Mybatis一对多关联查询详解

要点

在Student类中添加List

classList 属性

在Classes类中添加List

students属性

在ClassesMapper.xml中

1.创建数据表

classes表

2.创建实体类

Student：

package com.ytsky.mybatis.demo.entity; import java.util.List; public class Student { private int id; private String stuno; private String stuname; private String sex; private String classno; private List 
   
     classesList; public int getId() { return id; } public void setId(int id) { this.id = id; } public List 
    
      getClassesList() { return classesList; } public void setClassesList(List 
     
       classesList) { this.classesList = classesList; } public String getStuno() { return stuno; } public void setStuno(String stuno) { this.stuno = stuno; } public String getStuname() { return stuname; } public void setStuname(String stuname) { this.stuname = stuname; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public String getClassno() { return classno; } public void setClassno(String classno) { this.classno = classno; } @Override public String toString() { return "Student{" + "id=" + id + ", stuno='" + stuno + '\'' + ", stuname='" + stuname + '\'' + ", sex='" + sex + '\'' + ", classno='" + classno + '\'' + ", classesList=" + classesList + '}'; } } 
      
     
   

Classes：

package com.ytsky.mybatis.demo.entity; import java.util.List; public class Classes { private int id; private String classno; private String name; private String major; private List 
   
     students; public List 
    
      getStudents() { return students; } public void setStudents(List 
     
       students) { this.students = students; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getClassno() { return classno; } public void setClassno(String classno) { this.classno = classno; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getMajor() { return major; } public void setMajor(String major) { this.major = major; } @Override public String toString() { return "Classes{" + "id=" + id + ", classno='" + classno + '\'' + ", name='" + name + '\'' + ", major='" + major + '\'' + ", students=" + students + '}'; } } 
      
     
   

3.创建映射文件 

 ClassesMapper.xml

 
    
    
     select classes.id, classes.classno, name, major ,student.id, student.classno, stuno, sex, stuname from db_quote.classes join db_quote.student on db_quote.student.id = db_quote.classes.id where db_quote.student.classno="Class001";  
     
      
      
      
      
      
       
       
       
       
      
     
    

StudentMapper.xml

 
    
    
     select student.id, stuno, stuname, sex, student.classno ,classes.id, classes.classno,name, major from db_quote.student join db_quote.classes on classes.id = student.id;  
     
      
      
      
      
      
      
       
       
       
       
      
     
    

mybatis-config.xml

4.创建数据操作接口

ClassesMapper:

package com.ytsky.mybatis.demo.dao; import com.ytsky.mybatis.demo.entity.Classes; import java.util.List; public interface ClassesMapper { List 
   
     selectClassesWithStudent(); } 
   

StudentMapper:

package com.ytsky.mybatis.demo.dao; import com.ytsky.mybatis.demo.entity.Student; import java.util.List; public interface StudentMapper { List 
   
     selectStudentWithClasses(); int updateById(Student student); } 
   

5.编写测试类

Test1：

package com.ytsky.mybatis.demo.test1; import com.ytsky.mybatis.demo.dao.ClassesMapper; import com.ytsky.mybatis.demo.dao.StudentMapper; import com.ytsky.mybatis.demo.entity.Classes; import com.ytsky.mybatis.demo.entity.Student; 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 java.io.IOException; import java.util.List; public class Test1 { private static SqlSessionFactory factory; static { try{ factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml")); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) { // System.out.println(findClassesWithStudent()); System.out.println(findStudentWithClasses()); } public static List 
   
     findClassesWithStudent(){ SqlSession session = factory.openSession(); List 
    
      classes = session.getMapper(ClassesMapper.class).selectClassesWithStudent(); session.close(); return classes; } public static List 
     
       findStudentWithClasses(){ SqlSession session = factory.openSession(); List 
      
        students = session.getMapper(StudentMapper.class).selectStudentWithClasses(); session.close(); return students ; } } 
       
      
     
   

6.运行结果