JPA和hibernate对删除操作的不同

郁闷小甜甜

在hibernate里面调用session的delete方法以后，无论这个被删除的对象有没有被人外键引用到，都可以被删除，并且此时的外键设为null，也就是说他会自动帮我们去查看他被谁引用到了。然后把引用全部去掉后，再把自己删掉。而在JPA里面，如果调用EntityManager.remove方法时，传进去的对象，有被外键引用到，则会失败。因为JPA里面的实现就是直接执行delete语句，也不管他有没有被外键引用，此时，当然会出错了。 测试时候使用的两个类分别如下： 举的例子是部门和员工的关系。一个部门可以有多个员工。然后把部门删掉的时候，员工的部门属性就为null了，不过，按照严谨来说，还是JPA的严谨一些。这样可以防止误操作，呵呵。 部门的实体对象 Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ -->/* * To change this template, choose Tools | Templates * and open the template in the editor. */ package com.hadeslee.jpaentity; import java.io.Serializable; import java.util.HashSet; import java.util.Set; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.Table; /** * * @author hadeslee */ @Entity @Table(name = "JPADepartment") public class Department implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @OneToMany(mappedBy = "department") private Set<erson> persons = new HashSet<erson>(); private String deptName; private String description; public String getDeptName() { return deptName; } public void setDeptName(String deptName) { this.deptName = deptName; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public Set<erson> getPersons() { return persons; } public void setPersons(Set<Person> persons) { this.persons = persons; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } @Override public int hashCode() { int hash = 0; hash = (id != null ? id.hashCode() : 0); return hash; } @Override public boolean equals(Object object) { // TODO: Warning - this method won't work in the case the id fields are not set if (!(object instanceof Department)) { return false; } Department other = (Department) object; if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) { return false; } return true; } @Override public String toString() { return "com.hadeslee.jpaentity.Department[id=" id "]"; } } 人员的实体对象 Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ -->/* * To change this template, choose Tools | Templates * and open the template in the editor. */ package com.hadeslee.jpaentity; import java.io.Serializable; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; import javax.persistence.Table; /** * * @author hadeslee */ @Entity @Table(name = "JPAPerson") public class Person implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Integer id; private String name; private int age; @ManyToOne private Department department; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @Override public int hashCode() { int hash = 0; hash = (id != null ? id.hashCode() : 0); return hash; } @Override public boolean equals(Object object) { // TODO: Warning - this method won't work in the case the id fields are not set if (!(object instanceof Person)) { return false; } Person other = (Person) object; if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) { return false; } return true; } @Override public String toString() { return "com.hadeslee.jpaentity.Person[id=" id "]"; } } [1] [2] 由于JPA是不需要配置的，代码里面已经包括了注释，所以下面附上Hibernate的映射文件，为了使数据库里面更清楚一些，所以两者使用的表不是同一张表，JPA的表是带JPA前缀的，用@Table这个注释声明了这一点。 Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ --><?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.hadeslee.jpaentity"> <class name="Department" table="Department"> <id name="id" column="departId" type="long"> <generator class="native"/> </id> <property name="deptName"/> <property name="description"/> <set name="persons"> <key column="deptId"/> <one-to-many class="Person"/> </set> </class> <class name="Person" table="Person"> <id name="id" column="personId" type="long"> <generator class="native"/> </id> <property name="name"/> <property name="age"/> <many-to-one name="department" column="deptId" class="Department"/> </class> </hibernate-mapping> 调用JPA的代码如下： Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ --> EntityManagerFactory emf = Persistence.createEntityManagerFactory("TestSSH1PU2"); EntityManager em = emf.createEntityManager(); em.getTransaction().begin(); com.hadeslee.jpaentity.Person p = new com.hadeslee.jpaentity.Person(); p.setAge(26); p.setName("千里冰封"); com.hadeslee.jpaentity.Department dept = em.find(com.hadeslee.jpaentity.Department.class, Long.valueOf("3")); System.out.println("找到的dept=" dept); em.remove(dept); em.getTransaction().commit(); 调用hibernate的代码如下： Code highlighting produced by Actipro CodeHighlighter (freeware) http://www.CodeHighlighter.com/ -->Session session = HibernateUtil.getSessionFactory().getCurrentSession(); session.getTransaction().begin(); Department dept = (Department) session.load(Department.class, 2); session.delete(dept); session.getTransaction().commit(); 最后发现是JPA是不能删除的，而hibernate这边的调用可以删除，一开始我还以为是toplink的实现问题，后来特意把实现改成hibernate的实现，也同样。所以有可能是JPA的要求必须得这样做，不能替我们自动完成一些东西，是利于安全。这可能就是标准和流行的差别吧。呵呵。 上一页 [1] [2]