Hibernate学习（四）

映射关系（关联映射，使用xml文件进行配置）
（1）一对一映射（一个公司对应一个地址，地址和公司的关系是一对一）第一步：建立类公司类：//一对一 xml配置public class CompanyXML {private int id;private String name;private AddressXML addressId;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public AddressXML getAddressId() {return addressId;}public void setAddressId(AddressXML addressId) {this.addressId = addressId;}}地址类：//一对一 xml配置public class AddressXML { private int id;private String city;private String country;private CompanyXML companyXML;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getCity() {return city;}public void setCity(String city) {this.city = city;}public String getCountry() {return country;}public void setCountry(String country) {this.country = country;}public void setCompanyXML(CompanyXML companyXML) {this.companyXML = companyXML;}public CompanyXML getCompanyXML() {return companyXML;}} 第二步：映射文件公司类映射文件：（CompanyXML.hbm.xml）<hibernate-mapping package="hibernate.test.domain"> <class name="CompanyXML" table="companyXML" lazy="true"><id name="id"><generator class="native"></generator></id><property name="name"></property><many-to-one name="addressId" class="AddressXML" cascade="all" unique="true"><column name="address"></column></many-to-one><!-- <one-to-one name="addressId" class="AddressXML" property-ref="companyXML" cascade="all"></one-to-one> --></class></hibernate-mapping>地址类映射文件（AddressXML.hbm.xml）：<hibernate-mapping package="hibernate.test.domain"> <class name="AddressXML" table="addressXML" lazy="true"><id name="id"><generator class="native"></generator></id><property name="city"></property><property name="country"></property><one-to-one name="companyXML" class="CompanyXML" property-ref="addressId" cascade="all"></one-to-one></class></hibernate-mapping>说明： 基于外键的1――1关联，外键可以存放在任意一端， 1、 存放的一端要增加many-to-one元素，并添加unique=”true“，column="映射到本表的字段名" 2、另一端使用one-to-one元素，使用property-ref指定引用关联类的属性；第三步：配置文件（hibernate.cfg.xml）添加两个映射：<mapping resource="hibernate/test/xml/AddressXML.hbm.xml"></mapping> <mapping resource="hibernate/test/xml/CompanyXML.hbm.xml"></mapping>第四步：测试public static void main(String[] args) {// TODO Auto-generated method stubSession session=null;Transaction tx=null;try {session=HibernateAnnocationUtil.getSession();tx=session.beginTransaction();AddressXML addressXML=new AddressXML();addressXML.setCity("zhengzhou2");addressXML.setCountry("zhengzhou1");CompanyXML companyXML=new CompanyXML();companyXML.setName("yizhilian");companyXML.setAddressId(addressXML);session.save(companyXML);tx.commit();} catch (Exception e) {// TODO: handle exceptionif(tx!=null){tx.rollback();}throw e;}finally{if(session!=null){session.close();}}（2）一对多映射（多对一映射）第一步：建立类（一个部门中有多个员工，部门与员工之间是一对多的关系）部门类：public class Department {private int deptid;private String dname;private String location;private Set<Employee> employees=new HashSet<Employee>();public int getDeptid() {return deptid;}public void setDeptid(int deptid) {this.deptid = deptid;}public String getDname() {return dname;}public void setDname(String dname) {this.dname = dname;}public String getLocation() {return location;}public void setLocation(String location) {this.location = location;}public Set<Employee> getEmployees() {return employees;}public void setEmployees(Set<Employee> employees) {this.employees = employees;}} 员工类：public class Employee {private int id;private String name;private String job;private Department department;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getJob() {return job;}public void setJob(String job) {this.job = job;}public void setDepartment(Department department) {this.department = department;}public Department getDepartment() {return department;}}第二步：映射文件部门类映射文件（Department.hbm.xml）：<hibernate-mapping package="hibernate.test.domain"> <class name="Department" table="Department" lazy="true"><id name="deptid"><generator class="native"></generator></id><property name="dname" type="java.lang.String"></property><property name="location" type="java.lang.String"></property><set name="employees" cascade="save-update" inverse="true"><key><column name="department"></column></key><one-to-many class="Employee"></one-to-many><!-- 表明关系 --></set></class></hibernate-mapping>员工类映射文件（Employee.hbm.xml）：<hibernate-mapping package="hibernate.test.domain"> <class name="Employee" table="Employee" lazy="true"><id name="id"><column name="id"></column><generator class="native"></generator></id><property name="name" type="java.lang.String"></property><property name="job" type="java.lang.String"></property><many-to-one name="department" class="Department" cascade="save-update" ><column name="deptid"></column></many-to-one></class></hibernate-mapping>说明： 基于外键的1――N关联，外键存放在多的那一端， 1、 存放的一端（也就是多的一端）要增加many-to-one元素，column="映射到本表的字段名" （也可以不指定） 2、另一端使用set元素，使用key.column指定关联的外键列,在one-to-many中指明用以映射到关联类的属性； 第三步：配置文件（hibernate.cfg.xml） <mapping resource="hibernate/test/xml/Employee.hbm.xml"></mapping> <mapping resource="hibernate/test/xml/Department.hbm.xml"></mapping>第四步：测试public static void main(String[] args) {// TODO Auto-generated method stubSession session=null;Transaction tx=null;try {session=HibernateUtil.getSession();tx=session.beginTransaction();Department department=new Department();department.setDname("技术部");department.setLocation("zhengzhou");session.save(department);Employee employee1=new Employee();employee1.setName("张三");Employee employee2=new Employee();employee2.setName("李四");employee1.setDepartment(department);employee2.setDepartment(department);session.save(employee1);session.save(employee2);tx.commit();} catch (Exception e) {// TODO: handle exceptionif(tx!=null)tx.rollback();}finally{if(session!=null)session.close();}}
（3）多对多映射第一步：建立类（学生和课程是多对多的关系）学生类：public class StudentXML { private int id;private String name;private Set<CourseXML> courseXMLs=new HashSet<CourseXML>();public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public void setCourseXMLs(Set<CourseXML> courseXMLs) {this.courseXMLs = courseXMLs;}public Set<CourseXML> getCourseXMLs() {return courseXMLs;}
} 课程类：public class CourseXML { private int id;private String name;private Set<StudentXML> studentXMLs=new HashSet<StudentXML>();public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<StudentXML> getStudentXMLs() {return studentXMLs;}public void setStudentXMLs(Set<StudentXML> studentXMLs) {this.studentXMLs = studentXMLs;}
}第二步：映射文件学生类映射文件（StudentXML.hbm.xml）：<hibernate-mapping package="hibernate.test.domain"> <class name="StudentXML" table="studentXML" lazy="true"><id name="id"><generator class="native"></generator></id><property name="name"></property><set name="courseXMLs" table="stu_coursexml" cascade="save-update"> <!-- 指定关联的外键列 --><key column="studentId"/><!-- key.column指出本类提供中间表的字段--><many-to-many class="CourseXML" column="courseId"></many-to-many></set></class></hibernate-mapping>课程类映射文件（CourseXML.hbm.xml）：<hibernate-mapping package="hibernate.test.domain"> <class name="CourseXML" table="courseXML" lazy="true"><id name="id"><generator class="native"></generator></id><property name="name"></property><set name="studentXMLs" table="stu_coursexml" cascade="save-update"><key column="courseId"/> <!-- key.column指出本类提供中间表的字段--><many-to-many class="StudentXML" column="studentId"></many-to-many></set></class></hibernate-mapping>说明： 基于外键的N――N关联，两个表的主键作为第三张表进行存储 1、 一端使用set元素，使用key.column指出本类提供中间表的字段,在many-to-many中指明用以映射到关联类的属性，而many-to-many中的column属性指的是class类在第三张表（中间表）中的字段； 2、另一端和前面一样，需要制定本类和关联类在第三张表中的属性。两者配置时要注意属性对应，第三张表的表名一样。第三步：配置文件（hibernate.cfg.xml） <mapping resource="hibernate/test/xml/CourseXML.hbm.xml"></mapping> <mapping resource="hibernate/test/xml/StudentXML.hbm.xml"></mapping>第四步：测试public static void main(String[] args) {// TODO Auto-generated method stubSession session=null;Transaction tx=null;try {session=HibernateAnnocationUtil.getSession();tx=session.beginTransaction();
StudentXML student2=new StudentXML();student2.setName("zhangsan");StudentXML student22=new StudentXML();student22.setName("liuyang");CourseXML course=new CourseXML();course.setName("语文");//course.setName("数学");HashSet<CourseXML> courses=new HashSet<CourseXML>();courses.add(course);student2.setCourseXMLs(courses);student22.setCourseXMLs(courses);session.save(student2);session.save(student22);tx.commit();} catch (Exception e) {// TODO: handle exceptionif(tx!=null)tx.rollback();}finally{if(session!=null)session.close();}} （4）Cascade和inverse
详细见： http://www.cnblogs.com/amboyna/archive/2008/02/18/1072260.html级联指的是当主控方执行操作时，关联对象（被动方）是否同步执行同一操作。cascade定义的是关系两端对象到对象的级联关系；而inverse定义的是关系和对象的级联关系 href="http://welcomejianghome.spaces.msn.com/blog/cns!3196CAE67CDF2316!149.entry" target=_blank>Cascade：all : 所有情况下均进行关联操作。
none：所有情况下均不进行关联操作。这是默认值。
save-update:在执行save/update/saveOrUpdate时进行关联操作。
delete：在执行delete时进行关联操作。all的意思是save-update + delete
all-delete-orphan 的意思是当对象图中产生孤儿节点时,在数据库中删除该节点 Inverse：只有集合标记（set/map/list/array/bag）才有inverse属性commit后，这两个属性发挥作用的时机不同，hibernate会根据对pojo对象的改动，及cascade属性的设置，生成一系列的Action，比如UpdateAction,DeleteAction,InsertAction等，每个Action都有execute方法以执行对应的sql语句。待所有这些Action都生成好了后，hibernate再一起执行它们，在执行sql前，inverse属性起作用，
当inverse=true时，不执行sql；当inverse=false时，执行sql。 inverse的默认值为false，所以inverse属性默认会进行“关联更新”。