Redmine/db/migrate/20210801211024_remove_orphaned_user_custom_values.rb

class RemoveOrphanedUserCustomValues < ActiveRecord::Migration[6.1]
  def up
    user_custom_field_ids = CustomField.where(field_format: 'user').ids
    if user_custom_field_ids.any?
      user_ids = Principal.ids
      CustomValue.
        where(custom_field_id: user_custom_field_ids).
        where.not(value: [nil, ''] + user_ids).
        delete_all
    end
  end
end