Conditional branch algorithm in QGIS modeler link to a certain layer and certain columm

Question

I´ve got a modeler, which has limitation for the input.

I want to build a conditional branch which stops the algorithm when the limit is overstepped.

• "example" - colum with numbers from input layer
• 'Layer A' - Layer contains the maximum of "example" in colum "max_example"
• "max_example" - colum with maximum of "example"
• I use QGIS 3.16.5

With Refactor Fields --> maximum("example") I get Layer A with the colum "max_example" which contains the maximum from the input layer in the colum "max_example"

Now I want the conditional branch to check if the "max_example" ist lower than 17. The code I tried and some other variants with ' ' and " " are:

attribute(get_feature_by_id(  @Refactor_Fields_OUTPUT ,'1'),'max_example')<17

attribute(get_feature_by_id(  '@Refactor_Fields_OUTPUT' ,'1'),'max_example')<17

attribute(get_feature_by_id(  '@Refactor_Fields_OUTPUT' ,'1'),"max_example")<17

The result in the modeler is always NULL. When I try the code in the field calculator and replace '@Refactor_Fields_OUTPUT' with an actual layer it works. Looks like this so far:

 attribute(get_feature_by_id(  'Überarbeitet_a9e58d3d_4afa_494d_8be2_3c3bfcad0911' ,'1'),'max_example')

How can I link in the conditional branch to a certain layer and a certain field?

Answer 1

According to https://github.com/qgis/QGIS/issues/39119#issuecomment-768642727 this is currently not possible as those variables do not update in the scope of the model.