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Hi,<br>
<br>
What you probably ask for are database triggers combined with
storage. This is not what virtual fields are for. If they were
stored - they wouldn't be called virtual ;-)<br>
<br>
You can do that f.e. with Postgis. With shapefiles not. However, if
you share the project with the other PC, the virtual fields work
fine.<br>
<br>
Andreas<br>
<br>
<div class="moz-cite-prefix">On 07.11.2014 17:21, Zoltan Szecsei
wrote:<br>
</div>
<blockquote cite="mid:545CF16F.20604@geograph.co.za" type="cite">
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<div class="moz-cite-prefix">Hi Matthias,<br>
Thanks for the quick answer.<br>
The virtual field acts just like I want it to, except that it
does not permanently store the column in the attribute table.<br>
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.<br>
<br>
So, for me there are two shortcomings:<br>
<ol>
<li>To be able to store and recall the 'Expression' and not
lose it after closing the Field Calculator</li>
<li>To be able to add the virtual fields that you create, into
the attribute table.</li>
<li>(And then of course to re-open the Shape file on another
PC and have these Field Calculations still functional)<br>
</li>
</ol>
Any further possibilities I can try?<br>
<br>
Regards & thanks again,<br>
Zoltan<br>
<br>
<br>
On 2014/11/07 18:01, Matthias Kuhn wrote:<br>
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<blockquote cite="mid:545CECD7.9030808@gmx.ch" type="cite">
<pre wrap="">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:
</pre>
<blockquote type="cite">
<pre wrap="">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 <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
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<br>
<br>
<pre class="moz-signature" cols="72">--
===========================================
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 <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
===========================================</pre>
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