Rake task that scans all Rails models for orphaned belong_to associations (Rails 3.2 or higher)

orphaned_check.rake

task :orphaned_check => :environment do

  Dir[Rails.root.join('app/models/*.rb').to_s].each do |filename|
    klass = File.basename(filename, '.rb').camelize.constantize
    next unless klass.ancestors.include?(ActiveRecord::Base)

    orphanes = Hash.new

    klass.reflect_on_all_associations(:belongs_to).each do |belongs_to|
      assoc_name, field_name = belongs_to.name.to_s, belongs_to.foreign_key.to_s

      if belongs_to.options[:polymorphic]
        foreign_type_field = field_name.gsub('_id', '_type')
        foreign_types = klass.unscoped.select("DISTINCT(#{foreign_type_field})")
        foreign_types = foreign_types.collect { |r| r.send(foreign_type_field) }

        foreign_types.sort.each do |foreign_type|
          related_sql = foreign_type.constantize.unscoped.select(:id).to_sql

          finder = klass.unscoped.select(:id).where("#{foreign_type_field} = '#{foreign_type}'")
          finder.where("#{field_name} IS NOT NULL AND #{field_name} NOT IN (#{related_sql})").each do |orphane|
            orphanes[orphane] ||= Array.new
            orphanes[orphane] << [assoc_name, field_name]
          end
        end
      else
        class_name = (belongs_to.options[:class_name] || assoc_name).classify
        related_sql = class_name.constantize.unscoped.select(:id).to_sql

        finder = klass.unscoped.select(:id)
        finder.where("#{field_name} IS NOT NULL AND #{field_name} NOT IN (#{related_sql})").each do |orphane|
          orphanes[orphane] ||= Array.new
          orphanes[orphane] << [assoc_name, field_name]
        end
      end
    end

    orphanes.sort_by { |record, data| record.id }.each do |record, data|
      data.sort_by(&:first).each do |assoc_name, field_name|
        puts "#{record.class.name}##{record.id} #{field_name} is present, but #{assoc_name} doesn't exist"
      end
    end
  end

end

this is great!

a version of this script that handles namespaced classes and allows deleting via a command line option:

https://gist.github.com/hooverlunch/6275940