[Qgis-developer] Expression based labeling

[Andreas Neumann]

 Hi,

>>> Question 1: the output preview of the label does not seem to work
> when I use a field - is there something I need to >>do to enable it? 
> I
> would expect it to pull in the first record or some random record to
> retrieve values?
>
> Ah yes there seems to be a bug with grabbing the first record with
> some data sources.  I get the top feature using layer.featureAt(0)
> but for some reason not all providers return a record at this index.
>  Writing a patch now.

 My data source is Postgis in this case.

>>>Question 2: how does it handle empty fields (null values)? would
> string concatenation still work or do we need to >>coalesce() like in
> PostreSQL?
>
> Yeah null values when used with || are just converted to empty
> strings.

 good

>>> Remark:
>>> wouldn't it be cleverer to use your great new query builder and
> introduce the concept of a "virtual column" in the >>data provider? 
>
> That would be a cool idea and something I have thought about, just
> don't have the skills or time at present.  I plan to redo the field
> calculator to use my new expression builder widget at some stage so 
> we
> can look at the virtual column thing then.

 well this was more a general question to all of the developers - not 
 that I ask that from you personally.

 Thanks again - it is really cool!

 Andreas


 --
 Andreas Neumann
 Böschacherstrasse 10A
 8624 Grüt (Gossau ZH)
 Switzerland