Calculating one cell in an attribute table in ModelBuilder

Question

There are two point feature classes--let's call them Established_points and Newcomer. Established_points has, among others, two attribute fields called (for example) ALL_SIGHTINGS and CONFIRMED_SIGHTINGS. In ModelBuilder, I need to append Newcomer into Established_points. Because Newcomer doesn't have the two fields mentioned above, the values in those fields for that record in Established_points will be Null after the appending. I need to calculate the values for those fields, however (based on something else in my model).

What is the best way to go about this? After appending the two feature classes, should I use some kind of cursor, perhaps, to go through the ALL_SIGHTINGS and CONFIRMED_SIGHTINGS fields and calculate any cells that are Null? (There should only be that one cell for each field.) Or is there some easier way, or some workaround with which to avoid the issue altogether?

Answer 1

In this case, anyway, I decided that I need to calculate all fields for each of the two feature classes individually, before they are merged. Then, when merging the two, I will use field mapping if necessary (although, if the fields have the same name, they will be merged into one field even without field mapping, as I've discovered).