Appengine實體更新不起作用

我正在開發應用程序引擎的代碼。我試圖通過更新查詢結果返回的相同實體來更新現有行。但它會創建新的行而不是更新同一行。以下是代碼：Appengine實體更新不起作用

public boolean updateProfile(DbProfile profile) { 

Transaction txn = _datastore.beginTransaction(); 
Entity entity = getProfileEntity(profile.getLoginId()); 
if (entity != null) { 
    entity.setProperty(DbProfile.DbProfilePropertyNames.address, profile.getAddress()); 
    entity.setProperty(DbProfile.DbProfilePropertyNames.name, profile.getName()); 
    Key key = _datastore.put(entity); 
    txn.commit(); 
    return true; 
} 
return false; 
} 

private Entity getProfileEntity(String userName) { 

Key eRecommendationKey = KeyFactory.createKey("eRecommendation", _dbKeyName); 
FilterPredicate predicateUsername = 
    new FilterPredicate(DbProfile.DbProfilePropertyNames.loginId, FilterOperator.EQUAL, 
       userName.toUpperCase()); 
Query query = 
    new Query(DbProfile.entityProfileName, eRecommendationKey).setFilter(predicateUsername); 
List<Entity> profiles = 
     _datastore.prepare(query).asList(FetchOptions.Builder.withDefaults()); 
Utils.log.log(Level.SEVERE, "not found"+profiles.size()); 
if (profiles.size() == 0) { 
    //profile data is not set yet 
    return null; 
} else { 
    return profiles.get(0); 
} 
}

下圖顯示了實體中的字段。