Issue #350: Added missing 'hashCode' and 'equals' methods.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch-si.com>

services/thingsearch/persistence/src/main/java/org/eclipse/ditto/services/thingsearch/persistence/write/model/ThingWriteModel.java

@@ -12,6 +12,9 @@
  */
 package org.eclipse.ditto.services.thingsearch.persistence.write.model;
 
+import java.util.Objects;
+
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
 import org.bson.Document;
@@ -60,4 +63,24 @@ private static UpdateOptions upsert() {
         return new UpdateOptions().upsert(true);
     }
 
+    @Override
+    public boolean equals(@Nullable final Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        if (!super.equals(o)) {
+            return false;
+        }
+        final ThingWriteModel that = (ThingWriteModel) o;
+        return thingDocument.equals(that.thingDocument);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(super.hashCode(), thingDocument);
+    }
+
 }