code: private Func1<List<Parameter>, Observable<T>> executeOnce() {
          return new Func1<List<Parameter>, Observable<T>>() {
              @Override
              public Observable<T> call(final List<Parameter> params) {
                  if (jdbcQuery.sql().equals(QueryUpdateOnSubscribe.BEGIN_TRANSACTION)) {
                      context.beginTransactionSubscribe();
                  }
                  Observable<T> result = createUpdate(params).subscribeOn(context.scheduler());
                  if (jdbcQuery.sql().equals(QueryUpdateOnSubscribe.COMMIT)
                          || jdbcQuery.sql().equals(QueryUpdateOnSubscribe.ROLLBACK))
                      context.endTransactionSubscribe();
                  return result;
              }
          };
      }
docs: Returns a {@link Func1} that itself returns the results of pushing
  parameters through an update query.
  
  @param query
  @return