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julgus avatar julgus commented on July 17, 2024

This problem seems to stem from several places. Firstly, the criteria merger should not continue merging operations after encountering an anonymous lambda. At its current state, it merges any operations that contain a JPAStreamer predicate, regardless of the ordering in the pipeline.

After fixing that, a similar test still fails:

        try (StreamSupplier<Film> supplier = jpaStreamer.createStreamSupplier(Film.class)) {
            final List<String> actual = supplier.stream()
                    .filter(f -> f.getLength() > 120)
                    .sorted(Film$.length)
                    .filter(Film$.title.startsWith("A"))
                    .map(Film$.title)
                    .limit(10)
                    .collect(Collectors.toList());

            final List<String> expected = supplier.stream()
                    .filter(f -> f.getLength() > 120)
                    .sorted(Comparator.comparing(Film::getLength))
                    .map(Film::getTitle)
                    .filter(title -> title.startsWith("A"))
                    .limit(10)
                    .collect(Collectors.toList());

            assertEquals(expected, actual);
        }

In this case, reordering rules allow the first Stream to be optimized as:

            final List<String> actual = supplier.stream()
                    .sorted(Film$.length)
                    .filter(Film$.title.startsWith("A"))
                    .filter(f -> f.getLength() > 120)
                    .map(Film$.title)
                    .limit(10)
                    .collect(Collectors.toList());

This means we can merge the sort and the filter on the title into the query without any issues. However, the limit is also applied on the DB side, limiting the results to 10 before the filter length > 120 is executed. Due to the sorting operation, the 10 shortest films are returned and none of them will match the criteria length > 120.

from jpa-streamer.

julgus avatar julgus commented on July 17, 2024

Another example is this test:

            final List<String> actual = supplier.stream()
                    .filter(Film$.title.startsWith("A"))
                    .skip(10)
                    .filter(f -> f.getLength() > 120)
                    .sorted(Film$.length)
                    .limit(10)
                    .map(Film$.title)
                    .collect(Collectors.toList());

Here the SORTED is merged even though the SKIP precedes it. As SQL always applies SKIPS and LIMITS to the end of all other operations, we cannot merge this sort as it will change what entities are skipped.

from jpa-streamer.

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