双向多对多

Posted 2020-08-06 -EASY-

1.在双方实体类里添加对方的集合

Emp实体类：

public class Emp {
    private Integer nid;
    private String empname;
    Set<Project> pros=new HashSet<Project>();
    
    
    public Emp() {
        super();
    }
    public Emp(Integer nid, String empname) {
        super();
        this.nid = nid;
        this.empname = empname;
    }
    public Integer getNid() {
        return nid;
    }
    public void setNid(Integer nid) {
        this.nid = nid;
    }
    public String getEmpname() {
        return empname;
    }
    public void setEmpname(String empname) {
        this.empname = empname;
    }
    public Set<Project> getPros() {
        return pros;
    }
    public void setPros(Set<Project> pros) {
        this.pros = pros;
    }
}

Project实体类：

public class Project {
    private int pid;
    private String pname;
    private Set<Emp> emps=new HashSet<Emp>();
    
    
    public Project() {
        super();
    }
    public Project(int pid, String pname) {
        super();
        this.pid = pid;
        this.pname = pname;
    }
    public Set<Emp> getEmps() {
        return emps;
    }
    public void setEmps(Set<Emp> emps) {
        this.emps = emps;
    }
    public int getPid() {
        return pid;
    }
    public void setPid(int pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    
}

2.双向的多对多需要在双方的小配置里添加<set></set>元素  *需要加table属性*:

Emp.hbm.xml

<?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="cn.a.happy">
     <class name="Emp" table="EMP">
        <id name="nid" column="nid">
        <!-- native   数据库方言的可移植性 -->
           <generator class="native"></generator>
        </id>
        <property name="empname" type="string" column="empname"/>
        
        <!-- 多对多 -->
        <set name="pros" table="ProEmp" >
            <key column="nid"/>    <!-- 在哪个配置，就写配置对应的主键 -->
            <many-to-many class="Project" column="pid"/>    <!-- 对应多的一方成员类型 -->
        </set>
    </class>
</hibernate-mapping>

Project.hbm.xml：

<?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="cn.a.happy">
     <class name="Project" table="PROJECT">
        <id name="pid" column="pid">
           <generator class="native"></generator>
        </id>
        <property name="pname" type="string" column="pname"/>
         <!-- 多对多 
               需要在<set>元素里 加一个table属性
               table="生成第三张表的名字"
         -->
        <set name="emps" table="ProEmp" >
            <key column="pid"/>    <!-- 在哪个配置，就写配置对应的主键 -->
            <many-to-many class="Emp" column="nid"/>    <!-- 对应多的一方成员类型 -->
        </set>
        
    </class>
</hibernate-mapping>

进行测试：

/**
         * 多对多双向关联测试
         * 添加操作
         */
        @Test
        public void muchVsMuchTest(){
            Emp emp1=new Emp(1,"李睿智");
            Emp emp2=new Emp(2,"小明");
            
            
            Project project1=new Project(1,"一号项目");
            Project project2=new Project(2,"二号项目");
            
            project1.getEmps().add(emp1);
            project1.getEmps().add(emp2);
            
            project2.getEmps().add(emp1);
            
            session.save(project1);
            session.save(project2);
        }