mybatis高级映射——(一对多查询)

1.当一对多查询时可能会出现如下情况

select students.*,admin.a_id,admin.a_username,admin.a_password,evaluate.e_sudent_t from 
students,admin,evaluate where students.s_studentid=admin.a_nameid 
and evaluate.e_studentid = students.s_studentid;

2.编码实现

要不能出现重复学生信息

在StudentBean.java中添加属性，List evaluateBeans 。

package mybatis.ma.entity;

import java.util.List;

/**
 * Created by 马欢欢 on 2017/6/6.
 */
public class StudentBean {
    private int s_id;
    private String  s_studentid;
    private String s_username;
    private String s_password;
    private String s_sex;
    private String s_class;
    private String s_rank;

    private List evaluateBeans;



    public List getEvaluateBeans() {
        return evaluateBeans;
    }

    public void setEvaluateBeans(List evaluateBeans) {
        this.evaluateBeans = evaluateBeans;
    }

    public int getS_id() {
        return s_id;
    }

    public void setS_id(int s_id) {
        this.s_id = s_id;
    }

    public String getS_studentid() {
        return s_studentid;
    }

    public void setS_studentid(String s_studentid) {
        this.s_studentid = s_studentid;
    }

    public String getS_username() {
        return s_username;
    }

    public void setS_username(String s_username) {
        this.s_username = s_username;
    }

    public String getS_password() {
        return s_password;
    }

    public void setS_password(String s_password) {
        this.s_password = s_password;
    }

    public String getS_sex() {
        return s_sex;
    }

    public void setS_sex(String s_sex) {
        this.s_sex = s_sex;
    }

    public String getS_class() {
        return s_class;
    }

    public void setS_class(String s_class) {
        this.s_class = s_class;
    }

    public String getS_rank() {
        return s_rank;
    }

    public void setS_rank(String s_rank) {
        this.s_rank = s_rank;
    }
    @Override
    public String toString() {
        return "StudentBean{" +
                "s_id=" + s_id +
                ", s_studentid='" + s_studentid + '\'' +
                ", s_username='" + s_username + '\'' +
                ", s_password='" + s_password + '\'' +
                ", s_sex='" + s_sex + '\'' +
                ", s_class='" + s_class + '\'' +
                ", s_rank='" + s_rank + '\'' +
                ", evaluateBeans=" + evaluateBeans +
                '}';
    }
}

mapper.xml (StudentEvaluateMapper.xml)

    
        
        
        
        
        
        
        
        
        
            
            
            
        
    

    
        select students.*,evaluate.e_sudent_t ,evaluate.e_time from students,admin,evaluate
                where students.s_studentid=admin.a_nameid and
                     evaluate.e_studentid = students.s_studentid;
    

接口：StudentEvaluateMapper.java

package mybatis.ma.mapper;

import mybatis.ma.entity.StudentBean;

import java.util.List;

/**
 * Created by 马欢欢  on 17-7-1.
 */
public interface StudentEvaluateMapper {

    List findStudentEvaluateInfo() throws Exception;
}

配置文件：mybatis-config.xml

测试：StudentEvaluateMapperTest.java

package mybatis.ma.mybatisTest;



import mybatis.ma.entity.StudentBean;
import mybatis.ma.mapper.StudentEvaluateMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

/**
 * Created by 马欢欢  on 17-7-1.
 */
public class StudentEvaluateMapperTest {
    private SqlSessionFactory sqlSessionFactory;
    @Before
    //测试前执行
    public void setUp() throws IOException {
        //配置文件
        String resource = "mybatis-config.xml";
        //的到配置文件流
        InputStream inputStream =  Resources.getResourceAsStream(resource);
        //创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void findStudentEvaluateInfo() throws Exception{
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //StudentCustomMapper，mybatis自动生成mapper代理对象
        StudentEvaluateMapper studentEvaluateMapper = sqlSession.getMapper(StudentEvaluateMapper.class);
        List studentBeans = studentEvaluateMapper.findStudentEvaluateInfo();
        System.out.println(studentBeans);
        sqlSession.close();

    }
}

总结：mybatis使用resultMap实现一对多查询用collection对关联查询出的多条记录映射到一个list集合中

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