QGIS Modeller- Field Calculator on intermediate step fails to find field

Question

As part of my model I union a bunch of PostGIS layers (views), each containing the same 'feature' field (char(64)). After the union, there are a numerous feature_2, feature_3 etc etc fields in the output. Example View: Model I want to store these values into the original 'feature' field but the field calculator does not recognise the fields?

Field Calculator- Pre Calculated Value

CASE
WHEN "feature_2" IS NOT NULL THEN '1'
WHEN "feature_3" IS NOT NULL THEN '2'
WHEN "feature_4" IS NOT NULL THEN '3'
WHEN "feature_5" IS NOT NULL THEN '4'
WHEN "feature_6" IS NOT NULL THEN '5'
WHEN "feature_7" IS NOT NULL THEN '6'
END

Result

feature setback calc: Field 'feature_2' not found Example output of the union:

Creating a temporary output from the model from the same step that the field calculator uses shows that these fields DO exist? What's going on here?

Answer 1

I found the solution to this problem was not to use a CASE but to use a COALESCE into the final field (planting_class) which will use the temporary field names (planting_class_1 2 3 etc):

coalesce("planting_class_2",
"planting_class_3",
"planting_class_4",
"planting_class_5",
"planting_class_6",
"planting_class_7",
"planting_class_8",
"planting_class_9", 
"planting_class")