validate district_nces_id for uniqueness and normalize both new fields

Author: Mohamed Ali

app/models/school.rb

@@ -17,6 +17,7 @@ class School < ApplicationRecord
   validates :municipality, presence: true
   validates :country_code, presence: true, inclusion: { in: ISO3166::Country.codes }
   validates :reference, uniqueness: { case_sensitive: false, allow_nil: true }, presence: false
+    validates :district_nces_id, uniqueness: { allow_nil: true }, presence: false
   validates :creator_id, presence: true, uniqueness: true
   validates :creator_agree_authority, presence: true, acceptance: true
   validates :creator_agree_terms_and_conditions, presence: true, acceptance: true
@@ -32,6 +33,7 @@ class School < ApplicationRecord
   validate :code_cannot_be_changed
 
   before_validation :normalize_reference
+  before_validation :normalize_district_fields
 
   before_save :format_uk_postal_code, if: :should_format_uk_postal_code?
 
@@ -94,6 +96,12 @@ def normalize_reference
     self.reference = nil if reference.blank?
   end
 
+  # Ensure district fields are nil, not empty strings
+  def normalize_district_fields
+    self.district_name = nil if district_name.blank?
+    self.district_nces_id = nil if district_nces_id.blank?
+  end
+
   def verified_at_cannot_be_changed
     errors.add(:verified_at, 'cannot be changed after verification') if verified_at_was.present? && verified_at_changed?
   end