Type inference seems to fail vavr's Try works on jOOQ's fetchOne() function

Question

I am using vavr and jOOQ, two fantastic libraries to have come out in the recent times, allowing us to use functional dialects in regular Java server applications.

I am trying to get using jOOQ, what is equivalent of SQL's select count (*).

The query is formed this way:

 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's generator has worked perfectly, and there isn't any type-mismatch here. So, I guess, the query is correctly formed.

Then, I am using vavr's Try, thus:

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);

The compiler fails to infer the type of the field, despite the help I give to it, by describing the target type: 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())));
                         ^

Unsurprisingly, when I coerce the type, then the code runs perfectly fine. I just the introduce an explicit cast, at the line that the compiler considers .. er .. distasteful!

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())));

I have tried with a couple of other ways, based upon my understanding of jOOQ library and especially, this explanation by @LukasEder.

What I haven't tried so far, is to introduce a Converter, because for a single field value, that seems to be unnecessary, to my eyes! However, if that's the way, then I would like to have a hint.

In response to @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);
    }

Following, Lukas' nudge, I have modified the method this way:

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);
    }

.. and, now peace again prevails in the world!

Thanks, Lukas!

Could you please point us to the public javadoc of the `fetchOne` method you are using? — Nándor Előd Fekete, Dec 13 '18 at 12:09
Can you show the exact definition of `prepareCountOfGamesPlayedQuery` — Lukas Eder, Dec 13 '18 at 13:12
@NándorElődFekete, I was referring to this: http://www.jooq.org/javadoc/3.11.x/org/jooq/ResultQuery.html — Nirmalya, Dec 13 '18 at 15:17

score 6 · Accepted Answer · answered Dec 13 '18 at 13:10

6

Given the code you've provided so far, and assuming there's no typo, this is probably caused because of your raw type reference to ResultQuery. Use ResultQuery<?> or ResultQuery<Record1<Integer>> instead.

Never use raw types, unless you really have to. And you probably don't.

answered Dec 13 '18 at 13:10

Lukas Eder

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Lukas, your guess is correct. I have been using a raw type reference to ResultQuery. For some reason, I assumed that the type would be inferred (may be an unwholesome hang-over from the Scala world). For the sake completeness, I have updated the original question, with the modified method. – Nirmalya Dec 13 '18 at 15:27
1

@Nirmalya: What did you update? You're still using a raw type. Don't use a raw type. It messes up all of Java's generics and type inference with unholy rules that no one can decipher. Just have your method return `ResultQuery>` (and turn on compiler warnings, and fix all the other raw type references) :) – Lukas Eder Dec 13 '18 at 15:29
Sorry, I was a tad slower than you! You had to type in those extra words! :-/ – Nirmalya Dec 13 '18 at 15:30
1

@Nirmalya: I see, no worries :) Notice, you don't have to put an answer / explanation in your question. Accepting the right answer is sufficient here on Stack Overflow – Lukas Eder Dec 13 '18 at 15:34
Yes, I know. But, I thought I must atone for the silly mistake, in some manner! :-) – Nirmalya Dec 13 '18 at 15:36

Type inference seems to fail vavr's Try works on jOOQ's fetchOne() function

1 Answers1