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

[Nathan Woodrow]

+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:
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>>> [5] mailto:tlange at gwdg.de
>>>
>>
>> --
>> --
>> Andreas Neumann
>> Böschacherstrasse 10A
>> 8624 Grüt (Gossau ZH)
>> Switzerland
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