Polishing.

Move SliceUtils to another package for reuse. Slightly alter its API, add tests and update javadoc.

Original Pull Request: #4890

Author: christophstrobl

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/MongoQueryExecution.java

@@ -36,6 +36,7 @@
 import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.UpdateDefinition;
+import org.springframework.data.mongodb.repository.util.SliceUtils;
 import org.springframework.data.support.PageableExecutionUtils;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
@@ -87,7 +88,7 @@ public Object execute(Query query) {
 			int pageSize = pageable.getPageSize();
 
 			// Apply Pageable but tweak limit to peek into next page
-			Query modifiedQuery = query.with(pageable).limit(pageSize + 1);
+			Query modifiedQuery = SliceUtils.limitResult(query, pageable).with(pageable.getSort());
 			List result = find.matching(modifiedQuery).all();
 
 			boolean hasNext = result.size() > pageSize;

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/ReactiveSpringDataMongodbQuery.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.mongodb.repository.support;
 
+import org.springframework.data.mongodb.repository.util.SliceUtils;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -113,14 +114,16 @@ Mono<Page<K>> fetchPage(Pageable pageable) {
 	/**
 	 * Fetch all matching query results as Slice.
 	 *
+	 * @param pageable defines range and sort of requested slice
 	 * @return {@link Mono} emitting the requested Slice.
+	 * @since 4.5
 	 */
 	Mono<Slice<K>> fetchSlice(Pageable pageable) {
 
-		Mono<List<K>> content = createQuery().map(it -> SliceUtils.getQuery(it, pageable))
+		Mono<List<K>> content = createQuery().map(it -> SliceUtils.limitResult(it, pageable).with(pageable.getSort()))
 				.flatMapMany(it -> find.matching(it).all()).collectList();
 
-		return content.map(it -> SliceUtils.getSlice(it, pageable));
+		return content.map(it -> SliceUtils.sliceResult(it, pageable));
 	}
 
 	/**

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SimpleMongoRepository.java

@@ -43,6 +43,7 @@
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.repository.MongoRepository;
 import org.springframework.data.mongodb.repository.query.MongoEntityInformation;
+import org.springframework.data.mongodb.repository.util.SliceUtils;
 import org.springframework.data.support.PageableExecutionUtils;
 import org.springframework.data.util.StreamUtils;
 import org.springframework.data.util.Streamable;
@@ -460,9 +461,9 @@ public Slice<T> slice(Pageable pageable) {
 
 			Assert.notNull(pageable, "Pageable must not be null");
 
-			List<T> resultList = createQuery(q -> SliceUtils.getQuery(q, pageable)).all();
+			List<T> resultList = createQuery(q -> SliceUtils.limitResult(q, pageable).with(pageable.getSort())).all();
 
-			return SliceUtils.getSlice(resultList, pageable);
+			return SliceUtils.sliceResult(resultList, pageable);
 		}
 
 		@Override

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SimpleReactiveMongoRepository.java

@@ -17,6 +17,7 @@
 
 import static org.springframework.data.mongodb.core.query.Criteria.*;
 
+import org.springframework.data.mongodb.repository.util.SliceUtils;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -596,8 +597,8 @@ public Mono<Page<T>> page(Pageable pageable) {
 		@Override
 		public Mono<Slice<T>> slice(Pageable pageable) {
 
-			return createQuery(q -> SliceUtils.getQuery(q, pageable)).all().collectList()
-					.map(it -> SliceUtils.getSlice(it, pageable));
+			return createQuery(q -> SliceUtils.limitResult(q, pageable).with(pageable.getSort())).all().collectList()
+					.map(it -> SliceUtils.sliceResult(it, pageable));
 		}
 
 		@Override

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SpringDataMongodbQuery.java

@@ -34,6 +34,7 @@
 import org.springframework.data.mongodb.core.mapping.FieldName;
 import org.springframework.data.mongodb.core.query.BasicQuery;
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.mongodb.repository.util.SliceUtils;
 import org.springframework.data.support.PageableExecutionUtils;
 import org.springframework.lang.Nullable;
 
@@ -187,14 +188,15 @@ public Page<T> fetchPage(Pageable pageable) {
 	/**
 	 * Fetch a {@link Slice}.
 	 *
-	 * @param pageable
-	 * @return
+	 * @param pageable defines range and sort of requested slice
+	 * @return new instance of {@link Slice} containing matching results within range.
+	 * @since 4.5
 	 */
 	public Slice<T> fetchSlice(Pageable pageable) {
 
-		List<T> content = find.matching(SliceUtils.getQuery(createQuery(), pageable)).all();
+		List<T> content = find.matching(SliceUtils.limitResult(createQuery(), pageable).with(pageable.getSort())).all();
 
-		return SliceUtils.getSlice(content, pageable);
+		return SliceUtils.sliceResult(content, pageable);
 	}
 
 	@Override

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SliceUtils.java renamed to spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/util/SliceUtils.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.data.mongodb.repository.support;
+package org.springframework.data.mongodb.repository.util;
 
 import java.util.List;
 
@@ -26,19 +26,21 @@
  * Utility methods for {@link Slice} handling.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  * @since 4.5
  */
-class SliceUtils {
+public class SliceUtils {
 
 	/**
 	 * Creates a {@link Slice} given {@link Pageable} and {@link List} of results.
 	 *
-	 * @param <T>
-	 * @param resultList
-	 * @param pageable
-	 * @return
+	 * @param <T> the element type.
+	 * @param resultList the source list holding the result of the request. If the result list contains more elements
+	 *          (indicating a next slice is available) it is trimmed to the {@link Pageable#getPageSize() page size}.
+	 * @param pageable the source pageable.
+	 * @return new instance of {@link Slice}.
 	 */
-	public static <T> Slice<T> getSlice(List<T> resultList, Pageable pageable) {
+	public static <T> Slice<T> sliceResult(List<T> resultList, Pageable pageable) {
 
 		boolean hasNext = resultList.size() > pageable.getPageSize();
 
@@ -50,16 +52,23 @@ public static <T> Slice<T> getSlice(List<T> resultList, Pageable pageable) {
 	}
 
 	/**
-	 * Customize query for slice retrieval.
+	 * Customize query for {@link #sliceResult sliced result} retrieval. If {@link Pageable#isPaged() paged} the
+	 * {@link Query#limit(int) limit} is set to {@code pagesize + 1} in order to determine if more data is available.
 	 *
-	 * @param query
-	 * @param pageable
-	 * @return
+	 * @param query the source query
+	 * @param pageable paging to apply.
+	 * @return new instance of {@link Query} if either {@link Pageable#isPaged() paged}, the source query otherwise.
 	 */
-	public static Query getQuery(Query query, Pageable pageable) {
+	public static Query limitResult(Query query, Pageable pageable) {
 
-		query.with(pageable);
+		if (pageable.isUnpaged()) {
+			return query;
+		}
+
+		Query target = Query.of(query);
+		target.skip(pageable.getOffset());
+		target.limit(pageable.getPageSize() + 1);
 
-		return pageable.isPaged() ? query.limit(pageable.getPageSize() + 1) : query;
+		return target;
 	}
 }

Diff for: spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/util/SliceUtilsUnitTests.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.repository.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verifyNoInteractions;
+
+import java.util.stream.Stream;
+
+import org.bson.Document;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.domain.Sort;
+import org.springframework.data.domain.Sort.Direction;
+import org.springframework.data.mongodb.core.query.BasicQuery;
+import org.springframework.data.mongodb.core.query.Query;
+
+/**
+ * Unit test for {@link SliceUtils}.
+ *
+ * @author Christoph Strobl
+ */
+class SliceUtilsUnitTests {
+
+	@ParameterizedTest // GH-4889
+	@MethodSource("paged")
+	void pagedPageableModifiesQuery(Pageable page) {
+
+		Query source = new BasicQuery(Document.parse("{ 'spring' : 'data' }"));
+
+		Query target = SliceUtils.limitResult(source, page);
+
+		assertThat(target.getQueryObject()).isEqualTo(source.getQueryObject());
+		assertThat(target).isNotSameAs(source);
+		assertThat(target.isLimited()).isTrue();
+		assertThat(target.getSkip()).isEqualTo(page.getOffset());
+		assertThat(target.getLimit()).isEqualTo(page.toLimit().max() + 1);
+		assertThat(target.getSortObject()).isEqualTo(source.getSortObject());
+	}
+
+	@ParameterizedTest // GH-4889
+	@MethodSource("unpaged")
+	void unpagedPageableDoesNotModifyQuery(Pageable page) {
+
+		Query source = spy(new BasicQuery(Document.parse("{ 'spring' : 'data' }")));
+
+		Query target = SliceUtils.limitResult(source, page);
+
+		verifyNoInteractions(source);
+
+		assertThat(target).isSameAs(source);
+		assertThat(target.isLimited()).isFalse();
+	}
+
+	public static Stream<Arguments> paged() {
+		return Stream.of(Arguments.of(Pageable.ofSize(1)), Arguments.of(PageRequest.of(0, 10)),
+				Arguments.of(PageRequest.of(0, 10, Direction.ASC, "name")));
+	}
+
+	public static Stream<Arguments> unpaged() {
+		return Stream.of(Arguments.of(Pageable.unpaged()), Arguments.of(Pageable.unpaged(Sort.by("name"))));
+	}
+}