code: public void addAction(String firstName, String lastName, String actionType,
        String actionValue) {
      // Create a new UserActionsModel, and add a new actions map to it with a
      // single action value. Even if one exists in this row, since it has a lone
      // keyAsColumn field, it won't remove any actions that already exist in the
      // actions column family.
      UserActionsModel actionsModel = UserActionsModel.newBuilder()
          .setLastName(lastName).setFirstName(firstName)
          .setActions(new HashMap<String, String>()).build();
      actionsModel.getActions().put(actionType, actionValue);
  
      // Perform the put.
      userActionsDao.put(actionsModel);
    }
docs: Add an action to the user profile.
  
  This method demonstrates how we can use a keyAsColumn map field (the
  actions field of the UserActionsModel) to add values to the map without
  having to do a get/update/put operation. When doing the put, it won't
  remove columns that exist in the row that aren't in the new map we are
  putting. It will just add the additional columns we are now putting to the
  row.
  
  @param firstName
  The first name of the user we are updating
  @param lastName
  The last name of the user we are updating
  @param actionType
  A string representing the action type which is the key of the map
  @param actionValue
  A string representing the action value.