class ViewModel::ActiveRecord::Cache

def initialize(viewmodel_class, cache_group: nil)

If cache_group: is specified, it must be a group of a single key: `:id` 
def initialize(viewmodel_class, cache_group: nil)
  @viewmodel_class = viewmodel_class
  @cache_group = cache_group || create_default_cache_group
  @migrated_cache_group = @cache_group.register_child_group(:migrated, :version)
  # /viewname/:id/viewname-currentversion
  @cache = @cache_group.register_cache(cache_name)
  # /viewname/:id/migrated/:oldversion/viewname-currentversion
  @migrated_cache = @migrated_cache_group.register_cache(cache_name)
end