code: private <T> Observable<T> executeOnce(final List<Parameter> params,
              ResultSetMapper<? extends T> function) {
          return QuerySelectOnSubscribe.execute(this, params, function)
                  .subscribeOn(context.scheduler());
      }
docs: Returns an Observable of the results of pushing one set of parameters
  through a select query.
  
  @param params
  one set of parameters to be run with the query
  @return