def build_nodes
      value = _target_column

      for key in _key_chain
        value[key] = {} unless value[key]
        value = value[key]
      end
    end
def build_nodes
      value = _target_column

      for key in _key_chain
        value[key] = {} unless value[key]
        value = value[key]
      end
    end
Call this method before set any values