discourse/app/models/concerns/has_custom_fields.rb

module HasCustomFields
  extend ActiveSupport::Concern

  module Helpers

    def self.append_field(target, key, value, types)
      if target.has_key?(key)
        target[key] = [target[key]] if !target[key].is_a? Array
        target[key] << cast_custom_field(key, value, types)
      else
        target[key] = cast_custom_field(key, value, types)
      end
    end

    CUSTOM_FIELD_TRUE ||= ['1', 't', 'true', 'T', 'True', 'TRUE'].freeze

    def self.get_custom_field_type(types, key)
      return unless types

      sorted_types = types.keys.select { |k| k.end_with?("*") }
                               .sort_by(&:length)
                               .reverse

      sorted_types.each do |t|
        return types[t] if key =~ /^#{t}/i
      end

      types[key]
    end

    def self.cast_custom_field(key, value, types)
      return value unless type = get_custom_field_type(types, key)

      case type
        when :boolean then !!CUSTOM_FIELD_TRUE.include?(value)
        when :integer then value.to_i
        when :json    then ::JSON.parse(value)
      else
        value
      end
    end
  end

  included do
    has_many :_custom_fields, dependent: :destroy, :class_name => "#{name}CustomField"
    after_save :save_custom_fields

    attr_accessor :preloaded_custom_fields

    # To avoid n+1 queries, use this function to retrieve lots of custom fields in one go
    # and create a "sideloaded" version for easy querying by id.
    def self.custom_fields_for_ids(ids, whitelisted_fields)
      klass = "#{name}CustomField".constantize
      foreign_key = "#{name.underscore}_id".to_sym

      result = {}

      return result if whitelisted_fields.blank?

      klass.where(foreign_key => ids, :name => whitelisted_fields)
           .pluck(foreign_key, :name, :value).each do |cf|
        result[cf[0]] ||= {}
        append_custom_field(result[cf[0]], cf[1], cf[2])
      end

      result
    end

    def self.append_custom_field(target, key, value)
      HasCustomFields::Helpers.append_field(target, key, value, @custom_field_types)
    end

    def self.register_custom_field_type(name, type)
      @custom_field_types ||= {}
      @custom_field_types[name] = type
    end

    def self.preload_custom_fields(objects, fields)
      if objects.present?
        map = {}

        empty = {}
        fields.each do |field|
          empty[field] = nil
        end

        objects.each do |obj|
          map[obj.id] = obj
          obj.preloaded_custom_fields = empty.dup
        end

        fk = (name.underscore << "_id")

        "#{name}CustomField".constantize
          .where("#{fk} in (?)", map.keys)
          .where("name in (?)", fields)
          .pluck(fk, :name, :value).each do |id, name, value|

            preloaded = map[id].preloaded_custom_fields

            if preloaded[name].nil?
              preloaded.delete(name)
            end

            HasCustomFields::Helpers.append_field(preloaded, name, value, @custom_field_types)
        end

      end
    end
  end

  def reload(options = nil)
    clear_custom_fields
    super
  end

  def custom_field_preloaded?(name)
    @preloaded_custom_fields && @preloaded_custom_fields.key?(name)
  end

  def clear_custom_fields
    @custom_fields = nil
    @custom_fields_orig = nil
  end

  class PreloadedProxy
    def initialize(preloaded)
      @preloaded = preloaded
    end

    def [](key)
      if @preloaded.key?(key)
        @preloaded[key]
      else
        # for now you can not mix preload an non preload, it better just to fail
        raise StandardError, "Attempting to access a non preloaded custom field, this is disallowed to prevent N+1 queries."
      end
    end
  end

  def custom_fields

    if @preloaded_custom_fields
      return @preloaded_proxy ||= PreloadedProxy.new(@preloaded_custom_fields)
    end

    @custom_fields ||= refresh_custom_fields_from_db.dup
  end

  def custom_fields=(data)
    custom_fields.replace(data)
  end

  def custom_fields_clean?
    # Check whether the cached version has been changed on this model
    !@custom_fields || @custom_fields_orig == @custom_fields
  end

  def save_custom_fields(force=false)
    if force || !custom_fields_clean?
      dup = @custom_fields.dup

      array_fields = {}

      _custom_fields.each do |f|
        if dup[f.name].is_a? Array
          # we need to collect Arrays fully before we can compare them
          if !array_fields.has_key?(f.name)
            array_fields[f.name] = [f]
          else
            array_fields[f.name] << f
          end
        elsif dup[f.name].is_a? Hash
          if dup[f.name].to_json != f.value
            f.destroy
          else
            dup.delete(f.name)
          end
        else
          if dup[f.name] != f.value
            f.destroy
          else
            dup.delete(f.name)
          end
        end
      end

      # let's iterate through our arrays and compare them
      array_fields.each do |field_name, fields|
        if fields.length == dup[field_name].length && fields.map(&:value) == dup[field_name]
          dup.delete(field_name)
        else
          fields.each(&:destroy)
        end
      end

      dup.each do |k,v|
        if v.is_a? Array
          v.each { |subv| _custom_fields.create(name: k, value: subv) }
        elsif v.is_a? Hash
          _custom_fields.create(name: k, value: v.to_json)
        else
          _custom_fields.create(name: k, value: v)
        end
      end

      refresh_custom_fields_from_db
    end
  end

  protected

  def refresh_custom_fields_from_db
    target = Hash.new
    _custom_fields.pluck(:name,:value).each do |key, value|
      self.class.append_custom_field(target, key, value)
    end
    @custom_fields_orig = target
    @custom_fields = @custom_fields_orig.dup
  end

end