Add migration to backfill the district_name field for US schools where empty

Author: jamiebenstead

db/migrate/20260121103308_backfill_district_name_for_us_schools.rb

@@ -0,0 +1,15 @@
+class BackfillDistrictNameForUsSchools < ActiveRecord::Migration[7.2]
+  def up
+    School
+      .where(country_code: "US")
+      .where("district_name IS NULL OR BTRIM(district_name) = ''")
+      .update_all(district_name: "District Unknown")
+  end
+
+  def down
+    School
+      .where(country_code: "US")
+      .where(district_name: "District Unknown")
+      .update_all(district_name: nil)
+  end
+end