当我在 JDO/DataNucleus 中为聚合函数调用 setResultClass(...) 时，抛出 JDOUserException
使用以下代码
Query query = pm.newQuery(User.class);
query.setFilter( "username == :usernameParam" );
query.setResult( "count(username)" );
query.setResultClass(Long.class);
Object result = query.execute(username);
return (result!=null && (Long)result>0);
我得到这个异常：
javax.jdo.JDOUserException：查询 将返回单个字段，但它是 与 ResultClass (java.lang.Long) ：它是 java.lang.Long
如果我删除 .setResult(Long.class) 查询，它会起作用并返回一个 Long。
也许我不理解 setResult() 方法。我知道我需要设置它来指示我想要什么类型的结果。但 count() 这样的聚合函数不就是这种情况吗？
With the following code
Query query = pm.newQuery(User.class);
query.setFilter( "username == :usernameParam" );
query.setResult( "count(username)" );
query.setResultClass(Long.class);
Object result = query.execute(username);
return (result!=null && (Long)result>0);
I get this exception:
javax.jdo.JDOUserException: The Query
will return a single field but it is
not of a consistent type as the
ResultClass (java.lang.Long) : It is
java.lang.Long
If I remove the .setResult(Long.class) query it works and I get back a Long.
Perhaps I don't understand the setResult() method. I had understood that I need to set this to indicate what type of result I wanted. But is this not the case with aggregate functions such as count()?
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这是几天前修复的。幸运的是，2.1.3 和 2.2 M3 版本已在一小时左右发布；-)
That was fixed several days ago. Fortunately for you versions 2.1.3 and 2.2 M3 were released an hour or so ago ;-)