DATAMONGO-832 - Add support for $slice in Update.push.

We now support $slice in Update operations via the PushOperatorBuilder. new Update().push("key").slice(5).each(Arrays.asList("one", "two", "three")); Original Pull Request: #374

Author: mp911de

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/Update.java

@@ -20,7 +20,6 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.Date;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -44,6 +43,7 @@
  * @author Christoph Strobl
  * @author Thomas Darimont
  * @author Alexey Plotnik
+ * @author Mark Paluch
  */
 public class Update {
 
@@ -603,6 +603,39 @@ public boolean equals(Object that) {
 }
 }
 
+/**
+ * Implementation of {@link Modifier} representing {@code $slice}.
+ *
+ * @author Mark Paluch
+ * @since 1.10
+ */
+private static class Slice implements Modifier {
+
+private int count;
+
+public Slice(int count) {
+this.count = count;
+}
+
+/*
+ * (non-Javadoc)
+ * @see org.springframework.data.mongodb.core.query.Update.Modifier#getKey()
+ */
+@Override
+public String getKey() {
+return "$slice";
+}
+
+/*
+ * (non-Javadoc)
+ * @see org.springframework.data.mongodb.core.query.Update.Modifier#getValue()
+ */
+@Override
+public Object getValue() {
+return this.count;
+}
+}
+
 /**
  * {@link Modifier} implementation used to propagate {@code $position}.
  *
@@ -656,6 +689,23 @@ public Update each(Object... values) {
 return Update.this.push(key, this.modifiers);
 }
 
+/**
+ * Propagates {@code $slice} to {@code $push}. {@code $slice} requires the {@code $each operator}. <br />
+ * If {@literal count} is zero, {@code $slice} updates the array to an empty array. <br />
+ * If {@literal count} is negative, {@code $slice} updates the array to contain only the last {@code count}
+ * elements. <br />
+ * If {@literal count} is positive, {@code $slice} updates the array to contain only the first {@code count}
+ * elements. <br />
+ *
+ * @param count
+ * @return
+ */
+public PushOperatorBuilder slice(int count) {
+
+this.modifiers.addModifier(new Slice(count));
+return this;
+}
+
 /**
  * Forces values to be added at the given {@literal position}.
  *

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/UpdateMapperUnitTests.java

@@ -373,6 +373,24 @@ public void updatePushEachAtPositionWorksCorrectlyWhenGivenPositionNull() {
 assertThat(getAsDBObject(push, "key").containsField("$each"), is(true));
 }
 
+/**
+ * @see DATAMONGO-832
+ */
+@Test
+public void updatePushEachWithSliceShouldRenderCorrectly() {
+
+Update update = new Update().push("key").slice(5).each(Arrays.asList("Arya", "Arry", "Weasel"));
+
+DBObject mappedObject = mapper.getMappedObject(update.getUpdateObject(), context.getPersistentEntity(Object.class));
+
+DBObject push = getAsDBObject(mappedObject, "$push");
+DBObject key = getAsDBObject(push, "key");
+
+assertThat(key.containsField("$slice"), is(true));
+assertThat((Integer) key.get("$slice"), is(5));
+assertThat(getAsDBObject(push, "key").containsField("$each"), is(true));
+}
+
 /**
  * @see DATAMONGO-410
  */