Google数据存储区 - 查询关键值

Question

我有一个EntityKind SuggestedInterest.当我使用键"GrpId"和属性"suggestedint"填充它时.

现在,我需要"suggestint"值来请求"GrpId"

所以,我把查询写成:

String findSuggestedInterest(String grpId)
{
    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
    Filter filter = new FilterPredicate(Entity.KEY_RESERVED_PROPERTY,FilterOperator.EQUAL,grpId);
    Query q0 = new Query("SuggestedInterest").setFilter(filter);
    PreparedQuery pq0 = datastore.prepare(q0);
    Entity result = pq0.asSingleEntity();
    return result.getProperty("suggestedint").toString();       
}

当我执行此代码时,我得到了

java.lang.IllegalArgumentException: __key__ filter value must be a Key

开发人员讲述了使用Entity.KEY_RESERVED_PROPERTY来查询密钥,但我想我误解了.查询密钥的正确方法是什么？

Answer 1

你应该传递它Key而不是String:

Key grpKey = KeyFactory.createKey("SuggestedInterest", grpId)

然后使用它:

 Filter filter = 
    new FilterPredicate(Entity.KEY_RESERVED_PROPERTY,FilterOperator.EQUAL,grpKey);