SpringData专题(六)-JPA中的复杂查询

JPQL全称Java Persistence Query Language
基于首次在EJB2.0中引入的EJB查询语言(EJB QL),Java持久化查询语言(JPQL)是一种可移植的查询语言，旨在以面向对象表达式语言的表达式，将SQL语法和简单查询语义绑定在一起·使用这种语言编写的查询是可移植的，可以被编译成所有主流数据库服务器上的SQL。
其特征与原生SQL语句类似，并且完全面向对象，通过类名和属性访问，而不是表名和表的属性。

Hibernate框架查询语言: HQL

JPA查询语言: JPQL

1.抽取JPAUtil工具类

/**
 * @author bruceliu
 * @create 2019-07-30 14:10
 * @description JPA的工具类(事务处理没有封装好)
 */
public class JPAUtil {

    private static EntityManagerFactory factory=null;

    static{
        factory = Persistence.createEntityManagerFactory("myJpa");
    }

    /**
     * 获取EntityManager
     * @return
     */
    public static EntityManager getEntityManager(){
        return factory.createEntityManager();
    }

    /**
     * 关闭资源
     * @param factory
     * @param em
     */
    public static void clodeResources(EntityManagerFactory factory,EntityManager em){
        em.close();
        factory.close();
    }
}

###2.查询全部

//查询所有客户
@Test
public void findAll() {
    EntityManager em = null;
    EntityTransaction tx = null;
    try {
        //获取实体管理对象
        em = JPAUtil.getEntityManager();
        //获取事务对象
        tx = em.getTransaction();
        tx.begin();
        // 创建query对象
        String jpql = "from Customer";
        Query query = em.createQuery(jpql);
        // 查询并得到返回结果
        List list = query.getResultList(); // 得到集合返回类型
        for (Object object : list) {
            System.out.println(object);
        }
        tx.commit();
    } catch (Exception e) {
        // 回滚事务
        tx.rollback();
        e.printStackTrace();
    } finally {
        // 释放资源
        em.close();
    }
}

3.分页查询

    /**
     * 测试分页查询
     */
    @Test
    public void testPage(){
        EntityManager em = JPAUtil.getEntityManager();

        Query query = em.createQuery("select count(id) from Customer");
        Integer totalCount =  Integer.parseInt(query.getSingleResult().toString());    //查询一个结果
        System.out.println("数据库的总数是："+totalCount);

        int pageIndex=4;
        int pageSize=3;
        int pageCount=totalCount%pageSize==0?(totalCount/pageSize):(totalCount/pageSize+1);

        Query query1 = em.createQuery("from Customer ");
        query1.setFirstResult((pageIndex-1)*pageSize);//设置开始查询的位置
        query1.setMaxResults(pageSize); //设置每页查询的大小

        System.out.println("当前页码:"+pageIndex);
        System.out.println("每页大小:"+pageSize);
        System.out.println("总页数:"+pageCount);
        System.out.println("总条数:"+totalCount);

        List<Customer> list = query1.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
    }

4.条件查询

    /**
     * 条件查询
     * 假设需要查询 年龄大于等于18 并小于等于40
     */
    @Test
    public void testQuery1(){
        EntityManager em = JPAUtil.getEntityManager();

        Query query = em.createQuery("from Customer where age>=? and age<=?");//JPSQL语句 此处非SQL语句！
        query.setParameter(1,18);
        query.setParameter(2,40);

        List<Customer> list = query.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        JPAUtil.clodeResources(em);
    }

    /**
     * 条件查询
     * 假设需要查询 年龄大于等于18 并小于等于40
     * 按照下标占位
     */
    @Test
    public void testQuery2(){
        EntityManager em = JPAUtil.getEntityManager();

        Query query = em.createQuery("from Customer where age>=?1 and age<=?2");//JPSQL语句 此处非SQL语句！
        query.setParameter(1,18);
        query.setParameter(2,40);

        List<Customer> list = query.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        JPAUtil.clodeResources(em);
    }

    /**
     * 条件查询
     * 假设需要查询 年龄大于等于18 并小于等于40
     * 按照位置占位符
     */
    @Test
    public void testQuery3(){
        EntityManager em = JPAUtil.getEntityManager();

        Query query = em.createQuery("from Customer where age>=:XXX and age<=:OOO");//JPSQL语句 此处非SQL语句！
        query.setParameter("OOO",40);
        query.setParameter("XXX",18);

        List<Customer> list = query.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        JPAUtil.clodeResources(em);
    }

    /**
     * 模糊查询
     */
    @Test
    public void testQuery4(){
        EntityManager em = JPAUtil.getEntityManager();

        Query query = em.createQuery("from Customer where lastName like ?1");//JPSQL语句 此处非SQL语句！
        query.setParameter(1,"%小%");

        List<Customer> list = query.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        JPAUtil.clodeResources(em);
    }

5.排序查询

//根据客户id倒序查询所有客户
//查询所有客户
@Test
public void testOrder() {
    EntityManager em = null;
    EntityTransaction tx = null;
    try {
        //获取实体管理对象
        em = JPAUtil.getEntityManager();
        //获取事务对象
        tx = em.getTransaction();
        tx.begin();
        // 创建query对象
        String jpql = "from Customer order by id desc,age asc";
        Query query = em.createQuery(jpql);
        // 查询并得到返回结果
        List list = query.getResultList(); // 得到集合返回类型
        for (Object object : list) {
            System.out.println(object);
        }
        tx.commit();
    } catch (Exception e) {
        // 回滚事务
        tx.rollback();
        e.printStackTrace();
    } finally {
        // 释放资源
        em.close();
    }
}


    /**
     * 查询年龄最大的前三个人
     */
    @Test
    public void testMax(){
        EntityManager em = JPAUtil.getEntityManager();
        Query query = em.createQuery("from Customer order by age desc");//JPSQL语句 此处非SQL语句！
        query.setMaxResults(3); //查询3条

        List<Customer> list = query.getResultList();
        for (Customer customer : list) {
            System.out.println(customer);
        }
        JPAUtil.clodeResources(em);
    }

6.统计查询

//统计查询
@Test
public void findCount() {
	EntityManager em = null;
	EntityTransaction tx = null;
	try {
		//获取实体管理对象
		em = JPAUtil.getEntityManager();
		//获取事务对象
		tx = em.getTransaction();
		tx.begin();
		// 查询全部客户
		// 1.创建query对象
		String jpql = "select count(custId) from Customer";
		Query query = em.createQuery(jpql);
		// 2.查询并得到返回结果
		Object count = query.getSingleResult(); // 得到集合返回类型
		System.out.println(count);
		tx.commit();
	} catch (Exception e) {
		// 回滚事务
		tx.rollback();
		e.printStackTrace();
	} finally {
		// 释放资源
		em.close();
	}
}



 /**
   * 查询表中年龄最大值和最小值
  */
@Test
public void testQueryByAge(){
    EntityManager em = JPAUtil.getEntityManager();

    Query query = em.createQuery("select max(age),min(age) from  Customer");
    Object[] obj = (Object[]) query.getSingleResult();//结果一条

    System.out.println("最大年龄:"+obj[0]);
    System.out.println("最小年龄:"+obj[1]);
}

/**
  * 查询所有人的姓名和年龄
  */
@Test
public void testQueryName(){
    EntityManager em = JPAUtil.getEntityManager();

    Query query = em.createQuery("select lastName,age from Customer");
    List<Object[]> list = query.getResultList();
    for (Object[] obj : list) {
        System.out.println(obj[0]+"----"+obj[1]);
    }
}