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

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

@@ -20,7 +20,6 @@ import static org.springframework.util.ObjectUtils.*;
 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 @@ import com.mongodb.DBObject;
  * @author Christoph Strobl
  * @author Thomas Darimont
  * @author Alexey Plotnik
+ * @author Mark Paluch
  */
 public class Update {
 
@@ -603,6 +603,39 @@ public class Update {
 		}
 	}
 
+	/**
+	 * 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 class Update {
 			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 class UpdateMapperUnitTests {
 		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
 	 */