问题描述

MyBatis使用select关联 一对多表的时候？？？？？？？？？？？？？

SchoolMapper.xml 关联关系是一个学校里面有很多学生

student 表的属性如下:

school表如下：

school.xml如下:

public class School {

//建立一对多的关系private List<Student> slist;public List<Student> getSlist() {    return slist;}public void setSlist(List<Student> slist) {    this.slist = slist;}private Integer sId;private String sName;private String sAddress;public Integer getsId() {    return sId;}public void setsId(Integer sId) {    this.sId = sId;}public String getsName() {    return sName;}public void setsName(String sName) {    this.sName = sName == null ? null : sName.trim();}public String getsAddress() {    return sAddress;}public void setsAddress(String sAddress) {    this.sAddress = sAddress == null ? null : sAddress.trim();}

public class Student {
//建立多多对一的关系

private School school;public School getSchool() {    return school;}public void setSchool(School school) {    this.school = school;}private Integer stId;private String stClass;private String stName;private String stDream;private Integer stS;public Integer getStId() {    return stId;}public void setStId(Integer stId) {    this.stId = stId;}public String getStClass() {    return stClass;}public void setStClass(String stClass) {    this.stClass = stClass == null ? null : stClass.trim();}public String getStName() {    return stName;}public void setStName(String stName) {    this.stName = stName == null ? null : stName.trim();}public String getStDream() {    return stDream;}public void setStDream(String stDream) {    this.stDream = stDream == null ? null : stDream.trim();}public Integer getStS() {    return stS;}public void setStS(Integer stS) {    this.stS = stS;}test.java  结果list就是null  public static void main(String[] args) {    // TODO Auto-generated method stub    StuService ss=new StuService();    ss.selectSchool();}public void selectSchool(){      SqlSession ss=null;        try {            ss=sf.openSession();                                                         //selectByPrimaryKey        School sc =ss.selectOne(""com.wuye.dao.SchoolMapper.selectSchool"" 1);        System.out.println(""学校的信息:""+sc.getsId()+"" ""+sc.getsName()+"" ""+sc.getsAddress());    List<Student> lis=sc.getSlist();    for(Student st:lis){        System.out.println(""学生信息学号:""+st.getStId()+""名字:""+st.getStName()+""所在班级: ""+st.getStClass()+""梦想:""+st.getStDream()+""所在学校编号:==""+st.getStS());    }        } catch (Exception e) {        // TODO: handle exception          e.printStackTrace();        }}

解决方案

是这样的啊，定义自己定义resultMap指定类的属性和查询列的映射关系，集合列指定select语句。
你这段代码怎么了，有报错么？

解决方案二：
## # 上面肯写的不清楚：

SchoolMapper.xml 关联关系是一个学校里面有很多学生

 <select id=""selectSchool"" resultMap=""BaseResultMap3""  parameterType=""java.lang.Integer"">

select * from school sc where sc.s_id=#{sIdjdbcType=INTEGER}

</collection> 

select st_id stId st_class stClass st_name stNamest_dream stDream

from student s where s.st_s=#{sIdjdbcType=INTEGER}

StudentMapper.xml<mapper namespace=""com.wuye.dao.StudentMapper"" >

<association property=""school"" column=""st_s"" select=""selectShoolByStu"" ></association>

两个表：!![图片说明](http://img.ask.csdn.net/upload/201604/04/1459759020_969759.png)

public class School {

//建立一对多的关系private List<Student> slist;public List<Student> getSlist() {    return slist;}public void setSlist(List<Student> slist) {    this.slist = slist;}private Integer sId;private String sName;private String sAddress;public Integer getsId() {    return sId;}public void setsId(Integer sId) {    this.sId = sId;}public String getsName() {    return sName;}public void setsName(String sName) {    this.sName = sName == null ? null : sName.trim();}public String getsAddress() {    return sAddress;}public void setsAddress(String sAddress) {    this.sAddress = sAddress == null ? null : sAddress.trim();}

public class Student {
//建立多多对一的关系

private School school;public School getSchool() {    return school;}public void setSchool(School school) {    this.school = school;}private Integer stId;private String stClass;private String stName;private String stDream;private Integer stS;public Integer getStId() {    return stId;}public void setStId(Integer stId) {    this.stId = stId;}public String getStClass() {    return stClass;}public void setStClass(String stClass) {    this.stClass = stClass == null ? null : stClass.trim();}public String getStName() {    return stName;}public void setStName(String stName) {    this.stName = stName == null ? null : stName.trim();}public String getStDream() {    return stDream;}public void setStDream(String stDream) {    this.stDream = stDream == null ? null : stDream.trim();}public Integer getStS() {    return stS;}public void setStS(Integer stS) {    this.stS = stS;}test.java  结果list就是null  public static void main(String[] args) {    // TODO Auto-generated method stub    StuService ss=new StuService();    ss.selectSchool();}public void selectSchool(){      SqlSession ss=null;        try {            ss=sf.openSession();                                                         //selectByPrimaryKey        School sc =ss.selectOne(""com.wuye.dao.SchoolMapper.selectSchool"" 1);        System.out.println(""学校的信息:""+sc.getsId()+"" ""+sc.getsName()+"" ""+sc.getsAddress());    List<Student> lis=sc.getSlist();    for(Student st:lis){        System.out.println(""学生信息学号:""+st.getStId()+""名字:""+st.getStName()+""所在班级: ""+st.getStClass()+""梦想:""+st.getStDream()+""所在学校编号:==""+st.getStS());    }        } catch (Exception e) {        // TODO: handle exception          e.printStackTrace();        }