Issues with Field Calculator and attribute joins in ModelBuilder

[geguill]

Hello,

• How do I express the calculation of polygon feature areas in the Field Calculator? I’ve tried $area("hectares"), ST_area(geom)...

• When I try to perform an attribute join within a model, I am unable to select the join fields (even though the process works fine in the Whitebox)!
  Thanks,
  Géguil

[giswqs]

Use this:

[geguill]

Thanks for your reply.
Creating a field to calculate area using the $area function works fine EXCEPT within a model; I get an error message: "expression evaluation failed: Function identifier is not bound to anything by context: '$area'".
(see screenshot)

I am restating my second issue regarding attribute joins in a model: When I try to perform an attribute join within a model, I cannot select the join fields (even though the process works perfectly in Whitebox)!
Thanks,
Geguil