Add comments, improve performace etc.

Author: yzhoubk

db/migrate/20250930220504_update_term_item_relation.rb

@@ -1,3 +1,4 @@
+# Migration to reassign items with the term "After 1999" to a newly categorized term.
 class UpdateTermItemRelation < ActiveRecord::Migration[7.0]
   def up
     facet = Facet.find_by!(name: 'Decade')
@@ -25,16 +26,16 @@ def up
     end
 
     if invalid_items.any?
-      Rails.logger.warn("Skipped #{invalid_items.size} items due to invalid or missing dates. Example: #{invalid_items.first(10).map { |i| "ID #{i[:id]}: '#{i[:date]}'" }.join(', ')}")
+      Rails.logger.warn("Skipped #{invalid_items.size} items due to invalid or missing dates. Example: #{invalid_items.first(5).map { |i| "ID #{i[:id]}: '#{i[:date]}'" }.join(', ')}")
     end
   end
 
   def down
     facet = Facet.find_by!(name: 'Decade')
     target_term = Term.find_by!(facet: facet, value: 'After 1999')
-    move_term_back_to_item(facet,  '2000-2009', target_term)
-    move_term_back_to_item(facet, '2010-2019', target_term)
-    move_term_back_to_item(facet, 'After 2020', target_term)
+    revert_term_assignment(facet,  '2000-2009', target_term)
+    revert_term_assignment(facet, '2010-2019', target_term)
+    revert_term_assignment(facet, 'After 2020', target_term)
   end
 
   private
@@ -43,27 +44,28 @@ def integer_year(val)
     return nil if val.nil?
 
     # Try direct integer conversion
+    year = nil
     begin
-      return Integer(val)
+      year = Integer(val)
     rescue ArgumentError, TypeError
       # Try to extract year from common date formats (e.g., "YYYY-MM-DD", "YYYY/MM/DD")
       if val.is_a?(String)
         if val =~ /\A(\d{4})[-\/]/
-          return $1.to_i
+          year = $1.to_i
         end
       end
-      return nil
     end
+    return year
   end
 
   # Reassigns an item from the origin term to the target term, and removes the origin term from the item.
   def re_assign_term_to_item(item, origin_term, target_term)
-    item.terms << target_term unless item.terms.include?(target_term)
+    item.terms << target_term
     item.terms.delete(origin_term)
   end
 
   # Rolls back term assignment from origin_term_value to target_term for all items.
-  def move_term_back_to_item(facet, origin_term_value, target_term)
+  def revert_term_assignment(facet, origin_term_value, target_term)
     origin_term = Term.find_by!(facet: facet, value: origin_term_value)
     origin_term.items.find_each do |item|
       re_assign_term_to_item(item, origin_term, target_term)