findDistinctByFirstNameIgnoreCaseAndLastNameOrderByAgeDesc(String firstName,String lastName)

@PersistenceContext
private EntityManager em;  // 注入实体管理器
@SuppressWarnings("unchecked")
public Page<Student> search(User user) {
    String dataSql = "select t from User t where 1 = 1";
    String countSql = "select count(t) from User t where 1 = 1";
    
    if(null != user && !StringUtils.isEmpty(user.getName())) {
        dataSql += " and t.name = ?1";
        countSql += " and t.name = ?1";
    }
    
    Query dataQuery = em.createQuery(dataSql);
    Query countQuery = em.createQuery(countSql);
    
    if(null != user && !StringUtils.isEmpty(user.getName())) {
        dataQuery.setParameter(1, user.getName());
        countQuery.setParameter(1, user.getName());
    }long totalSize = (long) countQuery.getSingleResult();
    Page<User> page = new Page();
    page.setTotalSize(totalSize);
    List<User> data = dataQuery.getResultList();
    page.setData(data);
    return page;
}

public void updateBatch(List<Z> list) {
		for (int i = 0; i < list.size(); i++) {
			entityManager.merge(list.get(i)); // 变成托管状态
			if (i % 30 == 0) {
				entityManager.flush(); // 变成持久化状态
				entityManager.clear(); // 变成游离状态
			}
		}
	}
 
	public void saveBatch(List<Z> list) {
		for (int i = 0; i < list.size(); i++) {
			entityManager.persist(list.get(i)); // 变成托管状态
			if (i % 30 == 0) {
				entityManager.flush(); // 变成持久化状态
				entityManager.clear(); // 变成游离状态
			}
		}
	}

@PersistenceContext
private EntityManager em;  // 注入实体管理器
@SuppressWarnings("unchecked")
public Page<Student> search(User user) {
    String dataSql = "select t from User t where 1 = 1";
    String countSql = "select count(t) from User t where 1 = 1";
    
    if(null != user && !StringUtils.isEmpty(user.getName())) {
        dataSql += " and t.name = ?1";
        countSql += " and t.name = ?1";
    }
    
    Query dataQuery = em.createQuery(dataSql);
    Query countQuery = em.createQuery(countSql);
    
    if(null != user && !StringUtils.isEmpty(user.getName())) {
        dataQuery.setParameter(1, user.getName());
        countQuery.setParameter(1, user.getName());
    }
    long totalSize = (long) countQuery.getSingleResult();
    Page<User> page = new Page();
    page.setTotalSize(totalSize);
    List<User> data = dataQuery.getResultList();
    page.setData(data);
    return page;
}

CriteriaBuilder cb = entityManager.getCriteriaBuilder ();  // criteriaQuery工厂
CriteriaQuery cq = cb.createQuery(); //查询语句构造器
Root<User> root = cq.from(User.class);  //获取查询根对象
cq.select(root);   // select u from User u
Predicate pre = cb.greaterThan(root.get("age").as(Integer.class), 20); // age大于20
cq.where(pre); // select u from User u where u.age > 20
// 上面这一串的目的就是为了构造出    select u from User u where u.age > 20  的JPQL语句
Query query = em.createQuery(cq);
List<User> users = query.getResultList();

Predicate pre = cb.greaterThan(root.get("age").as(Integer.class), 20); // age大于20
Predicate pre2 = cb.lessThan(root.get("age").as(Integer.class), 40); // age小于40
cq.where(pre)改成cq.where(pre,pre2);

public interface UserRepository extends JpaRepository<User, Integer> , JapSpecificationExecutor<User>{
 
}

public List<User> getUsers(){
    return userRepository.findAll(new Specification<User>(){
        @Override
        public Predicate toPredicate(Root<User>, CriteriaQuery<?> cq, CriteriaBuilder cb){
            List<Predicate> preList = new ArrayList();
            // 跟上面Criteria的条件构造是一样的
            // ..........
            // ..........
            // 条件构造完毕，都在 preList 里面
            return cq.where(preList.toArray(new Predicate[preList.size()])).getRestriction();
        }            
    }) ;       
}

@Query(value="select  u from user u where name like ?1"， nativeQuery = true)

@RunWith(SpringRunner.class)
@SpringBootTest
class JpaProjectApplicationTests {
    @Autowired
    private EntityManager entityManager;
    //查询工厂实体
    private JPAQueryFactory queryFactory;

    @PostConstruct
    public void initFactory() {
        queryFactory = new JPAQueryFactory(entityManager);
    }
    @Test
    void contextLoads() {
        User user = new User("ws","123");
        QUser qUser = QUser.user;
        // 定于获取条件
        BooleanBuilder booleanBuilder = new BooleanBuilder();
        // 要查询的条件
        if(!StringUtils.isEmpty(user.getUsername())){
            // 放入要查询的条件信息
            booleanBuilder.and(qUser.username.contains(user.getUsername()));
        }
        // 要查询的条件
        if(!StringUtils.isEmpty(user.getPassword())){
            booleanBuilder.and(qUser.password.contains(user.getPassword()));
        }
        List<User> fetch = queryFactory.select(qUser).from(qUser).where(booleanBuilder).orderBy(qUser.creatTime.desc()).fetch();
        for (User fetch1 : fetch) {
            System.out.println(fetch1.getId()+"+++++++++++++++++++++");
        }
    }
}

@RunWith(SpringRunner.class)
@SpringBootTest
class JpaProjectApplicationTests {
    @Autowired
    private EntityManager entityManager;
    //查询工厂实体
    private JPAQueryFactory queryFactory;

    private int roleId = 1;
    private int userId = 1;

    @PostConstruct
    public void initFactory() {
        queryFactory = new JPAQueryFactory(entityManager);
    }

    @Test
    void contextLoads() {
        QUser qUser = QUser.user;
        QRole qRole = QRole.role;
        QUserRole qUserRole = QUserRole.userRole;

        // 定于获取条件
        BooleanBuilder booleanBuilder = new BooleanBuilder();
        // 要查询的条件
        if (!StringUtils.isEmpty(roleId)) {
            // 放入要查询的条件信息
            booleanBuilder.and(qUserRole.roleId.eq(roleId));
        }
        // 要查询的条件
        if (!StringUtils.isEmpty(userId)) {
            // 放入要查询的条件信息
            booleanBuilder.and(qUserRole.userId.eq(userId));
        }
        
        QueryResults<UserRoleVo> queryResults = queryFactory.select(Projections.bean(UserRoleVo.class, qUser.username, qRole.roleName)).from(qUser, qUserRole, qRole).where(booleanBuilder).fetchResults();
        queryResults.getResults().stream().forEach(r ->{
            System.out.println(r.getUsername() + "++++++++++++"+r.getRoleName());
        });

    }
}