expression like "CASE WHEN "other_column" = 'no' THEN NULL END" work on QGIS, block/lock column on MM

[gioman]

Description

In a form in QGIS set the default value for a column as

CASE WHEN "other_column" = 'no' THEN NULL END

This works perfectly fine, if "other_column" value is set to "no" (in my case with a checkbox widget) then the content of the column where the default is applied is set/reset to NULL.

On the other hand on MM App this expression has the effect of blocking/locking the column, meaning that it turn as if was set to be not editable.

MM plugin 2026.3.0
MM App 2026.2.0

[Withalion]

Hello @gioman, thanks for reporting this issue, we will look into it.

[tomasMizera]

Hi @gioman, I guess your field is configured with "apply default value on update", right? In this case we intentionally force such form widgets to be read-only. Happy to hear more about your use case though.

[gioman]

Happy to hear more about your use case though.

@tomasMizera Hi Tomas, thanks for the reply. Our use case is the following, you can easily look at it in a more general case.

Work is surveying trees.
User needs to tell which specie it is ("nome comum"), for example with a list

On second thoughts the user realize that is unsure about it and maybe is a specie that is not on the list, so it check the "no classification" ("sem classificação") checkbox to show a field (previously hidden) to manually enter a specie or a note

Doing this is highly expected for "nome comum" to be cleared (and vice versa too) and the described expression does that, but it only works on Desktop.

[tomasMizera]

Hi @gioman, so the problem is that your column "Melhor identificacao" is read-only in the mobile app, correct?

[gioman]

Hi @gioman, so the problem is that your column "Melhor identificacao" is read-only in the mobile app, correct?

@tomasMizera in the specific case no, the field that becomes read only is the one with the list ("nome comum"). The idea is that when something was selected from the list, then if another field change value (in this case "sem identificacao") then the field with the list is reset to NULL. But this do not only apply to this case with a list and a checkbox, is true also for other widgets as simply as "text" fields. Tested again on Desktop just to be sure and it works as expected.

[tomasMizera]

Hi @gioman, I sent you an email to discuss this further as it tightly relates to your specific project :)

[gioman]

@tomasMizera I booked a slot, happy to speak about it even tough I don't think is a very special case, maybe not super common, but a general one anyway.