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

[Nathan Woodrow]

Yeah those are possible. Not 100% sure with point 2 but the others can be
done.  QGIS uses || for concatenation too.

On Thu, Jul 28, 2011 at 7:45 PM, kimaidou <kimaidou at gmail.com> wrote:

> Hi
>
> Since I have not tested your patch yet, it is hard to comment. The
> functionnalities I am thinking of for labelling purpose are :
> * be able to add uppercase to the first letters of words
> * add a line break after the first space after X letters (such as Mapserver
> does with WRAP and MAXLENGTH ( http://mapserver.org/mapfile/label.html )
> * Concatenate one or more columns with expresssions, such as : colA || '('
> || colB || ')'   (here I am using the postgresql || syntaxe )
>
> kimaidou
>
>
>
> 2011/7/28 Nathan Woodrow <madmanwoo at gmail.com>
>
>> +1 from me too.  A virtual column would be a very handy feature however
>> you must be able to add one to read only datasets eg MI Tab otherwise their
>> is no real advantage.  The expression labelling I'm working on works with
>> read only datasets.   I think the expression based labelling and the virtual
>> column thing could exist together quite well the former being a short cut in
>> the labeling gui for the latter.
>>
>> Check out http://hub.qgis.org/issues/3488 and
>> https://github.com/NathanW2/Quantum-GIS/tree/expression-labels for the
>> status of my patch.  I have been away for a couple of weeks but I will be
>> getting back into over the next couple of weeks.
>>
>> Anyone else got any other thoughts?
>>
>> - Nathan
>>
>> On Thu, Jul 28, 2011 at 6:49 PM, kimaidou <kimaidou at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> +1 for Mayeul Nathan. This "virtual column" would be a very handy tool !
>>> E.G for labelling
>>>
>>> kimaidou
>>>
>>>
>>> 2011/7/28 Andreas Neumann <a.neumann at carto.net>
>>>
>>>> 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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>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Links:
>>>>> ------
>>>>> [1] mailto:Qgis-user at lists.osgeo.**org <Qgis-user at lists.osgeo.org>
>>>>> [2] http://lists.osgeo.org/**mailman/listinfo/qgis-user<http://lists.osgeo.org/mailman/listinfo/qgis-user>
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>>>>> [5] mailto:tlange at gwdg.de
>>>>>
>>>>
>>>> --
>>>> --
>>>> Andreas Neumann
>>>> Böschacherstrasse 10A
>>>> 8624 Grüt (Gossau ZH)
>>>> Switzerland
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