前言
相信大家在用Java JPA作为ORM的时候都会有这种困惑，就是某个表T我仅仅希望取到其中的A、B、C三个字段，可是jpa是通过Entity Class映射的方式组合查询结果的。
那么如何通过使用JPA查询部分想要的内容，下面我把它做了一些通用的封装，供大家参考。痛快点，直接上代码！
实现
public interface BaseService<T,ID extends Serializable> {List<Object[]> findAllByNavtiveSQLBase(String sql);Page<Object[]> findAllByNavtiveSQLPagingBase(String sql, Pageable pageable);
}
public abstract class BaseServiceImpl<T, ID extends Serializable> implements BaseService<T, ID> { @Autowired
protected BaseRepository<T, ID> baseRepository;
@PersistenceContext(unitName="primaryPersistenceUnit")
@Qualifier(value = "primaryDataSource")
@Autowired
protected EntityManager entityManager;@Override
public List<Object[]> findAllByNavtiveSQLBase(String sql){
try {
Query query = entityManager.createNativeQuery(sql);
@SuppressWarnings("unchecked")
List<Object[]> list = query.getResultList();
System.out.println("list.size() = " + list.size());
entityManager.close();
return list;
} catch (RuntimeException ex) {
throw ex;
}
}@Override
public Page<Object[]> findAllByNavtiveSQLPagingBase(String sql, Pageable pageable){
try {
Query query = entityManager.createNativeQuery(sql);
long total = query.getResultList().size();Iterator<Order> orders = pageable.getSort().iterator();
String pageOrder = orders.hasNext() ? "order by" : "";
while (orders.hasNext()) {
Order order = (Order) orders.next();
pageOrder += String.format(" %s %s%s", order.getProperty(), order.getDirection(), (orders.hasNext() ? ", " : ""));
}int size = pageable.getPageSize();
int begin = (pageable.getPageNumber() - 1) * size;
String pageSql = String.format("%s %s limit %s, %s", sql, pageOrder, begin, size);System.out.println("pageSql = " + pageSql);
query = entityManager.createNativeQuery(pageSql);
@SuppressWarnings("unchecked")
List<Object[]> list = query.getResultList();entityManager.close();
return new PageImpl<Object[]>(list, pageable, total);
} catch (RuntimeException ex) {
throw ex;
}
}
}
@Service
public class ServiceAttendanceRecordImpl extends BaseServiceImpl<AttendanceRecord,Integer> implements ServiceAttendanceRecord {}所有继承了BaseServiceImpl类的实现默认都有了通用的sql查询功能
如何使用
List<Object[]> list = serviceCompanyEntityImpl.findAllByNavtiveSQLBase("SELECT A, B, C FROM T");
for (Object[] objects : list) {
for (Object object : objects) {}
}
