2 files changed, 42 insertions, 9 deletions

diff --git a/document/src/main/java/com/yahoo/document/DocumentUpdate.java b/document/src/main/java/com/yahoo/document/DocumentUpdate.java
index 2a9ab9e6169..70c5410534e 100644
--- a/document/src/main/java/com/yahoo/document/DocumentUpdate.java
+++ b/document/src/main/java/com/yahoo/document/DocumentUpdate.java
@@ -1,11 +1,14 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.document;
 
+import com.yahoo.document.datatypes.FieldValue;
 import com.yahoo.document.fieldpathupdate.FieldPathUpdate;
 import com.yahoo.document.serialization.DocumentSerializerFactory;
 import com.yahoo.document.serialization.DocumentUpdateReader;
 import com.yahoo.document.serialization.DocumentUpdateWriter;
+import com.yahoo.document.update.AssignValueUpdate;
 import com.yahoo.document.update.FieldUpdate;
+import com.yahoo.document.update.ValueUpdate;
 import com.yahoo.io.GrowableByteBuffer;
 
 import java.util.ArrayList;
@@ -94,6 +97,12 @@ public class DocumentUpdate extends DocumentOperation implements Iterable<FieldP
         docId = id;
     }
 
+    private void verifyType(Document doc) {
+        if (!documentType.equals(doc.getDataType())) {
+            throw new IllegalArgumentException(
+                    "Document " + doc.getId() + " with type " + doc.getDataType() + " must have same type as update, which is type " + documentType);
+        }
+    }
     /**
      * Applies this document update.
      *
@@ -102,10 +111,7 @@ public class DocumentUpdate extends DocumentOperation implements Iterable<FieldP
      * @throws IllegalArgumentException if the document does not have the same document type as this update
      */
     public DocumentUpdate applyTo(Document doc) {
-        if (!documentType.equals(doc.getDataType())) {
-            throw new IllegalArgumentException(
-                    "Document " + doc + " must have same type as update, which is type " + documentType);
-        }
+        verifyType(doc);
 
         for (FieldUpdate fieldUpdate : fieldUpdates) {
             fieldUpdate.applyTo(doc);
@@ -117,6 +123,30 @@ public class DocumentUpdate extends DocumentOperation implements Iterable<FieldP
     }
 
     /**
+     * Prune away any field update that will not modify any field in the document.
+     * @param doc document to check against
+     * @return a reference to itself
+     * @throws IllegalArgumentException if the document does not have the same document type as this update
+     */
+    public DocumentUpdate prune(Document doc) {
+        verifyType(doc);
+
+        for (Iterator<FieldUpdate> iter = fieldUpdates.iterator(); iter.hasNext();) {
+            FieldUpdate update = iter.next();
+            if (!update.isEmpty()) {
+                ValueUpdate last = update.getValueUpdate(update.size() - 1);
+                if (last instanceof AssignValueUpdate) {
+                    FieldValue currentValue = doc.getFieldValue(update.getField());
+                    if ((currentValue != null) && (currentValue.compareTo(last.getValue()) == 0)) {
+                        iter.remove();
+                    }
+                }
+            }
+        }
+        return this;
+    }
+
+    /**
      * Get an unmodifiable list of all field updates that this document update specifies.
      *
      * @return a list of all FieldUpdates in this DocumentUpdate
diff --git a/document/src/main/java/com/yahoo/document/datatypes/Raw.java b/document/src/main/java/com/yahoo/document/datatypes/Raw.java
index 2a5383705df..23ed0cee23e 100644
--- a/document/src/main/java/com/yahoo/document/datatypes/Raw.java
+++ b/document/src/main/java/com/yahoo/document/datatypes/Raw.java
@@ -17,15 +17,16 @@ import java.util.Arrays;
 /**
  * FieldValue which encapsulates a Raw value
  *
- * @author <a href="mailto:einarmr@yahoo-inc.com">Einar M R Rosenvinge</a>
+ * @author Einar M R Rosenvinge
  */
 public final class Raw extends FieldValue {
+
     private static class Factory extends PrimitiveDataType.Factory {
         public FieldValue create() {
             return new Raw();
         }
     }
-    public static PrimitiveDataType.Factory getFactory() { return new Factory(); }
+
     public static final int classId = registerClass(Ids.document + 16, Raw.class);
     private ByteBuffer value;
 
@@ -42,6 +43,8 @@ public final class Raw extends FieldValue {
         value.position(0);
     }
 
+    public static PrimitiveDataType.Factory getFactory() { return new Factory(); }
+
     public ByteBuffer getByteBuffer() {
         return value;
     }
@@ -136,11 +139,11 @@ public final class Raw extends FieldValue {
     }
 
     /* (non-Javadoc)
-      * @see com.yahoo.document.datatypes.FieldValue#deserialize(com.yahoo.document.Field, com.yahoo.document.serialization.FieldReader)
-      */
-
+     * @see com.yahoo.document.datatypes.FieldValue#deserialize(com.yahoo.document.Field, com.yahoo.document.serialization.FieldReader)
+     */
     @Override
     public void deserialize(Field field, FieldReader reader) {
         reader.read(field, this);
     }
+
 }