Add support for findBy(…) using Querydsl Predicate that returns a Slice.

Closes #3764

Author: mp911de

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

@@ -28,7 +28,6 @@
 import org.springframework.dao.InvalidDataAccessApiUsageException;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
-import org.springframework.data.domain.Slice;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.jpa.domain.Specification;
 import org.springframework.data.repository.query.FluentQuery;
@@ -182,25 +181,13 @@ default SpecificationFluentQuery<T> project(String... properties) {
 		@Override
 		SpecificationFluentQuery<T> project(Collection<String> properties);
 
-		/**
-		 * Get a slice of matching elements for {@link Pageable} by requesting {@code Pageable#getPageSize() + 1} elements.
-		 *
-		 * @param pageable the pageable to request a paged result, can be {@link Pageable#unpaged()}, must not be
-		 *          {@literal null}. The given {@link Pageable} will override any previously specified {@link Sort sort} if
-		 *          the {@link Sort} object is not {@link Sort#isUnsorted()}. Any potentially specified {@link #limit(int)}
-		 *          will be overridden by {@link Pageable#getPageSize()}.
-		 * @return
-		 */
-		Slice<T> slice(Pageable pageable);
-
 		/**
 		 * Get a page of matching elements for {@link Pageable} and provide a custom {@link Specification count
 		 * specification}.
 		 *
 		 * @param pageable the pageable to request a paged result, can be {@link Pageable#unpaged()}, must not be
-		 *          {@literal null}. The given {@link Pageable} will override any previously specified {@link Sort sort} if
-		 *          the {@link Sort} object is not {@link Sort#isUnsorted()}. Any potentially specified {@link #limit(int)}
-		 *          will be overridden by {@link Pageable#getPageSize()}.
+		 *          {@literal null}. The given {@link Pageable} will override any previously specified {@link Sort sort}.
+		 *          Any potentially specified {@link #limit(int)} will be overridden by {@link Pageable#getPageSize()}.
 		 * @param countSpec specification used to count results.
 		 * @return
 		 */

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/FetchableFluentQueryByPredicate.java

@@ -31,6 +31,8 @@
 import org.springframework.data.domain.PageImpl;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.ScrollPosition;
+import org.springframework.data.domain.Slice;
+import org.springframework.data.domain.SliceImpl;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.domain.Window;
 import org.springframework.data.jpa.repository.query.KeysetScrollDelegate;
@@ -191,6 +193,11 @@ public Page<R> page(Pageable pageable) {
 		return pageable.isUnpaged() ? new PageImpl<>(all(pageable.getSortOr(this.sort))) : readPage(pageable);
 	}
 
+	@Override
+	public Slice<R> slice(Pageable pageable) {
+		return pageable.isUnpaged() ? new SliceImpl<>(all(pageable.getSortOr(this.sort))) : readSlice(pageable);
+	}
+
 	@Override
 	public Stream<R> stream() {
 
@@ -252,16 +259,40 @@ private void applyQuerySettings(ReturnedType returnedType, int limit, AbstractJP
 	private Page<R> readPage(Pageable pageable) {
 
 		Sort sort = pageable.getSortOr(this.sort);
+		AbstractJPAQuery<?, ?> query = createQuery(pageable, sort);
+
+		List<R> paginatedResults = convert(query.fetch());
+
+		return PageableExecutionUtils.getPage(paginatedResults, withSort(pageable, sort),
+				() -> countOperation.apply(predicate));
+	}
+
+	private Slice<R> readSlice(Pageable pageable) {
+
+		Sort sort = pageable.getSortOr(this.sort);
+		AbstractJPAQuery<?, ?> query = createQuery(pageable, sort);
+		query.limit(pageable.getPageSize() + 1);
+
+		List<?> resultList = query.fetch();
+		boolean hasNext = resultList.size() > pageable.getPageSize();
+		if (hasNext) {
+			resultList = resultList.subList(0, pageable.getPageSize());
+		}
+
+		List<R> slice = convert(resultList);
+
+		return new SliceImpl<>(slice, pageable, hasNext);
+	}
+
+	private AbstractJPAQuery<?, ?> createQuery(Pageable pageable, Sort sort) {
+
 		AbstractJPAQuery<?, ?> query = pagedFinder.apply(sort, pageable);
 
 		if (!properties.isEmpty()) {
 			query.setHint(EntityGraphFactory.HINT, EntityGraphFactory.create(entityManager, entityType, properties));
 		}
 
-		List<R> paginatedResults = convert(query.fetch());
-
-		return PageableExecutionUtils.getPage(paginatedResults, withSort(pageable, sort),
-				() -> countOperation.apply(predicate));
+		return query;
 	}
 
 	private List<R> convert(List<?> resultList) {

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/support/QuerydslJpaPredicateExecutorUnitTests.java

@@ -34,6 +34,7 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
+import org.springframework.data.domain.Slice;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.domain.Sort.Direction;
 import org.springframework.data.domain.Sort.Order;
@@ -399,6 +400,23 @@ void findByFluentPredicatePage() {
 		assertThat(page1.getContent()).containsExactly(oliver);
 	}
 
+	@Test // GH-3764
+	void findByFluentPredicateSlice() {
+
+		Predicate predicate = user.firstname.contains("v");
+
+		Slice<User> slice0 = predicateExecutor.findBy(predicate,
+				q -> q.sortBy(Sort.by("firstname")).slice(PageRequest.of(0, 1)));
+
+		Slice<User> slice1 = predicateExecutor.findBy(predicate,
+				q -> q.sortBy(Sort.by("firstname")).slice(PageRequest.of(1, 1)));
+
+		assertThat(slice0.getContent()).containsExactly(dave);
+		assertThat(slice0.hasNext()).isTrue();
+		assertThat(slice1.getContent()).containsExactly(oliver);
+		assertThat(slice1.hasNext()).isFalse();
+	}
+
 	@Test // GH-3762
 	void findByFluentPredicateSortOverridePage() {
 
@@ -409,7 +427,6 @@ void findByFluentPredicateSortOverridePage() {
 
 		assertThat(page.getContent()).containsOnly(oliver);
 		assertThat(predicateExecutor.findAll(predicate, page.nextPageable())).containsOnly(dave);
-
 	}
 
 	@Test // GH-2294