module ActiveRecord::Integration

def cache_version

+false+.
Note, this method will return nil if ActiveRecord::Base.cache_versioning is set to

cache_version, but this method can be overwritten to return something else.
a recyclable caching scheme. By default, the #updated_at column is used for the
Returns a cache version that can be used together with the cache key to form 
def cache_version
  return unless cache_versioning
  if has_attribute?("updated_at")
    timestamp = updated_at_before_type_cast
    if can_use_fast_cache_version?(timestamp)
      raw_timestamp_to_cache_version(timestamp)
    elsif timestamp = updated_at
      timestamp.utc.to_fs(cache_timestamp_format)
    end
  elsif self.class.has_attribute?("updated_at")
    raise ActiveModel::MissingAttributeError, "missing attribute 'updated_at' for #{self.class}"
  end
end