Mybatis XML映射文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper  PUBLIC "-//mybatis.org//DTD mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.bean.userMapper">
    <select id="getUser" parameterType="int"  resultType="com.mybatis.bean.User">
        select * from users where id=#{id}
    </select>

    <insert id="insertUser" parameterType="com.mybatis.bean.User">
        insert into users(name,age) values(#{name},#{age});
    </insert>

    <update id="updateUser" parameterType="com.mybatis.bean.User">
       update  users set name=#{name} ,age=#{age} where id=#{id}
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from users where id=#{id}
    </delete>

    <select id="allUser" resultType="com.mybatis.bean.User">
        select * from users
    </select>
</mapper>

public class User {

    private int id;
    private String name;
    private int age;

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }
 
}

public class Classes {
  
    private int id;
    private String name;
    private Teacher teacher; 
    // 省略
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.bean.ClassMapper">
    <select id="getClass" parameterType="int" resultMap="ClassResultMap">
       select * from class c,teacher t where c.teacher_id = t.t_id and c.c_id=#{id}
    </select>

    <resultMap id="ClassResultMap" type="classes">
     <id property="id" column="c_id"/>
     <result property="name" column="c_name"/>
     <association property="teacher" column="teacher_id" javaType="teacher">
           <id property="id" column="t_id"/>
           <result property="name" column="t_name"/>
     </association>
    </resultMap>
    
</mapper>

<collection property="posts" ofType="domain.blog.Post">
  <id property="id" column="post_id"/>
  <result property="subject" column="post_subject"/>
  <result property="body" column="post_body"/>
</collection>