[mapguide-users] How to use Select Aggregates in MapGuide

[Kenneth Skovhede, GEOGRAF A/S]

To answer my own question:

The computed properties and the alias must be used together.
This is similar to addComputedPropertie(alias, expression).
Multiple aliases and multiple expressions must be seperated with TABS 
(pretty difficult to do in a browser).

To use the SpatialExtent function, simply enter a name in the Alias 
field, eg: extent,
then enter SpatialExtents("name of geometry column") in the computed 
properties field.

Aggregates does not work with geometry columns, but does work with the 
SpatialExtents function.

And the OGR provider, which I used, does not support the aggreate 
instructions, and seems to ignore
any computed properties :(.

Regards, Kenneth Skovhede, GEOGRAF A/S



Kenneth Skovhede, GEOGRAF A/S skrev:
> I'm having trouble understanding how the "Select Aggregates" system 
> works.
> I expect it to be similar to the "GROUP BY" SQL command.
>
> But, on the test page:
> http://localhost/mapguide/mapagent/selectfeaturesform.html
>
> I have the fields "Properties" and "Computed Properties".
> If I enter nothing in the "Properties" field, or the name of a spatial 
> column, I get a "Type error".
> If I enter the name of an existing column, I get all the rows 
> containing this column.
>
> The "Computed Properties" field seems to accept anything, and has no 
> effect on the output.
>
> I would like to calculate the actual extents of the geometry of the 
> entire featuresource.
> There seems to exist an FDO command called "SpatialExtents", but I 
> don't see how I
> can use that function from MapGuide.
>
> Any help is appreciated!
>