JPA学习（二）

package com.atguigu.jpa.test;

import java.util.Date;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.persistence.Query;

import org.hibernate.ejb.QueryHints;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.atguigu.jpa.helloworld.Category;
import com.atguigu.jpa.helloworld.Customer;
import com.atguigu.jpa.helloworld.Department;
import com.atguigu.jpa.helloworld.Item;
import com.atguigu.jpa.helloworld.Manager;
import com.atguigu.jpa.helloworld.Order;

public class JPATest {

	private EntityManagerFactory entityManagerFactory;
	private EntityManager entityManager;
	private EntityTransaction transaction;
	
	@Before
	public void init(){
		entityManagerFactory = Persistence.createEntityManagerFactory("jpa-1");
		entityManager = entityManagerFactory.createEntityManager();
		transaction = entityManager.getTransaction();
		transaction.begin();
	}
	
	@After
	public void destroy(){
		transaction.commit();
		entityManager.close();
		entityManagerFactory.close();
	}
	
	//可以使用 JPQL 完成 UPDATE 和 DELETE 操作. 
	@Test
	public void testExecuteUpdate(){
		String jpql = "UPDATE Customer c SET c.lastName = ? WHERE c.id = ?";
		Query query = entityManager.createQuery(jpql).setParameter(1, "YYY").setParameter(2, 12);
		
		query.executeUpdate();
	}

	//使用 jpql 内建的函数
	@Test
	public void testJpqlFunction(){
		String jpql = "SELECT lower(c.email) FROM Customer c";
		
		List emails = entityManager.createQuery(jpql).getResultList();
		System.out.println(emails);
	}
	
	@Test
	public void testSubQuery(){
		//查询所有 Customer 的 lastName 为 YY 的 Order
		String jpql = "SELECT o FROM Order o "
				+ "WHERE o.customer = (SELECT c FROM Customer c WHERE c.lastName = ?)";
		
		Query query = entityManager.createQuery(jpql).setParameter(1, "YY");
		List orders = query.getResultList();
		System.out.println(orders.size());
	}
	
	/**
	 * JPQL 的关联查询同 HQL 的关联查询. 
	 */
	@Test
	public void testLeftOuterJoinFetch(){
		String jpql = "FROM Customer c LEFT OUTER JOIN FETCH c.orders WHERE c.id = ?";
		
		Customer customer = 
				(Customer) entityManager.createQuery(jpql).setParameter(1, 12).getSingleResult();
		System.out.println(customer.getLastName());
		System.out.println(customer.getOrders().size());
		
//		List result = entityManager.createQuery(jpql).setParameter(1, 12).getResultList();
//		System.out.println(result);
	}
	
	//查询 order 数量大于 2 的那些 Customer
	@Test
	public void testGroupBy(){
		String jpql = "SELECT o.customer FROM Order o "
				+ "GROUP BY o.customer "
				+ "HAVING count(o.id) >= 2";
		List customers = entityManager.createQuery(jpql).getResultList();
		
		System.out.println(customers);
	}
	
	@Test
	public void testOrderBy(){
		String jpql = "FROM Customer c WHERE c.age > ? ORDER BY c.age DESC";
		Query query = entityManager.createQuery(jpql).setHint(QueryHints.HINT_CACHEABLE, true);
		
		//占位符的索引是从 1 开始
		query.setParameter(1, 1);
		List customers = query.getResultList();
		System.out.println(customers.size());
	}
	
	//使用 hibernate 的查询缓存. 
	@Test
	public void testQueryCache(){
		String jpql = "FROM Customer c WHERE c.age > ?";
		Query query = entityManager.createQuery(jpql).setHint(QueryHints.HINT_CACHEABLE, true);
		
		//占位符的索引是从 1 开始
		query.setParameter(1, 1);
		List customers = query.getResultList();
		System.out.println(customers.size());
		
		query = entityManager.createQuery(jpql).setHint(QueryHints.HINT_CACHEABLE, true);
		
		//占位符的索引是从 1 开始
		query.setParameter(1, 1);
		customers = query.getResultList();
		System.out.println(customers.size());
	}
	
	//createNativeQuery 适用于本地 SQL
	@Test
	public void testNativeQuery(){
		String sql = "SELECT age FROM jpa_cutomers WHERE id = ?";
		Query query = entityManager.createNativeQuery(sql).setParameter(1, 3);
		
		Object result = query.getSingleResult();
		System.out.println(result);
	}
	
	//createNamedQuery 适用于在实体类前使用 @NamedQuery 标记的查询语句
	@Test
	public void testNamedQuery(){
		Query query = entityManager.createNamedQuery("testNamedQuery").setParameter(1, 3);
		Customer customer = (Customer) query.getSingleResult();
		
		System.out.println(customer);
	}
	
	//默认情况下, 若只查询部分属性, 则将返回 Object[] 类型的结果. 或者 Object[] 类型的 List.
	//也可以在实体类中创建对应的构造器, 然后再 JPQL 语句中利用对应的构造器返回实体类的对象.
	@Test
	public void testPartlyProperties(){
		String jpql = "SELECT new Customer(c.lastName, c.age) FROM Customer c WHERE c.id > ?";
		List result = entityManager.createQuery(jpql).setParameter(1, 1).getResultList();
		
		System.out.println(result);
	}
	
	@Test
	public void testHelloJPQL(){
		String jpql = "FROM Customer c WHERE c.age > ?";
		Query query = entityManager.createQuery(jpql);
		
		//占位符的索引是从 1 开始
		query.setParameter(1, 1);
		List customers = query.getResultList();
		System.out.println(customers.size());
	}
	
	@Test
	public void testSecondLevelCache(){
		Customer customer1 = entityManager.find(Customer.class, 1);
		
		transaction.commit();
		entityManager.close();
		
		entityManager = entityManagerFactory.createEntityManager();
		transaction = entityManager.getTransaction();
		transaction.begin();
		
		Customer customer2 = entityManager.find(Customer.class, 1);
	}
	
	//对于关联的集合对象, 默认使用懒加载的策略.
	//使用维护关联关系的一方获取, 还是使用不维护关联关系的一方获取, SQL 语句相同. 
	@Test
	public void testManyToManyFind(){
//		Item item = entityManager.find(Item.class, 5);
//		System.out.println(item.getItemName());
//		
//		System.out.println(item.getCategories().size());
		
		Category category = entityManager.find(Category.class, 3);
		System.out.println(category.getCategoryName());
		System.out.println(category.getItems().size());
	}
	
	//多对所的保存
	@Test
	public void testManyToManyPersist(){
		Item i1 = new Item();
		i1.setItemName("i-1");
	
		Item i2 = new Item();
		i2.setItemName("i-2");
		
		Category c1 = new Category();
		c1.setCategoryName("C-1");
		
		Category c2 = new Category();
		c2.setCategoryName("C-2");
		
		//设置关联关系
		i1.getCategories().add(c1);
		i1.getCategories().add(c2);
		
		i2.getCategories().add(c1);
		i2.getCategories().add(c2);
		
		c1.getItems().add(i1);
		c1.getItems().add(i2);
		
		c2.getItems().add(i1);
		c2.getItems().add(i2);
		
		//执行保存
		entityManager.persist(i1);
		entityManager.persist(i2);
		entityManager.persist(c1);
		entityManager.persist(c2);
	}
	
	//1. 默认情况下, 若获取不维护关联关系的一方, 则也会通过左外连接获取其关联的对象. 
	//可以通过 @OneToOne 的 fetch 属性来修改加载策略. 但依然会再发送 SQL 语句来初始化其关联的对象
	//这说明在不维护关联关系的一方, 不建议修改 fetch 属性. 
	@Test
	public void testOneToOneFind2(){
		Manager mgr = entityManager.find(Manager.class, 1);
		System.out.println(mgr.getMgrName());
		
		System.out.println(mgr.getDept().getClass().getName());
	}
	
	//1.默认情况下, 若获取维护关联关系的一方, 则会通过左外连接获取其关联的对象. 
	//但可以通过 @OntToOne 的 fetch 属性来修改加载策略.
	@Test
	public void testOneToOneFind(){
		Department dept = entityManager.find(Department.class, 1);
		System.out.println(dept.getDeptName());
		System.out.println(dept.getMgr().getClass().getName());
	}
	
	//双向 1-1 的关联关系, 建议先保存不维护关联关系的一方, 即没有外键的一方, 这样不会多出 UPDATE 语句.
	@Test
	public void testOneToOnePersistence(){
		Manager mgr = new Manager();
		mgr.setMgrName("M-BB");
		
		Department dept = new Department();
		dept.setDeptName("D-BB");
		
		//设置关联关系
		mgr.setDept(dept);
		dept.setMgr(mgr);
		
		//执行保存操作
		entityManager.persist(mgr);
		entityManager.persist(dept);
	}
	
	@Test
	public void testUpdate(){
		Customer customer = entityManager.find(Customer.class, 10);
		
		customer.getOrders().iterator().next().setOrderName("O-XXX-10");
	}
	
	//默认情况下, 若删除 1 的一端, 则会先把关联的 n 的一端的外键置空, 然后进行删除. 
	//可以通过 @OneToMany 的 cascade 属性来修改默认的删除策略. 
	@Test
	public void testOneToManyRemove(){
		Customer customer = entityManager.find(Customer.class, 8);
		entityManager.remove(customer);
	}
	
	//默认对关联的多的一方使用懒加载的加载策略. 
	//可以使用 @OneToMany 的 fetch 属性来修改默认的加载策略
	@Test
	public void testOneToManyFind(){
		Customer customer = entityManager.find(Customer.class, 9);
		System.out.println(customer.getLastName());
		
		System.out.println(customer.getOrders().size());
	}
	
	//若是双向 1-n 的关联关系, 执行保存时
	//若先保存 n 的一端, 再保存 1 的一端, 默认情况下, 会多出 n 条 UPDATE 语句.
	//若先保存 1 的一端, 则会多出 n 条 UPDATE 语句
	//在进行双向 1-n 关联关系时, 建议使用 n 的一方来维护关联关系, 而 1 的一方不维护关联系, 这样会有效的减少 SQL 语句. 
	//注意: 若在 1 的一端的 @OneToMany 中使用 mappedBy 属性, 则 @OneToMany 端就不能再使用 @JoinColumn 属性了. 
	
	//单向 1-n 关联关系执行保存时, 一定会多出 UPDATE 语句.
	//因为 n 的一端在插入时不会同时插入外键列. 
	@Test
	public void testOneToManyPersist(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("MM");
		
		Order order1 = new Order();
		order1.setOrderName("O-MM-1");
		
		Order order2 = new Order();
		order2.setOrderName("O-MM-2");
		
		//建立关联关系
		customer.getOrders().add(order1);
		customer.getOrders().add(order2);
		
		order1.setCustomer(customer);
		order2.setCustomer(customer);
		
		//执行保存操作
		entityManager.persist(customer);

		entityManager.persist(order1);
		entityManager.persist(order2);
	}
	
	/*
	@Test
	public void testManyToOneUpdate(){
		Order order = entityManager.find(Order.class, 2);
		order.getCustomer().setLastName("FFF");
	}
	
	//不能直接删除 1 的一端, 因为有外键约束. 
	@Test
	public void testManyToOneRemove(){
//		Order order = entityManager.find(Order.class, 1);
//		entityManager.remove(order);
		
		Customer customer = entityManager.find(Customer.class, 7);
		entityManager.remove(customer);
	}
	
	//默认情况下, 使用左外连接的方式来获取 n 的一端的对象和其关联的 1 的一端的对象. 
	//可使用 @ManyToOne 的 fetch 属性来修改默认的关联属性的加载策略
	@Test
	public void testManyToOneFind(){
		Order order = entityManager.find(Order.class, 1);
		System.out.println(order.getOrderName());
		
		System.out.println(order.getCustomer().getLastName());
	}
	*/
	
	/**
	 * 保存多对一时, 建议先保存 1 的一端, 后保存 n 的一端, 这样不会多出额外的 UPDATE 语句.
	 */
	/*
	@Test
	public void testManyToOnePersist(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("GG");
		
		Order order1 = new Order();
		order1.setOrderName("G-GG-1");
		
		Order order2 = new Order();
		order2.setOrderName("G-GG-2");
		
		//设置关联关系
		order1.setCustomer(customer);
		order2.setCustomer(customer);
		
		//执行保存操作
		entityManager.persist(order1);
		entityManager.persist(order2);
		
		entityManager.persist(customer);
	}
	*/
	
	/**
	 * 同 hibernate 中 Session 的 refresh 方法. 
	 */
	@Test
	public void testRefresh(){
		Customer customer = entityManager.find(Customer.class, 1);
		customer = entityManager.find(Customer.class, 1);
		
		entityManager.refresh(customer);
	}
	
	/**
	 * 同 hibernate 中 Session 的 flush 方法. 
	 */
	@Test
	public void testFlush(){
		Customer customer = entityManager.find(Customer.class, 1);
		System.out.println(customer);
		
		customer.setLastName("AA");
		
		entityManager.flush();
	}
	
	//若传入的是一个游离对象, 即传入的对象有 OID. 
	//1. 若在 EntityManager 缓存中有对应的对象
	//2. JPA 会把游离对象的属性复制到查询到EntityManager 缓存中的对象中.
	//3. EntityManager 缓存中的对象执行 UPDATE. 
	@Test
	public void testMerge4(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("DD");
		
		customer.setId(4);
		Customer customer2 = entityManager.find(Customer.class, 4);
		
		entityManager.merge(customer);
		
		System.out.println(customer == customer2); //false
	}
	
	//若传入的是一个游离对象, 即传入的对象有 OID. 
	//1. 若在 EntityManager 缓存中没有该对象
	//2. 若在数据库中也有对应的记录
	//3. JPA 会查询对应的记录, 然后返回该记录对一个的对象, 再然后会把游离对象的属性复制到查询到的对象中.
	//4. 对查询到的对象执行 update 操作. 
	@Test
	public void testMerge3(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("EE");
		
		customer.setId(4);
		
		Customer customer2 = entityManager.merge(customer);
		
		System.out.println(customer == customer2); //false
	}
	
	//若传入的是一个游离对象, 即传入的对象有 OID. 
	//1. 若在 EntityManager 缓存中没有该对象
	//2. 若在数据库中也没有对应的记录
	//3. JPA 会创建一个新的对象, 然后把当前游离对象的属性复制到新创建的对象中
	//4. 对新创建的对象执行 insert 操作. 
	@Test
	public void testMerge2(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("DD");
		
		customer.setId(100);
		
		Customer customer2 = entityManager.merge(customer);
		
		System.out.println("customer#id:" + customer.getId());
		System.out.println("customer2#id:" + customer2.getId());
	}
	
	/**
	 * 总的来说: 类似于 hibernate Session 的 saveOrUpdate 方法.
	 */
	//1. 若传入的是一个临时对象
	//会创建一个新的对象, 把临时对象的属性复制到新的对象中, 然后对新的对象执行持久化操作. 所以
	//新的对象中有 id, 但以前的临时对象中没有 id. 
	@Test
	public void testMerge1(){
		Customer customer = new Customer();
		customer.setAge(18);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("CC");
		
		Customer customer2 = entityManager.merge(customer);
		
		System.out.println("customer#id:" + customer.getId());
		System.out.println("customer2#id:" + customer2.getId());
	}
	
	//类似于 hibernate 中 Session 的 delete 方法. 把对象对应的记录从数据库中移除
	//但注意: 该方法只能移除 持久化 对象. 而 hibernate 的 delete 方法实际上还可以移除 游离对象.
	@Test
	public void testRemove(){
//		Customer customer = new Customer();
//		customer.setId(2);
		
		Customer customer = entityManager.find(Customer.class, 2);
		entityManager.remove(customer);
	}
	
	//类似于 hibernate 的 save 方法. 使对象由临时状态变为持久化状态. 
	//和 hibernate 的 save 方法的不同之处: 若对象有 id, 则不能执行 insert 操作, 而会抛出异常. 
	@Test
	public void testPersistence(){
		Customer customer = new Customer();
		customer.setAge(15);
		customer.setBirth(new Date());
		customer.setCreatedTime(new Date());
		customer.setEmail("[email protected]");
		customer.setLastName("BB");
		customer.setId(100);
		
		entityManager.persist(customer);
		System.out.println(customer.getId());
	}
	
	//类似于 hibernate 中 Session 的 load 方法
	@Test
	public void testGetReference(){
		Customer customer = entityManager.getReference(Customer.class, 1);
		System.out.println(customer.getClass().getName());
		
		System.out.println("-------------------------------------");
//		transaction.commit();
//		entityManager.close();
		
		System.out.println(customer);
	}
	
	//类似于 hibernate 中 Session 的 get 方法. 
	@Test
	public void testFind() {
		Customer customer = entityManager.find(Customer.class, 1);
		System.out.println("-------------------------------------");
		
		System.out.println(customer);
	}

}