JoinPredicates don't have correct types

[colestew]

When performing a join, the predicates are typed as HgBiPredicate<Object, Object> instead of the actual types of the fields being joined on. Obviously this needs to be changed. It's likely going to be difficult to fix this problem as it will require some substantial refactorings.

[colestew]

Observe the following:

        HgDB.join(new JoinPredicate(
                PersonTable.on.birthday(),
                PersonTable.as(PERSON_ALIAS).on.birthday(),
                (HgBiPredicate<Date, Date>)(d1, d2) -> {
                    Calendar.getInstance().setTime(d1);
                    int d1Month = Calendar.getInstance().get(Calendar.MONTH);
                    Calendar.getInstance().getInstance().setTime(d2);
                    int d2Month = Calendar.getInstance().get(Calendar.MONTH);
                    return d1Month == d2Month;
                }
        ));

Eclipse does not need the cast to work correctly, however IntelliJ does. Also, IntelliJ claims this cast is redundant, but removing it breaks the statement. This could just be an intelliJ problem.

[dilijev]

Regardless of IntelliJ's warning/error, does it compile in Gradle?

[dilijev]

We might do this to help the compiler figure out the types:

public static <T1, T2> HgPolyTupleStream join(
            HgTupleStream a,
            HgTupleStream b,
            HgBiPredicate<T1, T2> relation) {
        return join(new JoinPredicate(a, b, relation));
    }

[dilijev]

We might also do something like this to help advertise all of the relevant types, as long as it doesn't increase the complexity of the user-facing API.

public static HgPolyTupleStream join(
            HgTupleStream<T1, F1> a, // or just <F1>
            HgTupleStream<T2, F2> b, // or just <F2>
            HgBiPredicate<F1, F2> relation) {
        return join(new JoinPredicate(a, b, relation));
    }

Where each HgTupleStream advertises the type and field it is joining on. T1 is the type of the containing class and F1 is the type of the field, for each parameter.

[dilijev]

Also you can give types to the parameters of a lambda directly:

        HgDB.join(new JoinPredicate(
                PersonTable.on.birthday(),
                PersonTable.as(PERSON_ALIAS).on.birthday(),
                (Date d1, Date d2) -> {
                    cal1.setTime(d1);
                    int d1Month = cal1.get(Calendar.MONTH);
                    cal2.setTime(d2);
                    int d2Month = cal2.get(Calendar.MONTH);
                    return d1Month == d2Month;
                }
        ))