preloader_for

# File activerecord/lib/active_record/associations/preloader.rb, line 184
      def preloader_for(reflection, owners, rhs_klass)
        return NullPreloader unless rhs_klass

        if owners.first.association(reflection.name).loaded?
          return AlreadyLoaded
        end
        reflection.check_preloadable!

        case reflection.macro
        when :has_many
          reflection.options[:through] ? HasManyThrough : HasMany
        when :has_one
          reflection.options[:through] ? HasOneThrough : HasOne
        when :belongs_to
          BelongsTo
        end
      end