我正在使用 JPA 2.1(Eclipselink 供应商)@SqlResultSetMapping 将 sql 查询映射到无实体 POJO，当 sql 结果不为空时它有效，但当我的表为空时 
我的 POJO 的构造失败，但出现异常:
2016-05-30 11:44:17,154 [tp520017379-230] ERROR - Exception [EclipseLink-6177] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.QueryException
Exception Description: The column result [st_agg] was not found in the results of the query.
Query: ResultSetMappingQuery(name="nodeStatusAggQuery" sql="select max(status) as st_agg, max(clock_accuracy_health) as cac_agg, max(clock_analysis_health) as can_agg, max(ptp_net_analysis_health) as na_agg from sync_node where ncd_id = ? and type =?")
javax.persistence.PersistenceException: Exception [EclipseLink-6177] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.QueryException
Exception Description: The column result [st_agg] was not found in the results of the query.
我期望空结果应该由 JPA 自动处理，例如通过调用我的 POJO 的默认构造函数。我找到了一种通过捕获异常来解决问题的解决方法，但是我的问题我可以让 JPA 自动处理空结果吗？或任何其他建议？
Code Sample:
public static SyncNodeStatusAggregation getMaxSeverStatusAndHealth(int ncdId, SyncProtocolType type){
try {
EntityManager em = ...
Query aggregateQuery = em.createNamedQuery(SyncNodeDBImpl.NODE_STATUS_AGG_QUERY);
aggregateQuery.setParameter(1, ncdId);
aggregateQuery.setParameter(2, type.ordinal());
return (SyncNodeStatusAggregation) aggregateQuery.getSingleResult();
//javax.persistence.PersistenceException can be thrown when result is empty, JPA will not be able to map the result to object, thus we handle it be catching the exception
} catch (PersistenceException e) {
return new SyncNodeStatusAggregation(SyncNodeStatus.Ok, SyncHealthIndication.na, SyncHealthIndication.na, SyncHealthIndication.na );
}
}
@SqlResultSetMapping(
name = SyncNodeDBImpl.RESULT_MAPPING_NAME,
classes = {
@ConstructorResult(
targetClass = SyncNodeStatusAggregation.class,
columns = {
@ColumnResult(name = "st_agg"),
@ColumnResult(name = "cac_agg"),
@ColumnResult(name = "can_agg"),
@ColumnResult(name = "na_agg"),
}
)
}
)
@NamedNativeQuery(
name = SyncNodeDBImpl.NODE_STATUS_AGG_QUERY,
query = "select max(status) as st_agg, max(clock_accuracy_health) as cac_agg, max(clock_analysis_health) as can_agg, max(ptp_net_analysis_health) as na_agg from sync_node where ncd_id = ?1 and type =?2",
resultSetMapping =SyncNodeDBImpl.RESULT_MAPPING_NAME
)
最佳答案
你需要像这样指定类型:
@ColumnResult(name = "na_agg",type="Double.class")
关于java - JPA @SqlResultSetMapping 无法处理要映射到空 POJO 的空 sql 结果 - 而是抛出异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37524544/