add toString

Change-Id: I2a38b27164c4c4c0e259a32dbb283dd384b61c26
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/WriteRequest.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/WriteRequest.java
index 1561c2d..99f73c1 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/WriteRequest.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/WriteRequest.java
@@ -4,6 +4,8 @@
 
 import java.util.Objects;
 
+import com.google.common.base.MoreObjects;
+
 /**
  * Database write request.
  */
@@ -67,10 +69,13 @@
 
     @Override
     public String toString() {
-        return "WriteRequest [tableName=" + tableName + ", key=" + key
-                + ", newValue=" + newValue
-                + ", previousVersion=" + previousVersion
-                + ", oldValue=" + oldValue;
+        return MoreObjects.toStringHelper(getClass())
+                .add("tableName", tableName)
+                .add("key", key)
+                .add("newValue", newValue)
+                .add("previousVersion", previousVersion)
+                .add("oldValue", oldValue)
+                .toString();
     }
 
     @Override