java之mybatis之一對多關聯映射

1.在一對多的關聯映射中，表結構如下

2.實體類結構

User.java

public class User implements Serializable{
    private int id;
    private String name;
    private int age;
    private int roleId;
    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;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public int getRoleId() {
        return roleId;
    }
    public void setRoleId(int roleId) {
        this.roleId = roleId;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + ", roleId=" + roleId +  "]";
    }
}

Role.java

public class Role {
    private int id;
    private String name;
    private List<User> users; 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;
    }
    public List<User> getUsers() {
        return users;
    }
    public void setUsers(List<User> users) {
        this.users = users;
    }
    @Override
    public String toString() {
        return "Role [id=" + id + ", name=" + name + "]";
    }
}

3.映射文件

<mapper namespace="cn.sxt.vo.RoleMapper">
    <select id="findById" resultMap="RoleMap">
        select u.id as uid,u.name as uname,u.age as uage,
        roleId,r.name as rname from t_user u,t_role r 
        where u.roleId=r.id and r.id=#{id} </select>
    <resultMap type="Role" id="RoleMap">
        <id property="id" column="roleId"/>
        <result property="name" column="rname"/>
        <collection property="users" ofType="User">
            <id property="id" column="uid"/>
            <result property="name" column="uname"/>
            <result property="age" column="uage"/>
            <result property="roleId" column="roleId"/>
        </collection>
    </resultMap>
</mapper>

4.測試

　　@Test
    public void testFindById() throws IOException{
        SqlSession session = MybatisUtil.getSqlSession();
        Role role = (Role)session.selectOne("cn.sxt.vo.RoleMapper.findById",2);
        System.out.println(role.getId()+"-----"+role.getName());
        for(User u:role.getUsers()){
            System.out.println(u);
        }
        session.close();
    }

5.使用2個映射語句實現映射

RoleMapper.xml

<select id="findById" resultMap="RoleMap">
        select * from t_role where id=#{id}
    </select>
    <resultMap type="Role" id="RoleMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <!-- javaType指property的類型 不要忘了寫column-->
        <collection property="users" column="id" javaType="list"
        ofType="User" select="cn.sxt.vo.UserMapper.findUserByRoleId"
        ></collection>
    </resultMap>

UserMapper.xml

<mapper namespace="cn.sxt.vo.UserMapper">
    <select id="findUserByRoleId" resultType="User">
        select * from t_user where roleId=#{roleId}
    </select>
</mapper>