DATAMONGO-1457 - Add support for $slice in aggregation.

We now support $slice in aggregation projections via the ProjectionOperationBuilder. Aggregation.project().and("field").slice(10, 20) Original pull request: #372.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2015 the original author or authors.
+ * Copyright 2013-2016 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.
@@ -352,6 +352,7 @@ protected static Object toMongoExpression(AggregationOperationContext context, S
  * 
  * @author Oliver Gierke
  * @author Thomas Darimont
+ * @author Christoph Strobl
  */
 public static class ProjectionOperationBuilder extends AbstractProjectionOperationBuilder {
 
@@ -566,6 +567,31 @@ public ProjectionOperationBuilder size() {
 return project("size");
 }
 
+/**
+ * Generates a {@code $slice} expression that returns a subset of the array held by the given field. <br />
+ * If {@literal n} is positive, $slice returns up to the first n elements in the array. <br />
+ * If {@literal n} is negative, $slice returns up to the last n elements in the array.
+ *
+ * @param count max number of elements.
+ * @return never {@literal null}.
+ * @since 1.10
+ */
+public ProjectionOperationBuilder slice(int count) {
+return project("slice", count);
+}
+
+/**
+ * Generates a {@code $slice} expression that returns a subset of the array held by the given field. <br />
+ *
+ * @param count max number of elements. Must not be negative.
+ * @param offset the offset within the array to start from.
+ * @return never {@literal null}.
+ * @since 1.10
+ */
+public ProjectionOperationBuilder slice(int count, int offset) {
+return project("slice", offset, count);
+}
+
 /* 
  * (non-Javadoc)
  * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDBObject(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java

@@ -1228,6 +1228,27 @@ public void outShouldOutBeTheLastOperation() {
 skip(100));
 }
 
+/**
+ * @see DATAMONGO-1457
+ */
+@Test
+public void sliceShouldBeAppliedCorrectly() {
+
+assumeTrue(mongoVersion.isGreaterThanOrEqualTo(THREE_DOT_TWO));
+
+createUserWithLikesDocuments();
+
+TypedAggregation<UserWithLikes> agg = newAggregation(UserWithLikes.class, match(new Criteria()),
+project().and("likes").slice(2));
+
+AggregationResults<UserWithLikes> result = mongoTemplate.aggregate(agg, UserWithLikes.class);
+
+assertThat(result.getMappedResults(), hasSize(9));
+for (UserWithLikes user : result) {
+assertThat(user.likes.size() <= 2, is(true));
+}
+}
+
 private void createUsersWithReferencedPersons() {
 
 mongoTemplate.dropCollection(User.class);

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2015 the original author or authors.
+ * Copyright 2013-2016 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.
@@ -36,6 +36,7 @@
  * 
  * @author Oliver Gierke
  * @author Thomas Darimont
+ * @author Christoph Strobl
  */
 public class ProjectionOperationUnitTests {
 
@@ -371,6 +372,36 @@ public void shouldRenderGenericSizeExpressionInProjection() {
 assertThat(projected.get("tags_count"), is((Object) new BasicDBObject("$size", Arrays.asList("$tags"))));
 }
 
+/**
+ * @see DATAMONGO-1457
+ */
+@Test
+public void shouldRenderSliceCorrectly() throws Exception {
+
+ProjectionOperation operation = Aggregation.project().and("field").slice(10).as("renamed");
+
+DBObject dbObject = operation.toDBObject(Aggregation.DEFAULT_CONTEXT);
+DBObject projected = exctractOperation("$project", dbObject);
+
+assertThat(projected.get("renamed"),
+is((Object) new BasicDBObject("$slice", Arrays.<Object> asList("$field", 10))));
+}
+
+/**
+ * @see DATAMONGO-1457
+ */
+@Test
+public void shouldRenderSliceWithPositionCorrectly() throws Exception {
+
+ProjectionOperation operation = Aggregation.project().and("field").slice(10, 5).as("renamed");
+
+DBObject dbObject = operation.toDBObject(Aggregation.DEFAULT_CONTEXT);
+DBObject projected = exctractOperation("$project", dbObject);
+
+assertThat(projected.get("renamed"),
+is((Object) new BasicDBObject("$slice", Arrays.<Object> asList("$field", 5, 10))));
+}
+
 private static DBObject exctractOperation(String field, DBObject fromProjectClause) {
 return (DBObject) fromProjectClause.get(field);
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/UserWithLikes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2016 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.
@@ -20,16 +20,23 @@
 import java.util.HashSet;
 import java.util.Set;
 
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
 /**
  * @author Thomas Darimont
+ * @author Christoph Strobl
  */
+@Data
+@NoArgsConstructor
 public class UserWithLikes {
 
 String id;
 Date joined;
 Set<String> likes = new HashSet<String>();
 
 public UserWithLikes(String id, Date joined, String... likes) {
+
 this.id = id;
 this.joined = joined;
 this.likes = new HashSet<String>(Arrays.asList(likes));