code: public M findByIdLoadColumns(Object idValue, String columns) {
  		return findByIdLoadColumns(new Object[]{idValue}, columns);
  	}
docs: Find model by id and load specific columns only.
  <pre>
  Example:
  User user = User.dao.findByIdLoadColumns(123, "name, age");
  </pre>
  @param idValue the id value of the model
  @param columns the specific columns to load