ForeignKey fk;
// copy where conditions into new update that nulls the fk
row = (PrimaryRow) edge.getTo();
update = new PrimaryRow(row.getTable(), Row.ACTION_UPDATE, null);
row.copyInto(update, true);
if (edge.getUserObject() instanceof ForeignKey) {
fk = (ForeignKey) edge.getUserObject();
update.setForeignKey(fk, row.getForeignKeyIO(fk), null);
} else
update.setNull((Column) edge.getUserObject());