存在如下表，考虑多对一和一对多的配置
多对一，如何在多的一端配置 从多的一端获取一的一端的数据 student
public class Student { private int id; private String name; private int age; private Grade grade; //get…set }Grade
public class Grade { private int id; private String name; //get…set }Grade.hbm.xml
<hibernate-mapping package="cn.siggy.pojo"> <class name="Grade"> <id name="id"> <generator class="native"></generator> </id> <property name="name"/> </class> </hibernate-mapping>Student.hbm.xml
<hibernate-mapping package="cn.siggy.pojo"> <class name="Student"> <id name="id"> <generator class="native"></generator> </id> <property name="name"/> <property name="age"/> <!-- 多对一 name 表示属性名 class 指明 属性对应的类 column指 数据库表中的列名 --> <many-to-one name="grade" class="Grade" column="grade_id" foreign-key="fk_grade" not-null="true"/> </class> </hibernate-mapping>测试（session对象的获取封装在HibernateUtil，略）
@Test public void testSave() throws HibernateException, SerialException, SQLException{ Session session = null; Transaction tx = null; try{ session = HibernateUtil.getSession(); tx = session.beginTransaction(); Grade grade = new Grade(); grade.setName("基础"); session.save(grade); Student stu = new Student(); stu.setName("张三疯"); stu.setAge(22); stu.setGrade(grade); session.save(stu); tx.commit(); }catch (HibernateException e) { if(tx!=null) tx.rollback(); e.printStackTrace(); throw e; }finally{ HibernateUtil.closeSession(); } }一对多 在一的一端配置 从一的一端获取多的一端的数据 用集合表示 Student
public class Student { private int id; private String name; private int age; //get…set }Grade
public class Grade { private int id; private String name; private Set<Student> students = new HashSet<Student>(0); //get…set }Grade.hbm.xml
<hibernate-mapping package="cn.siggy.pojo"> <class name="Grade"> <id name="id"> <generator class="native"></generator> </id> <property name="name"/> <!-- set是 Grade中的集合属性 name属性名称 --> <set name="students"> <!-- key表示外键 column外键列名--> <key column="grade_id" not-null="true"></key> <!-- one-to-many 一对多 类Grade 中 students 所表示类型 --> <one-to-many class="Student"/> </set> </class> </hibernate-mapping>student.hbm.xml
<hibernate-mapping package="cn.siggy.pojo"> <class name="Student"> <id name="id"> <generator class="native"></generator> </id> <property name="name"/> <property name="age"/> </class> </hibernate-mapping>测试
session = HibernateUtil.getSession(); tx = session.beginTransaction(); Grade grade = new Grade(); grade.setName("基础"); Student stu = new Student(); stu.setName("张三疯"); stu.setAge(22); Student stu1 = new Student(); stu1.setName("老王"); stu1.setAge(23); //关联 grade.getStudents().add(stu); grade.getStudents().add(stu1); //保存数据的顺序 是根据外键的配置来决定的 //如果外键不能为null,那么先保存一的一端 //如果外键可以为null,则可以随意保存 session.save(grade); session.save(stu); session.save(stu1); tx.commit(); session = HibernateUtil.getSession(); tx = session.beginTransaction(); //取数据 Grade grade = (Grade)session.get(Grade.class, 1); System.out.println("gradeName="+grade.getName()); System.out.println("grade所对应的多的一端的数据"); Iterator<Student> iter = grade.getStudents().iterator(); for(;iter.hasNext();){ Student temp = iter.next(); System.out.println("name="+temp.getName()+"\tage="+temp.getAge()); } tx.commit();