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本文将阐述mybatis中的表在一对多关系的情况下完成查询操作。

1、环境约束

• win10 64位操作系统
• idea2018.1.5
• jdk-8u162-windows-x64
• mybatis3.2.8
• mysql 6.5

2、前提约束

• 完成mybatis的延迟加载

3、操作

• 创建一个班级表、学生表以及插入数据

create table t_class(id int, name varchar(20));insert into t_class(id,name) values(1,'java132');insert into t_class(id,name) values(2,'java133');create table t_stu(id int, name varchar(20),classid int);insert into t_stu(id,name,classid) values(1,'ali',1);insert into t_stu(id,name,classid) values(2,'zhangli',1);insert into t_stu(id,name,classid) values(3,'xiaoli',2);insert into t_stu(id,name,classid) values(4,'erli',2);

• 加入两张表的实体类
  Clazz.java

package net.wanho.entity;import java.io.Serializable;import java.util.List;public class Clazz implements Serializable {    private int id;    private String name;    private List
   
     students;    public Clazz(int id, String name) {        this.id = id;        this.name = name;    }    public Clazz() {    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public List
    
      getStudents() {        return students;    }    public void setStudents(List
     
       students) {        this.students = students;    }}
     
    
   

Student.java

package net.wanho.entity;import java.io.Serializable;public class Student implements Serializable {    private int id;    private String name;    private int classid;    public Student(int id, String name, int classid) {        this.id = id;        this.name = name;        this.classid = classid;    }    public Student() {    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getClassid() {        return classid;    }    public void setClassid(int classid) {        this.classid = classid;    }}

• 在UserMapper.java中加入方法声明

• 在UserMapper.xml中加入标签

        select * from t_class                select * from t_student where classid=#{id}         
           
            
            
            
            
        
       
           
            
        
   

• 测试

//关键代码String resource ="mybatis-config.xml";Reader reader = Resources.getResourceAsReader(resource);SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(reader);SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper userMapper = sqlSession.getMapper(UserMapper.class);List
   
     clazzList = userMapper.queryClazz();System.out.println(clazzList);
   

以上就是mybatis中一对多查询的过程。

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