【Hibernate】之关于多对多单向关联映射


老师和学生，最典型的多对多关联，

Teacher和Student。所谓单向意思就是说。老师知道自己的教的是哪些学生而学生不知道是哪些老师教。

也能够这么说，在查询的时候，通过老师能够级联查询出学生，可是通过学生不能够级联查询出老师。


而多对多最麻烦的是怎么自己定义我们中间表的，表名和列名，这个是重要的！




Annotations配置

@Entity
@Table(name="t_teacher")
publicclass Teacher {
    private Integer id;
    private String name;
    private Set<Student> students=new HashSet<Student>();//set不同意反复，最适合数据库模型
    @Id
    @GeneratedValue
    public Integer getId() {
       returnid;
    }
    publicvoid setId(Integerid) {
       this.id = id;
    }
    @Column(name="t_name")
    public String getName() {
       returnname;
    }
    publicvoid setName(Stringname) {
       this.name = name;
    }
    @ManyToMany
    @JoinTable(name="t_s_two",//自己定义表名
           joinColumns={@JoinColumn(name="teacher_id")},//自己定义列名
           inverseJoinColumns={@JoinColumn(name="student_id")})//反转。和Teacher相应的那个表的列名，也是自己定义
    public Set<Student>getStudents() {
       returnstudents;
    }
    publicvoidsetStudents(Set<Student> students) {
       this.students = students;
    }
}


@Entity
@Table(name="t_student")
publicclass Student {
    private Integer id;
    private String name;
    private Integer age;
    @Id
    @GeneratedValue
    public Integer getId() {
       returnid;
    }
    publicvoid setId(Integerid) {
       this.id = id;
    }
    @Column(name="s_name")
    public String getName() {
       returnname;
    }
    publicvoid setName(Stringname) {
       this.name = name;
    }
    @Column(name="s_age")
    public Integer getAge() {
       returnage;
    }
    publicvoid setAge(Integerage) {
       this.age = age;
    }
}

XML配置


publicclass Teacher {
    private Integer id;
    private String name;
    private Set<Student> students=newHashSet<Student>();//set不同意反复，最适合数据库模型
    public Integer getId() {
       returnid;
    }
    publicvoid setId(Integerid) {
       this.id = id;
    }
    public String getName() {
       returnname;
    }
    publicvoid setName(Stringname) {
       this.name = name;
    }
    public Set<Student>getStudents() {
       returnstudents;
    }
    publicvoidsetStudents(Set<Student> students) {
       this.students = students;
    }
}

publicclass Student {
    private Integer id;
    private String name;
    private Integer age;
    public Integer getId() {
       returnid;
    }
    publicvoid setId(Integerid) {
        this.id = id;
    }
    public String getName() {
       returnname;
    }
    publicvoid setName(Stringname) {
       this.name = name;
    }
    public Integer getAge() {
       returnage;
    }
    publicvoid setAge(Integerage) {
       this.age = age;
    }
}

<?
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 package="csg.hibernate.entity">
    <class name="Teacher" table="t_teacher">
       <id name="id">
           <column name="id"/>
           <generator class="native" />
       </id>
       <property name="name" />
       <set name="students" table="t_s_two"><!—-自己定义表名-->
           <key column="teacher_id"/><!—自己定义列名-->
           <many-to-many class="csg.hibernate.entity.Student" column="student_id"/><!—自己定义列名-->
       </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 package="csg.hibernate.entity">
    <class name="Student" table="t_student">
       <id name="id">
           <column name="id"/>
           <generator class="native" />
       </id>
       <property name="name" />
       <property name="age" />
    </class>
</hibernate-mapping>


以上就是XML的many-to-many(单向)的配置方法，ok！