def write_all(key, data = nil, parameters = {}, conditions = {})
      @stores.map {|s| s.write_all(key, data, parameters, conditions)}.all?
    end
def write_all(key, data = nil, parameters = {}, conditions = {})
      @stores.map {|s| s.write_all(key, data, parameters, conditions)}.all?
    end
persists the data to all context stores.
 returns nil if none of the stores were able to persist the data.
 returns true if at least one write was successful.