7
通常我使用NoResultException来返回一个“空”对象,例如,一个空的错误列表或新的BigInteger(“0”),如果我没有得到TypedQuery的结果。现在事实证明,这有时不起作用。突然getSingleResult()返回null,而不是导致NoResultException,我不明白为什么。看看这个例子:JPA:TypedQuery有时返回null而不是NoResultException
public BigInteger pointsSumByAccountId(long accountId)
{
try
{
TypedQuery<BigInteger> pointsQuery = entityManager.createNamedQuery(Points.SumByAccountId, BigInteger.class);
pointsQuery.setParameter(Points.AccountIdParameter, accountId);
return pointsQuery.getSingleResult();
}
catch (NoResultException e)
{
return new BigInteger("0");
}
}
实体的重要组成部分...
@NamedQueries({@NamedQuery(name = "Points.sumByAccountId", query = "select sum(p.value) from Points p where p.validFrom <= current_timestamp() and p.validThru >= current_timestamp() and p.account.id = :accountId")})
public class Points
{
private static final long serialVersionUID = -15545239875670390L;
public static final String SumByAccountId = Points.class.getSimpleName() + ".sumByAccountId";
public static final String AccountIdParameter = "accountId";
.
.
.
如果我使用这将导致没有结果的帐户ID,我得到空的,而不是NoResultException。任何想法为何如此?即使TypedQuery的Javadoc说它必须返回NoResultException:
/**
* Execute a SELECT query that returns a single result.
*
* @return the result
*
* @throws NoResultException if there is no result
* @throws NonUniqueResultException if more than one result
* @throws IllegalStateException if called for a Java
* Persistence query language UPDATE or DELETE statement
* @throws QueryTimeoutException if the query execution exceeds
* the query timeout value set and only the statement is
* rolled back
* @throws TransactionRequiredException if a lock mode has
* been set and there is no transaction
* @throws PessimisticLockException if pessimistic locking
* fails and the transaction is rolled back
* @throws LockTimeoutException if pessimistic locking
* fails and only the statement is rolled back
* @throws PersistenceException if the query execution exceeds
* the query timeout value set and the transaction
* is rolled back
*/
X getSingleResult();
棘手,但解释它,谢谢。 – Bevor 2012-04-24 11:58:38
我知道空集的AVG,MAX和MIN是未定义的,但是空集的SUM是0.我想知道他们为什么会失败。 – VinyJones 2014-07-04 13:46:04
对于非空集,SUM,AVG,MAX或MIN也可以为0。返回null确认空集。 – Ritesh 2014-07-06 03:44:11