Spring Data Jpa多表查询返回自定义实体

比如来看一下这样的一条SQL语句,这是一个三张表的多表查询,显然在JPA中用一个实体类是接受不了这些参数的

select 
t1.id as chapterId ,
t1.name as chapterName ,
t2.id as unitId,
t2.name as unitName ,
t3.id as lessonId,
t3.name as lessonName
from  t_chapter t1
LEFT JOIN  t_unit t2 on t1.id =t2.chapter_id
LEFT JOIN t_lession t3 on t3.unit_id =t2.id 
where t1.id= '4028b4816305ea91016305eec24f0000' 
and t2.id='4028b4816305f1a6016305f423180000'
and t3.id= '4028b4816306007b016306020bb80000';

Repository

/**
 * Created by ZhuPengWei on 2018/5/11.
 */
public interface TestRepository extends JpaRepository<ProductInfo, String > {


    @Query(
            value = "select \n" +
                    "t1.id as chapterId ,t1.name as chapterName ,t2.id as unitId,t2.name as unitName ,t3.id as lessonId,t3.name as lessonName\n" +
                    "from  t_chapter t1\n" +
                    "LEFT JOIN  t_unit t2 on t1.id =t2.chapter_id\n" +
                    "LEFT JOIN t_lession t3 on t3.unit_id =t2.id \n" +
                    "where t1.id= :chapterId \n" +
                    "and t2.id=:unitId \n" +
                    "and t3.id= :lessonId",
            nativeQuery = true
    )
    List<Object[]> select(@Param("chapterId") String chapterId, @Param("unitId") String unitId, @Param("lessonId") String lessonId);

}

好下面到单元测试

/**
 * Created by ZhuPengWei on 2018/5/11.
 */
@RunWith(SpringRunner.class)
@SpringBootTest
public class TestRepositoryTest {

    @Autowired
    private TestRepository testRepository;

    @Test
    public void select() throws Exception {
        List<Object[]> select = testRepository.select("4028b4816305ea91016305eec24f0000", "4028b4816305f1a6016305f423180000", "4028b4816306007b016306020bb80000");

        List<TestView> testViews = castEntity(select, TestView.class);

        Assert.assertTrue(testViews.size() > 0);
    }


    //转换实体类
    public static <T> List<T> castEntity(List<Object[]> list, Class<T> clazz) throws Exception {
        List<T> returnList = new ArrayList<T>();
        Object[] co = list.get(0);
        Class[] c2 = new Class[co.length];

        //确定构造方法
        for (int i = 0; i < co.length; i++) {
            c2[i] = co[i].getClass();
        }

        for (Object[] o : list) {
            Constructor<T> constructor = clazz.getConstructor(c2);
            returnList.add(constructor.newInstance(o));
        }

        return returnList;
    }
}

自定义实体

/**
 * Created by ZhuPengWei on 2018/5/11.
 */
@Data
public class TestView {


    private String chapterId;
    private String chapterName;
    private String unitId;
    private String unitName;
    private String lessonId;
    private String lessonName;

    public TestView() {
    }

    public TestView(String chapterId, String chapterName, String unitId, String unitName, String lessonId, String lessonName) {
        this.chapterId = chapterId;
        this.chapterName = chapterName;
        this.unitId = unitId;
        this.unitName = unitName;
        this.lessonId = lessonId;
        this.lessonName = lessonName;
    }
}

需要注意的是 SQL语句的字段顺序一定要与实体类字段的顺序保持一致,否则会出现参数封装错误的情况