DataNucleus 中 Query.execute() 在什么情况下返回 null
我尚未向数据库添加任何内容，因此根据我的计算，以下查询应返回 0 结果。
Query query = pm.newQuery(Password.class);
query.setFilter("password == :passwordParam");
query.setResult("count(password)");
query.setResultClass(Integer.class);
Integer result = (Integer)query.execute(password);
System.out.println("Result: [" + result + "]");
它返回 null
javadoc 和结果文档都没有说明此方法能够返回 null。我的猜测是我做错了什么。
http://db.apache.org/jdo/api20/apidocs/javax/jdo/Query.html#execute%28%29 http://www.datanucleus.org/products/accessplatform_2_2/jdo/jdoql_result.html
I have not added anything to my Database yet, thus the following query should return a result of 0 by my reckoning.
Query query = pm.newQuery(Password.class);
query.setFilter("password == :passwordParam");
query.setResult("count(password)");
query.setResultClass(Integer.class);
Integer result = (Integer)query.execute(password);
System.out.println("Result: [" + result + "]");
It returns null
Neither the javadocs, nor the result docs, say anything about this method being able to return null. My guess is that I did something wrong.
http://db.apache.org/jdo/api20/apidocs/javax/jdo/Query.html#execute%28%29
http://www.datanucleus.org/products/accessplatform_2_2/jdo/jdoql_result.html
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当我用 DataNucleus 尝试你的代码时，我首先遇到了类似的问题。
字节码增强器未运行。一旦我启用它，计数就变成了预期的 0。
也许你也有类似的问题。
When I tried your code with DataNucleus I experienced a similar problem at first.
The bycode enhancer was not running. Once I enabled it the count became 0 has expected.
Perhaps you're having a similar problem.