Looking for assistance to set up appropriate configuration to enable drop-down lists values to be filtered based on a previous value.
Basically, I have a 3-tiered categorisation structure to one of our GIS layers - Class > Type > Sub Type.
Once Class has been selected I would like the Type list to be filtered to only values relevant for that class and so on for Sub-Type.
I have turned this into Code Value list attribute tables and loaded inot QGIS as attribute tables -
I have used these tables as Value Relation lists in the widget properties
The drop down lists work fine without a filter. But as soon as I try adding a filter with an expression, there is nothing in my drop down... If I simply type "CLASS_ID" = 1 ... I do limit the list to only those for Class = 1. The expression on it's own (attribute($currentfeature, 'LU_CLASS') correctly populates the integer values if I use it to populate a virtual field in the expression builder...
Can anyone provide any guidance as to why this doesn't work in the widget filter?
I have also (briefly) tried to set up a relation in the project properties... but this feels like I am going about it the wrong way... the records aren't a child or related to this other table - I simply want to use them to populate drop-down lists.
Am I just missing a simple step?