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
    
       {        List
     
       findAllByNavtiveSQLBase(String sql);        Page
      
        findAllByNavtiveSQLPagingBase(String sql, Pageable pageable);}
      
     
    

public abstract class BaseServiceImpl
    
      implements BaseService
     
         {    @Autowired    protected BaseRepository
      
        baseRepository;    @PersistenceContext(unitName="primaryPersistenceUnit")    @Qualifier(value = "primaryDataSource")    @Autowired    protected EntityManager entityManager;    @Override    public List
       
         findAllByNavtiveSQLBase(String sql){        try {            Query query = entityManager.createNativeQuery(sql);            @SuppressWarnings("unchecked")            List
        
          list = query.getResultList();            System.out.println("list.size() = " + list.size());            entityManager.close();            return list;        } catch (RuntimeException ex) {            throw ex;        }    }        @Override    public Page
         
           findAllByNavtiveSQLPagingBase(String sql, Pageable pageable){ try { Query query = entityManager.createNativeQuery(sql); long total = query.getResultList().size(); Iterator
          
            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
           
             list = query.getResultList(); entityManager.close(); return new PageImpl
            
             (list, pageable, total); } catch (RuntimeException ex) { throw ex; } }}
            
           
          
         
        
       
      
     
    

@Servicepublic class ServiceAttendanceRecordImpl extends BaseServiceImpl
    
      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
    
      list = serviceCompanyEntityImpl.findAllByNavtiveSQLBase("SELECT A, B, C FROM T");        for (Object[] objects : list) {            for (Object object : objects) {            }        }