In Value Relation widget the new function current_value in filter expression is not affected by a settext of a python initialization function.

[qgib]

Author Name: Alain FERRATON (@FERRATON)
Original Redmine Issue: 21852
Affected QGIS version: 3.4.5
Redmine category:forms

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I'm not sure it's a bug, because the problem is a bit complex.

I am in a case where I have to initialize a field, in reality by recovering a value in another layer that contains the entered point, but for the example just by assignment in a form open function

from PyQt5.QtWidgets import QDialogButtonBox, QLineEdit
def my_form_open(dialog, layer, feature):
dialog.findChild(QLineEdit,'id').setText('10')

Another field (ref) is defined as a relational value and uses a filter for this purpose
id" = current_value("id')

when the form is initialized, the id value is not recovered by the current_value() function. All layer values are displayed instead of being filtered.
it is necessary to retype the value in the field so that the field 'ref' is filtered

In the same case, the formValuerelation plugin worked correctly with QGIS 2.

attached two layers gpkg and a project for testing

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• test.qgz (Alain FERRATON)
• MyLayerA.gpkg (Alain FERRATON)
• ref.gpkg (Alain FERRATON)

[FERRATON]

dataset.zip
the file ref.gpkg in the data set was empty.

[FERRATON]

Another problem that may be related.
If you enter the filter field manually, the combobox is updated.
but if , for example, you choose the 2nd value in the list, it is displayed, but when you save, the 1st value is saved.

example if you enter 10 the list will be for example 10a, 10b, 10c... we choose 10b which is displayed, but it is the value 10a which is saved.

[troopa81]

I'm not sure this really an issue. When forcing the value at form opening the relational widget (the combobox) is filtered as expected. The value ref is indeed not modified but it looks normal to me to not change the value, it's the user choice to change or not the value.

We get the same behavior when changing the value id manually, the ref value isn't changed until you decide to edit the value through the relational widget.

I fail to reproduce the second issue, the expression id_ref = current_value('id') didn't give a list with 2 elements because "10" != "102", but even with this expression left(id_ref,2) = left(current_value('id'),2) everything works fine.

[troopa81]

Proposed PR #30554