08-hibernate注解-多对多单向外键关联

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多对多单向外键

1,学生和教师构成多对多的关联关系

2,其中 一个多方持有另一个多方的集合对象 （ 学生持有教室的集合 ）

3，通过注解@JoinTable，创建中间表（作为多对多的载体，用来确定学生和教师的多对多关系）

@JoinTable(

            name="teachars_students",                    //中间表的名字

            joinColumns= {@JoinColumn(name="sid")},        //外键的字段

            inverseJoinColumns= {@JoinColumn(name="tid")})    //反转控制字段的名字

最后会自动创建一个中间表teachars_students，并且这个表包含两个字段，sid和tid,并且这两个字段也是这个中间表的外键。

学生类：

1，这里学生持有教师的集合，所以学生类里面需要一个教师集合属性 。

2，指定多对多注解： @ManyToMany

3，指定中间表注解：并分别指定学生类的主键 sid，教师类的主键 tid。 @JoinTable

package mtm_fk;

import java.util.Date;

import java.util.Set;

import javax.persistence.CascadeType;

import javax.persistence.Entity;/*JPA主键*/

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

/*学生实体类*/

@Entity

@Table(name="Students",schema="sys")

public class Students {

    private int sid;

    private String name;

    private String gender;//性别

    private Date birthday;

    private String major;//专业

    private Set<Teachers> teachers;//学生持有教师的集合

    public Students()

    {

    }

    public Students( String name,String gender, Date birthday, String major) {

        //super();

        this.name=name;

        this.gender = gender;

        this.birthday = birthday;

        this.major = major;

    }

    @Id

    @GeneratedValue //主键自动增长

    public int getSid() {

        return sid;

    }

    public void setSid(int sid) {

        this.sid = sid;

    }

    public String getGender() {

        return gender;

    }

    public void setGender(String gender) {

        this.gender = gender;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Date getBirthday() {

        return birthday;

    }

    public void setBirthday(Date birthday) {

        this.birthday = birthday;

    }

    public String getMajor() {

        return major;

    }

    public void setMajor(String major) {

        this.major = major;

    }

    @ManyToMany

    @JoinTable(

            name="teachars_students",                    //中间表的名字

            joinColumns= {@JoinColumn(name="sid")},        //外键的字段

            inverseJoinColumns= {@JoinColumn(name="tid")})    //反转控制字段的名字

    public Set<Teachers> getTeachers() {

        return teachers;

    }

    public void setTeachers(Set<Teachers> teachers) {

        this.teachers = teachers;

    }

}

教师类：

package mtm_fk;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import org.hibernate.annotations.GenericGenerator;

//教室实体类

@Entity

public class Teachers {

    @Id

    @GeneratedValue(generator="tid")

    @GenericGenerator(name="tid",strategy="assigned")

    @Column(length=4)

    private String tid;//教师的编号

    private String tname;//姓名

    public Teachers()

    {

    }

    public Teachers(String tid, String tname) {

        //super();

        this.tid = tid;

        this.tname = tname;

    }

    public String getTid() {

        return tid;

    }

    public void setTid(String tid) {

        this.tid = tid;

    }

    public String getTname() {

        return tname;

    }

    public void setTname(String tname) {

        this.tname = tname;

    }

}

测试类：

package mtm;

import java.util.Date;

import java.util.EnumSet;

import java.util.HashSet;

import java.util.Set;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.boot.Metadata;

import org.hibernate.boot.MetadataSources;

import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

import org.hibernate.cfg.Configuration;

import org.hibernate.service.ServiceRegistry;

import org.hibernate.tool.hbm2ddl.SchemaExport;

import org.hibernate.tool.schema.TargetType;

import org.junit.Test;

import mtm_fk.Students;

import mtm_fk.Teachers;

public class testStudents {

    @Test

    public void testSchemaExport()

    {

        //创建服务注册对象

        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();

        //创建Metadata对象

        Metadata metadata =new MetadataSources(serviceRegistry).buildMetadata();

        //创建SchemaExport对象

        SchemaExport export = new SchemaExport();

        export.create(EnumSet.of(TargetType.DATABASE),metadata);

    }

    @Test

    public void addStudetns()

    {

        Configuration config=new Configuration().configure();

        //创建服务注册对象。

        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();

        //创建会话工厂对象

        SessionFactory sessionFactory=config.buildSessionFactory(serviceRegistry);

        //创建会话对象

        Session session=sessionFactory.openSession();

        //开启事务

        Transaction transaction=session.beginTransaction();

        //创建教师对象

        Teachers t1=new Teachers("T001","詹老师");

        Teachers t2=new Teachers("T002","刘老师");

        Teachers t3=new Teachers("T003","张老师");

        Teachers t4=new Teachers("T004","陈老师");

        //创建学生对象

        Students s1=new Students("张三","男",new Date(),"计算机");

        Students s2=new Students("李四","男",new Date(),"计算机");

        Students s3=new Students("王五","男",new Date(),"计算机");

        Students s4=new Students("赵六","男",new Date(),"计算机");

        Set<Teachers> set1=new HashSet<Teachers>();

        set1.add(t1);

        set1.add(t2);

        Set<Teachers> set2=new HashSet<Teachers>();

        set2.add(t3);

        set2.add(t4);

        Set<Teachers> set3=new HashSet<Teachers>();

        set3.add(t1);

        set2.add(t3);

        set3.add(t4);

        Set<Teachers> set4=new HashSet<Teachers>();

        set3.add(t1);

        set4.add(t2);

        set4.add(t4);

        s1.setTeachers(set1);

        s2.setTeachers(set2);

        s3.setTeachers(set3);

        s4.setTeachers(set4);

        session.save(t1);

        session.save(t2);

        session.save(t3);

        session.save(t4);

        session.save(s1);

        session.save(s2);

        session.save(s3);

        session.save(s4);

        transaction.commit();

    }

}