[Qgis-developer] Virtual columns in QGIS, was: Re: [Qgis-user] object labels

[Andreas Neumann]

 Hi Nathan,

 Good to hear that you are working on this.

 I just wonder if it wouldn't make sense to have a general purpose 
 "virtual column" that could be introduced in QGIS. This would be useful 
 for:

 * labeling
 * map tips/QGIS server tooltip display
 * symbology
 * plugins
 * others?

 It would be convenient to use the field calculator, but instead of just 
 writing out to a physically existing column it would create a new 
 virtual column, just like a virtual column in a database view.

 Otherwise one would have to develop the same functionality several 
 times - for labeling, for tooltips, etc.

 Do you think it would be feasible to implement this on a lower level in 
 QGIS so that users could transparently work with virtual columns 
 wherever they want?

 Andreas

 On Thu, 28 Jul 2011 16:09:56 +1000, Nathan Woodrow wrote:
> My upcoming patch that adds expression based labels will be able
> to achieve this once it's completed;  I'm just cleaning up the UI
> and testing everything then I will get the guys to merge it in.
>  Until then you will need to create a new column.
>
> - Nathan
>
> On Wed, Jul 27, 2011 at 9:15 PM, Torsten Lange  wrote:
>
>> Ok, thank you, Andreas!
>>
>> Torsten
>>
>> Am Mittwoch 27 Juli 2011, 11:00:01 schrieb Andreas Neumann:
>>
>>>  Hi,
>> >
>> >  Currently, you have to create a new column. I usually create a
>> view in
>> >  Postgis for this purpose.
>> >
>> >  It is in on the wishlist that one can create a "virtual" column
>> - not
>> >  only for labeling, but also for map tips and perhaps
>> symbolization.
>> >  Until then you have to do it yourself.
>> >
>> >  Andreas
>> >
>> >  On Tue, 26 Jul 2011 22:51:34 +0200, Torsten Lange wrote:
>> > > Hi,
>> > >
>> > > Is there a way just to print - lets say - the first four
>> letters of a
>> > > objects
>> > > name? Or must I create a new row for that?
>> > >
>> > > Thank you, Torsten
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>>
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 Andreas Neumann
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