To the list -
Please disregard my first post about this issue. I made an error by
simplifying my example. The scenario is as follows:
I have *2* columns in a table - both with a "Value Relation" setup. The
second column has furthermore a filter (/current_value('first_column') =
"some_column_in_the_lookup_table"/ ) which decides the values in the
value list for the second column based on the chosen value in the first
column - a "drill-down" effect.
In QGIS ver. 3.38 and prior versions - you could change the behavior of
the drop-down value list for the second column by checking/unchecking
the "Allow NULL value" checkbox:
* If "Allow NULL value" was checked, the chosen value in the second
column would be "blank"/not chosen.
* If "Allow NULL value" was /not /checked, the chosen value in the
second would automatically be set to the first value in the filtered
value list.
So you - as a QGIS project designer - could decide if the second column
automatically got a value from the drop-down list for the second column
when the user chose a value for the first column.
/However,/ in QGIS version 3.40 and onward, this behavior has changed.
Regardless of the state of the "Allow NULL value" checkbox, the initial
value of the widget for the second column is always "blank"/not chosen
(If manually activated, the drop down list for the second column
contains the values derived from the filter expression. So the filter
function is working)
Is this the new expected behavior or is it a regression bug ? And if it
is the expected behavior: Can you somehow enable the old behavior ??
I have many (many, many...) QGIS projects depending on the old behavior.
Use case example: I have 2 columns in a table. The first column contains
the Danish name for a tree species. The second column contains the Latin
name for the tree species. So the value in the second column is 100%
dependent on the user-chosen value in the first column. The user should
not be bothered with selecting the Latin name in the second column from
a value list with a single item.
Med venlig hilsen / Best regards
Bo Victor Thomsen
On 3/29/2025 10:47 AM, Bo Victor Thomsen wrote:
Hi list -
In QGIS ver. 3.38 and prior versions - using a "Value Relation" widget
in a attribute form - you could change the behavior of the drop-down
value list in the widget by checking/unchecking the "Allow NULL value"
checkbox:
* If "Allow NULL value" was checked, the chosen value would be
"blank"/not chosen.
* If "Allow NULL value" was /not /checked, the chosen value would be
set to the first value in the value list.
So you could decide if the field automatically got a value from the
drop-down list without any manual user action.
/However,/ in QGIS version 3.40 and onward, this behavior has changed.
Regardless of the state of the "Allow NULL value" checkbox the initial
value of the widget is always "blank"/not chosen.
Is this the new expected behavior or is it a regression bug ? And if
it is the expected behavior: Can you somehow enable the old behavior ??
I have many (many, many...) QGIS projects depending on the old behavior.
--
Med venlig hilsen / Best regards
Bo Victor Thomsen
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