jpa示例源码，学习资料

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<String> 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<Order> 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<Object[]> 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<Customer> 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<Customer> 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<Customer> 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<Customer> 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); de