Hibernate 再接触 多对多单向双向关联

情景：一个老师可能有多个学生，一个学生也可能有多个老师

多对一单向：

例如老师知道自己教哪些学生，学生却不知道自己被哪些老师教

方法：使用第三张表 分别存两张表的id

annotation

Student.java

package com.bjsxt.hibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
public class Student {
    private int id;
    private String name;
    
    @Id
    @GeneratedValue
    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;
    }
}

Teacher.java

package com.bjsxt.hibernate;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
public class Teacher {
    private int id;
    private String name;
    private Set<Student> students = new HashSet<Student>();
    @Id
    @GeneratedValue
    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;
    }
    @ManyToMany
    @JoinTable(name="t_s",
        joinColumns={@JoinColumn(name="teacher_id")},    //自己这个类的外键id
        inverseJoinColumns={@JoinColumn(name="student_id")}   //对方那张表的外键id
        )
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

XML

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Student">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
    </class>
    
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Teacher">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
        <set name="students" table="t_s">
            <key column="teacher_id"></key>
            <many-to-many class="com.bjsxt.hibernate.Student" column="student_id"/>
        </set>
    </class>
    
</hibernate-mapping>

test

@Test
    public void testSchemaExport() {
        new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
    }

多对多 双向关联  必设mapped

老师知道自己教那些学生 学生知道被哪些老师教

ANNOTATION

Student.java

package com.bjsxt.hibernate;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entity
public class Student {
    private int id;
    private String name;
    private Set<Teacher> teachers = new HashSet<Teacher>();
    @ManyToMany(mappedBy="students")
    public Set<Teacher> getTeachers() {
        return teachers;
    }
    public void setTeachers(Set<Teacher> teachers) {
        this.teachers = teachers;
    }
    @Id
    @GeneratedValue
    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;
    }
}

Teacher.java

package com.bjsxt.hibernate;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entity
public class Student {
    private int id;
    private String name;
    private Set<Teacher> teachers = new HashSet<Teacher>();
    @ManyToMany(mappedBy="students")
    public Set<Teacher> getTeachers() {
        return teachers;
    }
    public void setTeachers(Set<Teacher> teachers) {
        this.teachers = teachers;
    }
    @Id
    @GeneratedValue
    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;
    }
}

XML

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Student">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
        <set name="teachers" table="t_s">
            <key column="student_id"></key>
            <many-to-many class="com.bjsxt.hibernate.Teacher" column="teacher_id"/>
        </set>
    </class>
    
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Teacher">
        <id name="id">
            <generator class="native"></generator>
        </id>
        
        <property name="name"></property>
        <set name="students" table="t_s">
            <key column="teacher_id"></key>
            <many-to-many class="com.bjsxt.hibernate.Student" column="student_id"/>
        </set>
    </class>
    
</hibernate-mapping>

test

    @Test
    public void testSchemaExport() {
        new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
    }