Implement toString()

- add more debug logs

Change-Id: I1541d66f24d2dde0712a4daef081ca1f49951ef8
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
index 3594adb..dfeb4c1 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DefaultTransactionalMap.java
@@ -30,6 +30,7 @@
 
 import static com.google.common.base.Preconditions.*;
 
+import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
 import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheLoader;
@@ -193,6 +194,15 @@
         return updates;
     }
 
+    // TODO: build expected result Map processing DB updates?
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+                .add("backingMap", backingMap)
+                .add("updates", prepareDatabaseUpdates())
+                .toString();
+    }
+
     /**
      * Discards all changes made to this transactional map.
      */