class ActiveRecord::FixtureSet::ClassCache

def [](fs_name)
  @class_names.fetch(fs_name) {
    klass = default_fixture_model(fs_name, @config).safe_constantize
    insert_class(@class_names, fs_name, klass)
  }
end

def default_fixture_model(fs_name, config)
  ActiveRecord::FixtureSet.default_fixture_model_name(fs_name, config)
end

def initialize(class_names, config)
  @class_names = class_names.stringify_keys
  @config      = config
  # Remove string values that aren't constants or subclasses of AR
  @class_names.delete_if { |k,klass|
    unless klass.is_a? Class
      klass = klass.safe_constantize
      ActiveSupport::Deprecation.warn("The ability to pass in strings as a class name will be removed in Rails 4.2, consider using the class itself instead.")
    end
    !insert_class(@class_names, k, klass)
  }
end

def insert_class(class_names, name, klass)
  # We only want to deal with AR objects.
  if klass && klass < ActiveRecord::Base
    class_names[name] = klass
  else
    class_names[name] = nil
  end
end