[QGIS-Developer] Question on current_value() expression in the context of filtering relation reference combo boxes

[Andreas Neumann]

Hi Ale,

Thanks for your information.

What if both tables have the same column names? Would that also work?

In my case the related table contains a field called "szenario_art" and 
the parent table also has the same field name.

Can one assume that a field left of the operator will be in the related 
table while fields right of the operator are in the parent table? Or how 
would the expression distinguish the fields if they appear in both 
tables?

Thanks,
Andreas

On 2022-12-06 16:29, Alessandro Pasotti wrote:

> On Tue, Dec 6, 2022 at 3:59 PM Andreas Neumann via QGIS-Developer
> <qgis-developer at lists.osgeo.org> wrote:
> 
>> Hi,
>> 
>> In one of my form setups,  I would like to filter one relation 
>> reference widget combo box with a filter expression based on the 
>> selected entry of another relation reference value.
>> 
>> A static filter like:
>> 
>> szenario_art = 'Brand'
>> 
>> works as expected and it returns the filtered values - but as soon as 
>> I try to base it on the value of another relation reference widget, it 
>> fails ...
>> 
>> I tried
>> 
>> szenario_art = current_value('szenario_art')
>> 
>> but no records get selected.
>> 
>> Questions:
>> 
>> Does the current_value() return the "internal value" or the "human 
>> readable" value?
> 
> The internal value.
> 
>> Do I have to eval() something in the filter expression?
> 
> No.
> 
>> Is there a way to test "current_value" somehow? I tried to write the 
>> changed value into another text widget (with default values on 
>> update), but it will always return "NULL". In the expression editor, I 
>> also always get "NULL" in the preview.
> 
> That should work, the current_value returns the current value of the
> feature being edited in the context of the form, this includes any
> change that took place in the form.
> 
> You might get null values in the editor and the preview because there
> is no form context in that case.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20221206/613c49df/attachment.htm>