hibernate学习(5)——多对多关系映射
1、创建实体和映射
package com.alice.hibernate03.vo; import java.util.HashSet; import java.util.Set; public class Student { private Integer id; private String sname; private Set<Course> courses = new HashSet<Course>(); public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getSname() { return sname; } public void setSname(String sname) { this.sname = sname; } public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } }
package com.alice.hibernate03.vo; import java.util.HashSet; import java.util.Set; public class Course { private Integer id; private String cname; private Set<Student> students = new HashSet<Student>(); public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getCname() { return cname; } public void setCname(String cname) { this.cname = cname; } public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } }
2、映射
<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.alice.hibernate03.vo"> <class name="Student" table="t_student"> <id name="id" column="id"> <generator class="native"></generator> </id> <property name="sname" column="sname" type="string"></property> <!-- 多对多关系 --> <!-- set 表达集合 name: 集合的属性名 table:多对多中间表的表名 key 表达外键 column:引用我的外键名 many-to-many 表达多对多 class : 集合引用方的类型 column:对方在中间表的外键名 --> <set name="courses" table="t_student_course" inverse="false" cascade="save-update"> <!-- key 用来描述外键 column : 外键的值 --> <key column="sid"></key> <many-to-many class="Course" column="cid"></many-to-many> </set> </class> </hibernate-mapping>
<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.alice.hibernate03.vo"> <class name="Course" table="t_course"> <id name="id" column="id"> <generator class="native"></generator> </id> <property name="cname" column="cname" type="string"></property> <!-- 多对多关系 --> <!-- set 表达集合 name: 集合的属性名 table:多对多中间表的表名 key 表达外键 column:引用我的外键名 many-to-many 表达多对多 class : 集合引用方的类型 column:对方在中间表的外键名 --> <set name="students" table="t_student_course" inverse="true" cascade="save-update"> <key column="cid"></key> <many-to-many class="Student" column="sid"></many-to-many> </set> </class> </hibernate-mapping>
3、测试
package com.alice.hibernate03.many; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import com.alice.hibernate03.util.HibernateUtil; import com.alice.hibernate03.vo.Course; import com.alice.hibernate03.vo.Student; public class ManyTest { @Test public void test01(){ //保存学生 => 通过学生保存课程. 由学生维护外键 //Student 的 //inverse = false //cascade = save-update //Course //inverse = true Session session = HibernateUtil.openSession(); Transaction tran = session.beginTransaction(); //........................... Student s1 = new Student(); s1.setSname("angle"); Student s2 = new Student(); s2.setSname("echo"); Course c1 = new Course(); c1.setCname("jdbc"); Course c2 = new Course(); c2.setCname("spring"); Course c3 = new Course(); c3.setCname("strust2"); s1.getCourses().add(c1); s1.getCourses().add(c2); s2.getCourses().add(c2); s2.getCourses().add(c3); session.save(s1); session.save(s2); //........................... tran.commit(); session.close(); } }