MapServer 7 arithmetic expressions do not work on STYLE attributes

Question

I am trying to port my code from MapServer 5 (Oracle) to MapServer 7 (PostgreSQL), but I am encountering a issue when trying to apply arithmetic expressions in the style class. So previously in MapServer 5 I would have something like:

DATA "geom from (select pk, geom, size from sizes_of_thing) USING srid 3788 version 11g"
CLASS
    MAXSCALEDENOM 5001
    STYLE
        COLOR [size*2]

Which worked perfectly fine: But if I convert it to MapServer 7 and PostgreSQL like:

DATA "geom from (select pk, geom, size from sizes_of_thing sot) USING unique pk USING srid=3788"
CLASS
    STYLE
        COLOR [size*2]

Throws an error such as:

msPostGISLayerWhichShapes(): Error (ERROR:  column "size*2" does not exist

By any chance are these expressions not supported anymore in MapServer 7/PostGIS or am I doing something wrong?

What I have tried so far is to write something like

SIZE [size]*2
SIZE ([size]*2)

create an expression like:

EXPRESSION ("size2" "[size]*2")

And use it in something like:

SIZE [size2]

create a validation variable such as:

VALIDATION
"size2" '[size]*2'

and then

SIZE [size2]

But seems like none of them work.

Answer 1

It is documented https://www.mapserver.org/mapfile/style.html that mathematical expressions are not supported for angle:

If you have an attribute that specifies angles in a clockwise direction (compass direction), you have to adjust the angle attribute values before they reach MapServer (360-ANGLE), as it is not possible to use a mathematical expression for ANGLE.

Maybe the same applies to other style items as well.

In that document page the only place where expression is mentioned is in GEOMTRANSFORM [bbox|centroid|end|labelcenter|labelpnt|labelpoly|start|vertices|<expression>]

Also in https://www.mapserver.org/mapfile/expressions.html

As of version 6.0, expressions are used in four places:

• In LAYER FILTER to specify the features of the dataset that are to be included in the layer.

• In CLASS EXPRESSION to specify to which features of the dataset the CLASS applies to.

• In CLASS TEXT to specify text for labeling features.

• In STYLE GEOMTRANSFORM.

It seems that current MapServer version does not support your use case for expressions. You may write mail to mapserver-users mailing list and ask for confirmation.