update cascading select field by look up table

[Negar Mousavi]

hey guys
im trying to update cascading field by look up table, i have already do that reverse.

I have the field department which is a cascading select list and it has 2level, when I have the value for example x,y i can write this as {null=x, 1=y} and it returns the column manager and put that in another field.

now i want to do it reverse first i have the user, as the reporter and then it should match it with the column department and read the {null=x, 1=y}  and update the field, i do the same thing in the post function, but with no errors the transition just doesnt happen, is it because its impossible to fill a cascading field through look up table or the syntax is just for reading the field value not writing?

thanks