Google数据存储 - 查询关键值 [英] Google datastore - querying on key values

问题描述

我有一个EntityKind SuggestedInterest。
当我用一个关键字GrpId和属性suggestedint来填充它。

现在，我需要为请求的GrpId

因此，我将查询写为：

 字符串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）; 
实体结果= pq0.asSingleEntity（）; 
返回result.getProperty（suggestedint）。toString（）; 
} 
  

当我执行这段代码时，我得到了

  java.lang.IllegalArgumentException：__key__过滤器值必须是键
  

开发者文档告诉使用Entity.KEY_RESERVED_PROPERTY来查询密钥，但我想我误解了。什么是正确的方式来查询关键？

解决方案

您应该传递一个键而不是字符串：

 密钥grpKey = KeyFactory。然后使用它： 
 
 
  Filter filter = 
 FilterPredicate（Entity.KEY_RESERVED_PROPERTY，FilterOperator.EQUAL，grpKey）; 
  
 
I have a EntityKind SuggestedInterest. 
When I populate that with a key "GrpId" and property "suggestedint".

Now, I need the "suggestedint" value for a requested "GrpId"

So, I write the query as:
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();       
}
When I execute this code I get 
java.lang.IllegalArgumentException: __key__ filter value must be a Key
The developer docs told to use Entity.KEY_RESERVED_PROPERTY to query on keys, but I guess I misunderstood. What is the correct way to query on key ?
解决方案
You should pass it a Key instead of String:
Key grpKey = KeyFactory.createKey("SuggestedInterest", grpId)
then use it:
 Filter filter = 
    new FilterPredicate(Entity.KEY_RESERVED_PROPERTY,FilterOperator.EQUAL,grpKey);


                        
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