[Qgis-developer] Field Calculator "permanence"

[Zoltan Szecsei]

Hi Matthias,
Thanks for the quick answer.
The virtual field acts just like I want it to, except that it does not 
permanently store the column in the attribute table.
I tried getting clever by then adding a second 'Field Calculation' to 
update the existing 'Sheet' field from the virtual field, but that won't 
do it either.

So, for me there are two shortcomings:

 1. To be able to store and recall the 'Expression' and not lose it
    after closing the Field Calculator
 2. To be able to add the virtual fields that you create, into the
    attribute table.
 3. (And then of course to re-open the Shape file on another PC and have
    these Field Calculations still functional)

Any further possibilities I can try?

Regards & thanks again,
Zoltan


On 2014/11/07 18:01, Matthias Kuhn wrote:
> Hi Zoltan,
>
> Since QGIS 2.6 this possibility exists. It is called "Virtual Field".
> You must not create the attribute when creating the shapefile. Just open
> the field calculator, create a new field in there and check the "virtual
> field" checkbox.
>
> Regards,
> Matthias
>
> On 07.11.2014 16:54, Zoltan Szecsei wrote:
>> Hi,
>> I'm using QGIS 2.6.0 on Win 7 x64 - installed via OSGEO4w
>>
>> Is there a way to store your field calculator expression to always
>> process and update that specific field, should geometry be edited or
>> created for that Layer?
>>
>> Let's say I want to create a blank POINT shape file, with a text
>> attribute called "Sheet".
>> Whenever a POINT is created or moved, I want this field to be
>> dynamically updated with:
>>
>>       tostring(abs(toint($y)))+tostring(abs(toint($x)))
>>
>> For testing thus far have:
>>
>>    * created 2 points
>>    * Opened the field calculator, clicked 'Update Existing Field' and
>>      put in the expression.
>>    * The two existing points now have the correct TEXT values in the
>>      Sheet field
>>    * I close the Field calculator
>>    * Create a new point in my layer
>>    * open the attribute table to find that the 'Sheet' field for this
>>      new point is blank
>>    * I open the Field Calculator and I cannot even find a way to call
>>      back the previous expression I used.
>>
>>
>> Am I using the correct QGIS functionality to achieve what I need to,
>> and if so, where am I going wrong?
>>
>> Thanks & regards,
>> Zoltan
>>
>>
>> -- 
>>
>> ===========================================
>> Zoltan Szecsei PrGISc [PGP0031]
>> Geograph (Pty) Ltd.
>> GIS and Photogrammetric Services
>>
>> P.O. Box 7, Muizenberg 7950, South Africa.
>>
>> Mobile: +27-83-6004028
>> Fax:    +27-86-6115323     www.geograph.co.za
>> ===========================================
>>
>>
>> _______________________________________________
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>


-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028
Fax:    +27-86-6115323     www.geograph.co.za
===========================================

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