Hibernate关系映射之many-to-many
Posted SaraMorning
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1、建表
2、创建实体类及映射文件
Student.java类
1 public class Student implements java.io.Serializable { 2 3 // Fields 4 5 private Integer sid; 6 private String sname; 7 private Set<Teacher> teachers=new HashSet<Teacher>(); 8 9 // Constructors 10 11 /** default constructor */ 12 public Student() { 13 } 14 15 /** full constructor */ 16 public Student(String sname) { 17 this.sname = sname; 18 } 19 20 // Property accessors 21 22 public Integer getSid() { 23 return this.sid; 24 } 25 26 public void setSid(Integer sid) { 27 this.sid = sid; 28 } 29 30 public String getSname() { 31 return this.sname; 32 } 33 34 public void setSname(String sname) { 35 this.sname = sname; 36 } 37 38 public Set<Teacher> getTeachers() { 39 return teachers; 40 } 41 42 public void setTeachers(Set<Teacher> teachers) { 43 this.teachers = teachers; 44 } 45 }
使用多对多注解应该是：
@ManyToMany
@JoinTable(name="teacher_student",joinColumns={@JoinColumn(name="sid")},inverseJoinColumns={@JoinColumn(name="tid")})
public Set<Teacher> getTeachers() {
return teachers;
}
Teacher.java类
1 public class Teacher implements java.io.Serializable { 2 3 // Fields 4 5 private Integer tid; 6 private String tname; 7 private Set<Student> students=new HashSet<Student>(); 8 9 // Constructors 10 11 /** default constructor */ 12 public Teacher() { 13 } 14 15 /** full constructor */ 16 public Teacher(String tname) { 17 this.tname = tname; 18 } 19 20 // Property accessors 21 22 public Integer getTid() { 23 return this.tid; 24 } 25 26 public void setTid(Integer tid) { 27 this.tid = tid; 28 } 29 30 public String getTname() { 31 return this.tname; 32 } 33 34 public void setTname(String tname) { 35 this.tname = tname; 36 } 37 38 public Set<Student> getStudents() { 39 return students; 40 } 41 42 public void setStudents(Set<Student> students) { 43 this.students = students; 44 } 45 }
被控方注解是：
@ManyToMany(mappedBy="teachers")
public Set<Student> getStudents() {
return students;
}
Student.hbm.xml
<hibernate-mapping> <class name="com.db.Student" table="student" catalog="mydb"> <id name="sid" type="java.lang.Integer"> <column name="sid" /> <generator class="native" /> </id> <property name="sname" type="java.lang.String"> <column name="sname" length="32" /> </property> <!-- 通过table属性告诉hibernate中间表，cascade指明级联操作的类型，inverse属性说明Student实体类是主控方，负责维护关系表 --> <set name="teachers" table="teacher_student" cascade="save-update,delete" inverse="false"> <!-- 通过key属性告诉hibernate在中间表里面查询sid值相应的student记录 --> <key> <column name="sid" not-null="true" /> </key> <!-- 通过column项告诉hibernate对teacher表中查找tid值相应的teacher记录 --> <many-to-many class="com.db.Teacher" column="tid"/> </set> </class> </hibernate-mapping>
Teacher.hbm.xml
<hibernate-mapping> <class name="com.db.Teacher" table="teacher" catalog="mydb"> <id name="tid" type="java.lang.Integer"> <column name="tid" /> <generator class="native" /> </id> <property name="tname" type="java.lang.String"> <column name="tname" length="32" /> </property> <!-- 通过table属性告诉hibernate中间表，cascade指明级联操作的类型，inverse属性说明Teacher实体类是被控方，不负责维护关系表 ，不能触发对象和数据库的同步更新的。--> <set name="students" table="teacher_student" inverse="true" cascade="save-update,delete"> <key> <column name="tid" not-null="true" /> </key> <many-to-many class="com.db.Student" column="sid" /> </set> </class> </hibernate-mapping>
hibernate.cfg.xml
<hibernate-configuration> <session-factory> <property name="dialect"> org.hibernate.dialect.mysqlInnoDBDialect </property> <property name="connection.url"> jdbc:mysql://localhost:3306/mydb </property> <property name="connection.username">root</property> <property name="connection.password">123456</property> <property name="connection.driver_class"> com.mysql.jdbc.Driver </property> <property name="myeclipse.connection.profile"> MyDBAccount </property> <property name="show_sql">true</property> <mapping resource="com/db/Student.hbm.xml" /> <mapping resource="com/db/Teacher.hbm.xml" /> </session-factory> </hibernate-configuration>
3、建立测试用例
测试用例一：
public static void main(String[] args) { // TODO Auto-generated method stub Session session=HibernateSessionFactory.getSession(); Student stu1=new Student(); stu1.setSname("StudentAmy"); Teacher t1=new Teacher(); t1.setTname("TeacherSusan"); Teacher t2=new Teacher(); t2.setTname("TeacherLily"); Teacher t3=new Teacher(); t3.setTname("TeacherMaike"); Set<Teacher> teachers=new HashSet<Teacher>(); teachers.add(t1); teachers.add(t2); teachers.add(t3); stu1.setTeachers(teachers); session.save(stu1); session.getTransaction().commit(); }
对应的SQL语句是：
Hibernate: insert into mydb.student (sname) values (?)
Hibernate: insert into mydb.teacher (tname) values (?)
Hibernate: insert into mydb.teacher (tname) values (?)
Hibernate: insert into mydb.teacher (tname) values (?)
Hibernate: insert into teacher_student (sid, tid) values (?, ?)
Hibernate: insert into teacher_student (sid, tid) values (?, ?)
Hibernate: insert into teacher_student (sid, tid) values (?, ?)
测试用例二：
public static void main(String[] args) { // TODO Auto-generated method stub Session session=HibernateSessionFactory.getSession(); Student stu1=new Student(); stu1.setSname("StudentJhon1"); Student stu2=new Student(); stu2.setSname("StudentLihua1"); Teacher t1=new Teacher(); t1.setTname("TeacherJay1"); t1.getStudents().add(stu1); t1.getStudents().add(stu2); session.beginTransaction(); session.save(t1); session.getTransaction().commit(); } }
对应的SQL语句是：
Hibernate: insert into mydb.teacher (tname) values (?)
Hibernate: insert into mydb.student (sname) values (?)
Hibernate: insert into mydb.student (sname) values (?)
测试用例三：
public static void main(String[] args) { // TODO Auto-generated method stub Session session=HibernateSessionFactory.getSession(); Student stu1=new Student(); stu1.setSname("StudentJhon1"); Student stu2=new Student(); stu2.setSname("StudentLihua1"); Teacher t1=new Teacher(); t1.setTname("TeacherJay1"); t1.getStudents().add(stu1); t1.getStudents().add(stu2); stu2.getTeachers().add(t1); session.beginTransaction(); session.save(t1); session.getTransaction().commit(); } }
对应的SQL语句是：
Hibernate: insert into mydb.teacher (tname) values (?)
Hibernate: insert into mydb.student (sname) values (?)
Hibernate: insert into mydb.student (sname) values (?)
Hibernate: insert into teacher_student (sid, tid) values (?, ?)
通过测试用例发现，两个实体类都进行了级联操作，但是只有将Teacher实体对象添加到Student的teachers属性集合中时才能更新维护中间表。因为Student中的teachers集合的inverse属性是false，使得Student类成为主控方，负责维护关联关系；而Teacher中的students集合的inverse属性为true，使得Teacher类成为被控方，不会维护关联关系。
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