the query .
I cannot seem to use a specification of "concat_state_name"
in the "label_column" attribute ... throws ClassCastException. Should this be possible ?
If not would the workaround would appear to use a view that is dynamically defined and insert a new map based on the view ? MapViewer does allow dynamic expressions in <jdbc_query>. Can you test the following simple request:
<?xml version="1.0" standalone="yes"?>
<map_request datasource = "mvdemo">
<themes>
<theme name="theme1" min_scale="5.0E7" max_scale="0.0">
<jdbc_query
datasource="mvdemo"
jdbc_srid="0"
spatial_column="geom"
render_style="C.RED"
label_style="T.STREET NAME"
label_column="concat_state_name"
>select geom, state , state || '-' || state_abrv concat_state_name from states where state_abrv='MA' </jdbc_query>
</theme>
</themes>
</map_request>
As long as the name specified in lable_column matches the alias you give in the select list it should work.
If not then maybe you need to use the view-based approach. It will definately work in the up-coming 9.0.4 version.
2. In my inline view example, I found in the "<jdbc_query>" element that when I specifed a "render_style" that
was an advanced style with buckets it automatically selected my count expression and rendered the map correctly, which
is great, but it might be a good idea to make it explicit if 1. could be handled (or can).
3. For thematic maps it would be nice to dynamically define the buckets (<AdvancedStyle>)
within the map request as the potient for permutations of numeric ranges in any application could vary.
It looks like <styling_rules> might be able to handle this if you can use the BETWEEN operator or something
like runway_number >= 10 and runway_number < 20 as expressions. Are these valid and if so where are they specified
in the map_request ? Yes that may indeed be a good thing to have in a future version of mapviewer. In the mean time yes you can always use such expressions as you provided in the styling_rules (which is only for predefined themes) or in a <jdbc_theme>.
I did not see them nested anywhere in the DTD yet the Example 2-1 in the documentation would
imply they can be specified in the map request and the tool map definition tool does not seem to support the concept of a
variable in the base table. The workaround would appear to be to dynamically add the theme using an insert. The map definition tool is lagging behind in terms of supporting all the functions actually available in MapViewer server.
Thanks,
LJ