Unique values allow null value checkbox by MoritzMoreira · Pull Request #62750 · qgis/QGIS

MoritzMoreira · 2025-08-01T12:15:55Z

I first created the PR Value map allow null value checkbox which fixes this issue. As the modified version of the virtual QgsEditorWidgetWrapper::updateValues() can be applied to all widgets with ComboBoxes, I decided to implement my modification as a non-virtual function beside the virtual one, to avoid identical overrides for all 6 widgets with comboboxes.
I decided to create one PR for each widget type, to avoid one very large PR.

There are two motivations for making the change for the other 5 combobox widgets besides value map (unique values,, enumaration, relation reference, classification and value relation) now:

alignment of functionality.
continuation of PR Disable comboboxes with no and one item :
in the case of only one available value, this value has to be selected by default, because the combobox will be disabled

The null value is represented this way in the combobox, rather then with no representation as of now. Also, one of the available values is set as default on opening the widget editor, rather then setting the comboBox to index -1 (no selection).

The adaptation of the default value preview is done in this PR.

github-actions · 2025-08-01T13:38:27Z

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m-kuhn

Thanks for this pull request.
There are a few things to reconsider regarding where methods live, QgsFieldFormatter and QgsEditorWidgetWrapper are generic base classes, so they should not contain unique values widget specific code.

signedav · 2025-08-11T13:36:10Z

+    if ( comboBox->findData( v ) == -1 )
+    {
+      // v != "" is to check for the autogenerated null value, which should be represented as "()" instead of "(Null)".
+      if ( allowNull && !v.isEmpty() )


I don't get that. On line 157 you set v to the NULL_VALUE in case it's null. Otherwise it's a string. Why is this check here needed?

I think you are right, I cannot reproduce the situation where this autogenerated value is passed anymore. I have simplified the function accordingly and I think I have tested all cases (0/1 entry in value map table, allow null (un)checked, (un)valid default value, and all their combinations).

What about backwards compatibility btw.? Is it concerned when the allowNull setting is not set (because configured with older QGIS) but NULL values are in the list?

As it is, the NULL values from the table are added to the combobox, even when allow NULL is unchecked. Should the user get a message about it, and/or the addition of the null values be blocked? I think the rows should not be deleted automatically, because the user might want to go back to the old QGIS, correct?

@m-kuhn What do you think about that? (the backwards compatibility part)

@MoritzMoreira Could you implement the backwards compatibility here? Means that you are able to load old projects: e.g on widget init set allow null if you have a null value (and remove the null value) and same in the widget configuration (but then stored again the new way). So you are able to use older project on newer QGIS versions (not being able to use new projects on old QGIS versions is fine I guess).

FYI: I hope I will get to do this soon, but I am not sure when I'll have the time. I will continue this whole project and some point.

I have added the backwards compatibility.

signedav · 2025-08-12T10:34:54Z

+    // check if the value was already added to the combobox
+    if ( comboBox->findData( v ) == -1 )
+    {
+      // only if "allow null" is checked a null value is added


Won't this add NULL multiple times?

I could not produce the situation, I think it is because the function only get's called once. Should I add
&& comboBox->findData( QgsFieldFormatter::NULL_VALUE ) == -1 )
just in case, before adding NULL?

Maybe this would be necessary in the case of a set default value and the call of QgsEditorWidgetWrapper::setValues()? I could not work out how to do the latter in the python console and have it reflected in the added layer in the GUI yet.

Not 100% sure, but I thinks that it should check if QgsFieldFormatter::NULL_VALUE is already in the list.

It's in my opinion a little bit confusing structured. See below.

signedav · 2025-08-12T11:26:55Z

+  QString v = value.toString();
+
+  if ( comboBox )
+  {
+    // check if the value was already added to the combobox
+    if ( comboBox->findData( v ) == -1 )
+    {
+      // only if "allow null" is checked a null value is added
+      if ( config( QStringLiteral( "AllowNull" ) ).toBool() )
+        comboBox->addItem( QgsApplication::nullRepresentation().prepend( '(' ).append( ')' ), QgsFieldFormatter::NULL_VALUE );
+      // add the value
+      if ( !QgsVariantUtils::isNull( value ) )
+        comboBox->addItem( v.prepend( '(' ).append( ')' ), v );
+    }


I think I would rather structure it like this (just draft - and untested)

if ( comboBox ) { if ( !QgsVariantUtils::isNull( value ) ) { QString v = value.toString(); if ( comboBox->findData( v ) == -1 ) { comboBox->addItem( v.prepend( '(' ).append( ')' ), v ); } } else if ( config( QStringLiteral( "AllowNull" ) ).toBool() && comboBox->findData( QgsFieldFormatter::NULL_VALUE) == -1 ) { comboBox->addItem( QgsApplication::nullRepresentation().prepend( '(' ).append( ')' ), QgsFieldFormatter::NULL_VALUE ); } }

What do you think?

yes, that is better. I have tested commited the changes.

github-actions · 2026-01-13T03:06:28Z

The QGIS project highly values your contribution and would love to see this work merged! Unfortunately this PR has not had any activity in the last 14 days and is being automatically marked as "stale". If you think this pull request should be merged, please check

that all unit tests are passing
that all comments by reviewers have been addressed
that there is enough information for reviewers, in particular
- link to any issues which this pull request fixes
- add a description of workflows which this pull request fixes
- add screenshots if applicable
that you have written unit tests where possible
In case you should have any uncertainty, please leave a comment and we will be happy to help you proceed with this pull request.
If there is no further activity on this pull request, it will be closed in a week.

github-actions · 2026-01-20T03:10:20Z

While we hate to see this happen, this PR has been automatically closed because it has not had any activity in the last 21 days. If this pull request should be reconsidered, please follow the guidelines in the previous comment and reopen this pull request. Or, if you have any further questions, just ask! We love to help, and if there's anything the QGIS project can do to help push this PR forward please let us know how we can assist.

github-actions · 2026-10-02T02:46:52Z

The QGIS project highly values your contribution and would love to see this work merged! Unfortunately this PR has not had any activity in the last 14 days and is being automatically marked as "stale". If you think this pull request should be merged, please check

that all unit tests are passing
that all comments by reviewers have been addressed
that there is enough information for reviewers, in particular
- link to any issues which this pull request fixes
- add a description of workflows which this pull request fixes
- add screenshots if applicable
that you have written unit tests where possible
In case you should have any uncertainty, please leave a comment and we will be happy to help you proceed with this pull request.
If there is no further activity on this pull request, it will be closed in a week.

Non-virtual version of updateValues() specific for all the widgets with a combobox and allow-null-value configuration parameter.

Addition of a "Add NULL value" checkbox, enabling the addition of a NULL value to the combobox when there are no features.

- the widget's combobox offers a null value for layers from older versions when there is a null value in the field - when opening the configuration widget for the first time, the allow null checkbox is set accordingly - Null values are no longer added to the combobox in qgsuniquevaluewidgetwrapper:initWidget()

As of now the unit test contains only tests for the unique values widget. Tests for the other widget types will be added in the respective PRs.

MoritzMoreira · 2026-10-29T16:41:24Z

Is there anything I can do about the failed WASM check ?

elpaso · 2026-10-29T18:08:47Z

Is there anything I can do about the failed WASM check ?

Just ignore it.

github-actions Bot added this to the 4.0.0 milestone Aug 1, 2025

MoritzMoreira marked this pull request as draft August 1, 2025 12:18

MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from 67d1047 to 0b1a434 Compare August 1, 2025 12:37

MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from 0b1a434 to cf08eda Compare August 1, 2025 17:00

m-kuhn reviewed Aug 4, 2025

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch 3 times, most recently from da8c72e to 0b0d78f Compare August 5, 2025 17:37

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch 3 times, most recently from 15ed34e to 7a131eb Compare August 6, 2025 16:38

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from 7a131eb to 31c3f3a Compare August 7, 2025 12:07

MoritzMoreira mentioned this pull request Aug 7, 2025

Classification allow null value checkbox #62802

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from 31c3f3a to 05ec425 Compare August 8, 2025 08:24

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from cd17a17 to 26cb2f4 Compare August 12, 2025 10:23

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github-actions Bot added stale Uh oh! Seems this work is abandoned, and the PR is about to close. and removed stale Uh oh! Seems this work is abandoned, and the PR is about to close. labels Dec 27, 2025

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github-actions Bot added stale Uh oh! Seems this work is abandoned, and the PR is about to close. GUI/UX Related to QGIS application GUI or User Experience Form and removed stale Uh oh! Seems this work is abandoned, and the PR is about to close. labels Sep 12, 2026

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MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch 2 times, most recently from 5bec983 to c191eb3 Compare October 16, 2026 14:18

MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch 4 times, most recently from 34bcd05 to b04091f Compare October 28, 2026 13:49

MoritzMoreira added 4 commits October 28, 2026 16:35

new implementation of the function updateValues

ffe6b60

Non-virtual version of updateValues() specific for all the widgets with a combobox and allow-null-value configuration parameter.

Allow null value checkbox

90e09d2

Addition of a "Add NULL value" checkbox, enabling the addition of a NULL value to the combobox when there are no features.

unit test

320dcf2

As of now the unit test contains only tests for the unique values widget. Tests for the other widget types will be added in the respective PRs.

MoritzMoreira force-pushed the unique-values-allow-null-value-checkbox branch from b04091f to 320dcf2 Compare October 28, 2026 16:38

MoritzMoreira marked this pull request as ready for review October 28, 2026 18:26

Merge branch 'master' into unique-values-allow-null-value-checkbox

e0e83c8

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