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

Question

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();
        }









}

Answer 1

## # 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=#{sId,jdbcType=INTEGER}

</collection> 

select st_id stId, st_class stClass, st_name stName,st_dream stDream

from student s where s.st_s=#{sId,jdbcType=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](https://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();
        }