Question

我正在使用vavr和jOOQ，这是最近出现的两个很棒的库，允许我们在常规Java服务器应用程序中使用功能性方言。

我正在尝试使用jOOQ，这相当于SQL的select count（*）。

查询是通过以下方式形成的：

 ResultQuery query = dsl.selectCount()
                .from(Tables.SH_PLAYER_REPORT)
                .join(Tables.SH_PLAYERS)
                .on(Tables.SH_PLAYERS.PLAYER_ID.eq(Tables.SH_PLAYER_REPORT.PLAYER_ID))
                .join(Tables.SH_LOCATION)
                .on(Tables.SH_LOCATION.LOCATION_ID.eq(Tables.SH_PLAYERS.LOCATION))
                .and(Tables.SH_PLAYER_REPORT.START_ON.ge(Timestamp.from(fromWhenInUTCInstant)))
                .and(Tables.SH_PLAYER_REPORT.START_ON.le(Timestamp.from(toWhenInUTCInstant)))
                .and(Tables.SH_LOCATION.LOCATION_ID.eq(criteriaAllFieldsTeam.getLocation_id()));

jOOQ的生成器运行良好，这里没有任何类型不匹配的情况。因此，我想查询的格式正确。

然后，我正在使用vavr的Try，因此：

Optional<Integer> mayBeCount = Optional.empty();

try (final Connection cn = this.ds.getConnection()) {

    DSLContext dsl = DSL.using(cn, this.dialect);

    Try<Integer> countFromDBAttempted =
               Try
               .of(() -> prepareCountOfGamesPlayedQuery(dsl,criteriaAllFieldsTeam))
               .map(e -> e.fetchOne(0, Integer.class)) // Here's the problem!
               .onFailure(e -> logger.warning(String.format("Count Of Games Played, status=Failed, reason={%s}",e.getMessage())));

           mayBeCount = (countFromDBAttempted.isFailure() ? Optional.empty() : Optional.of(countFromDBAttempted.getOrElse(0)));

  } catch (SQLException ex) {

    logger.warning(
         String.format("DB(jOOQ): Failed, counting games played, using criteria {%s},reason={%s}",criteriaAllFieldsTeam.toString(),ex.getMessage()));
  }

  return (mayBeCount);

尽管我提供了帮助，但编译器无法通过描述目标类型来推断字段的类型： Integer.class ！

../ReportByTeamRecordProducerImpl.java:66: error: incompatible types: Try<Object> cannot be converted to Try<Integer>
.onFailure(e -> logger.warning(String.format("Count Of Games Played, status=Failed, reason={%s}",e.getMessage())));
                         ^

毫不奇怪，当我强制类型时，代码运行得很好。我只是在编译器认为.. er ..令人反感的那一行上引入一个显式强制转换！

Try<Integer> countFromDBAttempted =
   Try
   // The following function returns the ResultQuery shown above
   .of(() -> prepareCountOfGamesPlayedQuery(dsl,criteriaAllFieldsTeam))
   // Casting below, because of some incompatibility between vavr and jOOQ
  .map(e -> ((Integer) e.fetchOne(0, Integer.class)))
  .onFailure(e -> logger.warning(String.format("Count Of Games Played, status=Failed, reason={%s}",e.getMessage())));

根据对jOOQ库的理解，尤其是@ explanation的LukasEder，我尝试了几种其他方法。

到目前为止，我还没有尝试过引入 Converter ，因为对于单个字段值，在我看来这似乎是不必要的！但是，如果那样的话，那么我想暗示一下。

响应@ LukasEder：

private ResultQuery prepareCountOfGamesPlayedQuery(DSLContext dsl, CriteriaAllFieldsTeam criteriaAllFieldsTeam) {

        Instant fromWhenInUTCInstant =
                convertToDBCompatibleInstantUTC(
                        criteriaAllFieldsTeam.getDate_range().getFromWhen(),
                        criteriaAllFieldsTeam.getDate_range().getInTimeZone());

        Instant toWhenInUTCInstant =
                convertToDBCompatibleInstantUTC(
                        criteriaAllFieldsTeam.getDate_range().getToWhen(),
                        criteriaAllFieldsTeam.getDate_range().getInTimeZone());

        ResultQuery query = dsl.selectCount()
                .from(Tables.SH_PLAYER_REPORT)
                .join(Tables.SH_PLAYERS)
                .on(Tables.SH_PLAYERS.PLAYER_ID.eq(Tables.SH_PLAYER_REPORT.PLAYER_ID))
                .join(Tables.SH_LOCATION)
                .on(Tables.SH_LOCATION.LOCATION_ID.eq(Tables.SH_PLAYERS.LOCATION))
                .and(Tables.SH_PLAYER_REPORT.START_ON.ge(Timestamp.from(fromWhenInUTCInstant)))
                .and(Tables.SH_PLAYER_REPORT.START_ON.le(Timestamp.from(toWhenInUTCInstant)))
                .and(Tables.SH_LOCATION.LOCATION_ID.eq(criteriaAllFieldsTeam.getLocation_id()));

        return (query);
    }

接下来，卢卡斯（Lukas）的推特，我以这种方式修改了该方法：

private ResultQuery<Record1<Integer>> prepareCountOfGamesPlayedQuery(DSLContext dsl, CriteriaAllFieldsTeam criteriaAllFieldsTeam) {

        Instant fromWhenInUTCInstant =
                convertToDBCompatibleInstantUTC(
                        criteriaAllFieldsTeam.getDate_range().getFromWhen(),
                        criteriaAllFieldsTeam.getDate_range().getInTimeZone());

        Instant toWhenInUTCInstant =
                convertToDBCompatibleInstantUTC(
                        criteriaAllFieldsTeam.getDate_range().getToWhen(),
                        criteriaAllFieldsTeam.getDate_range().getInTimeZone());

        ResultQuery<Record1<Integer>> query = dsl.selectCount()
                .from(Tables.SH_PLAYER_REPORT)
                .join(Tables.SH_PLAYERS)
                .on(Tables.SH_PLAYERS.PLAYER_ID.eq(Tables.SH_PLAYER_REPORT.PLAYER_ID))
                .join(Tables.SH_LOCATION)
                .on(Tables.SH_LOCATION.LOCATION_ID.eq(Tables.SH_PLAYERS.LOCATION))
                .and(Tables.SH_PLAYER_REPORT.START_ON.ge(Timestamp.from(fromWhenInUTCInstant)))
                .and(Tables.SH_PLAYER_REPORT.START_ON.le(Timestamp.from(toWhenInUTCInstant)))
                .and(Tables.SH_LOCATION.LOCATION_ID.eq(criteriaAllFieldsTeam.getLocation_id()));

        return (query);
    }

..，现在世界再次和平！

谢谢，卢卡斯！

Answer 1

给出您到目前为止提供的代码，并假设没有错字，这可能是由于您对ResultQuery的原始类型引用造成的。改用ResultQuery<?>或ResultQuery<Record1<Integer>>。

除非确实需要，否则请勿使用原始类型。而你可能不会。

类型推断似乎使vavr的Try在jOOQ的fetchOne（）函数上起作用

1 个答案: