Keyset positionFunction does not retain directional state and uses position of one-off

[quaff]

spring-data-jpa/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/ScrollDelegate.java

Line 87 in 8cae8cd

T object = result.get(value);

We must use window.positionAt(1) instead of window.positionAt(0) if we want position at the begin of window, we should call getResultWindow() first.

spring-data-jpa/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/ScrollDelegate.java

Line 90 in 8cae8cd

return ScrollPosition.forward(keys);

The direction always be FORWARD, it should be BACKWARD if the original direction is BACKWARD.

[mp911de]

Scrolling forward after retrieving a window is by design as the Window.next() and all scroll position methods suggest forward scrolling. Reversing is rather a by-product and not reflected within the consuming API.

[quaff]

It's weird that I cannot using BACKWARD scrolling for iteration.
My test case is broken if scrollDirection is BACKWARD.

	@ParameterizedTest
	@MethodSource("provideParameters")
	void keysetScrolling(Sort.Direction sortDirection, ScrollPosition.Direction scrollDirection) {

		List<List<TestEntity>> contents = new ArrayList<>();

		String propertyName = "index";
		Object anchor = null;
		Sort sort = Sort.by(sortDirection, propertyName);

		Map<String, ?> keys = anchor != null ? Map.of(propertyName, anchor) : Map.of();
		ScrollPosition pos = ScrollPosition.of(keys, scrollDirection);
		while (true) {
			ScrollPosition spToUse = pos;
			Window<TestEntity> window = this.repository.findBy((root, query, cb) -> {
				return null;
			}, q -> q.limit(pageSize).sortBy(sort).scroll(spToUse));
			contents.add(window.getContent());
			if (!window.hasNext()) {
				break;
			}
			pos = window.positionAt(((KeysetScrollPosition) pos).scrollsForward() ? window.size() - 1 : 0);
		}
		// asserts
	}

	private static Stream<Arguments> provideParameters() {
		return cartesian(Sort.Direction.class, ScrollPosition.Direction.class);
	}

	private static Stream<Arguments> cartesian(Class<? extends Enum<?>> enumA, Class<? extends Enum<?>> enumB) {
		return Stream.of(enumA.getEnumConstants())
			.flatMap(a -> Stream.of(enumB.getEnumConstants()).map(b -> Arguments.of(a, b)));
	}