public interface ClazzMapper {

    /**
     * 分布查詢第二步
     * 根據(jù)cid獲取Clazz信息
     * @param cid
     * @return
     */
    Clazz selectByCid(Integer cid);
}

<?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="mapper.ClazzMapper">
<select id="selectByCid" resultType="Clazz">
    select cid,cname from t_clazz where cid = #{cid}
</select>
</mapper>

  <resultMap id="studentResultMapByStep" type="Student">
        <id property="sid" column="sid"/>
        <id property="sname" column="sname"/>
       <association property="clazz"
                            select="mapper.ClazzMapper.selectByCid"
                            column="cid"
                            fetchType="lazy"/> <!--添加延遲-->
    </resultMap>

<!--兩條sql語(yǔ)句，完成多對(duì)一的分布查詢-->
<!--    這是第一步，根據(jù)id值查詢學(xué)生的所有信息，這些信息當(dāng)中含有班級(jí)id(cid-->
<select id="selectByIdStep1" resultMap="studentResultMapByStep" >
    select sid,sname,cid from t_student_plus where sid = #{sid}
</select>

package pojo;

import java.util.List;

/**
 * 班級(jí)信息
 */
public class Clazz {

    public Clazz() {
    }

    private Integer cid;
    private String cname;
    private List<Student> stus;

    public List<Student> getStus() {
        return stus;
    }

    @Override
    public String toString() {
        return "Clazz{" +
                "cid=" + cid +
                ", cname='" + cname + '\'' +
                ", stus=" + stus +
                '}';
    }

    public void setStus(List<Student> stus) {
        this.stus = stus;
    }

    public Integer getCid() {
        return cid;
    }

    public void setCid(Integer cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public Clazz(Integer cid, String cname) {
        this.cid = cid;
        this.cname = cname;
    }
}

public interface ClazzMapper {

    /**
     * 根據(jù)cid獲取Clazz信息
     * @param cid
     * @return
     */
    Clazz selectByCid(Integer cid);

    /**
     * 根據(jù)班級(jí)編號(hào)查詢班級(jí)信息。同時(shí)班級(jí)中所有的學(xué)生信息也要查詢。
     * @param cid
     * @return
     */
    Clazz selectClazzAndStusByCid(Integer cid);
}

<resultMap id="clazzResultMap" type="Clazz">
  <id property="cid" column="cid"/>
  <result property="cname" column="cname"/>
  <collection property="stus" ofType="Student">
    <id property="sid" column="sid"/>
    <result property="sname" column="sname"/>
  </collection>
</resultMap>

<select id="selectClazzAndStusByCid" resultMap="clazzResultMap">
  select * from t_clazz c join t_student s on c.cid = s.cid where c.cid = #{cid}
</select>

<resultMap id="clazzResultMap" type="Clazz">
  <id property="cid" column="cid"/>
  <result property="cname" column="cname"/>
  <!--主要看這里-->
  <collection property="stus"
              select="com.powernode.mybatis.mapper.StudentMapper.selectByCid"
              column="cid"/>
</resultMap>

<!--sql語(yǔ)句也變化了-->
<select id="selectClazzAndStusByCid" resultMap="clazzResultMap">
  select * from t_clazz c where c.cid = #{cid}
</select>

/**
* 根據(jù)班級(jí)編號(hào)獲取所有的學(xué)生。
* @param cid
* @return
*/
List<Student> selectByCid(Integer cid);

<select id="selectByCid" resultType="Student">
  select * from t_student where cid = #{cid}
</select>