1、什么是MyBatis?

MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。

iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAO）。

MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs（Plain Ordinary Java Objects，普通的 Java对象）映射成数据库中的记录。

2、MyBatis 入门实例基于xml配置

①、创建MySQL数据库：mybatisDemo和表：person

create database mybatisDemo;use mybatisDemo;create table person(pid int primary key AUTO_INCREMENT, pname varchar(50), page int);

②、建立一个Java工程，并导入相应的jar包

③、在 MyBatisDemo 工程中添加数据库配置文件 mybatis-configuration.xml

④、定义表所对应的实体类

package com.ys.bean; public class Person {    private int pid;    private String pname;    private int page;         public int getPid() {        return pid;    }    public void setPid(int pid) {        this.pid = pid;    }    public String getPname() {        return pname;    }    public void setPname(String pname) {        this.pname = pname;    }    public int getPage() {        return page;    }    public void setPage(int page) {        this.page = page;    }    @Override    public String toString() {        return "Person [pid=" + pid + ", pname=" + pname + ", page=" + page                + "]";    }}

⑤、定义操作 person 表的sql映射文件personMapper.xml

    
      
       
         
          select * from person where pid = #{pid}       
       
         select * from person       
       
     
          update person set pname=#{pname},page=#{page} where pid = #{pid}  
          
       
     
          insert into person(pid,pname,page) values(#{pid},#{pname},#{page})  
          
       
     
          delete from person where pid=#{pid}  
        
    

⑥、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件

⑦、创建测试类

package com.ys.test; import java.io.InputStream;import java.util.List; 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 com.ys.bean.Person; public class MyBatisTest {    SqlSession session;         @Before    public void beforeLoadXML(){        //加载 mybatis 配置文件        InputStream inputStream = MyBatisTest.class.                getClassLoader().getResourceAsStream("mybatis-configuration.xml");        //构建sqlSession的工厂        SqlSessionFactory sqlSessionFactory =                new SqlSessionFactoryBuilder().build(inputStream);        //根据 sqlSessionFactory 产生 session        session = sqlSessionFactory.openSession();    }         //根据 pid 查询 person 表中的数据    @Test    public void testSelectById(){        //这个字符串有 personMapper.xml 文件中 两个部分构成        //
    
      的 namespace 的值        //
      id 值        String statement = "com.ys.bean.personMapper"+".selectPersonById";        Person p = session.selectOne(statement, 1);        System.out.println(p);        session.close();    }         //查询person 表所有数据    @Test    public void testGetAllPerson(){        String statement = "com.ys.bean.personMapper.getAllPerson";        List listPerson = session.selectList(statement);        System.out.println(listPerson);        session.close();    }         //根据id更新数据    @Test    public void updateById(){        String statement = "com.ys.bean.personMapper.updatePersonById";        Person p = new Person();        p.setPid(1);        p.setPname("aaa");        p.setPage(11);        session.update(statement, p);        session.commit();        session.close();    }         //向 person 表插入一条数据    @Test    public void addPerson(){        String statement = "com.ys.bean.personMapper.addPerson";        Person p = new Person();        //由于我们设置了主键的自增长机制，故这里不需要手动设置 pid 的值        //p.setPid(1);        p.setPname("add");        p.setPage(11);        session.insert(statement, p);        session.commit();        session.close();    }         //根据 pid 删除person 表中的数据    @Test    public void deletePersonById(){        String statement = "com.ys.bean.personMapper.deletePersonById";        session.delete(statement, 1);        session.commit();        session.close();             }}
    

3、MyBatis 入门实例注解配置

①、上面的前面四步都是一样的，但是第五步不一样，我们不需要创建 personMapper.xml 文件，首先在 src 目录下创建 personMapper.java 文件

package com.ys.annocation; import org.apache.ibatis.annotations.Delete;import org.apache.ibatis.annotations.Insert;import org.apache.ibatis.annotations.Select;import org.apache.ibatis.annotations.Update; import com.ys.bean.Person; public interface PersonMapper {         @Insert("insert into person(pid,pname,page) values(#{pid},#{pname},#{page})")    public int add(Person person);         @Select("select * from person where pid = #{pid}")    public Person getPerson(int pid);         @Update("update person set pname=#{pname},page=#{page} where pid = #{pid}")    public int updatePerson(Person preson);         @Delete("delete from person where pid=#{pid}")    public int deletePerson(int pid); }

②、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件

③、编写测试类

@Testpublic void testAnnocation(){    PersonMapper mapper = session.getMapper(PersonMapper.class);    Person p = new Person();    p.setPid(7);    p.setPname("abc");    p.setPage(11);    //调用增加方法    mapper.add(p);    //调用查询方法    Person p1 = mapper.getPerson(3);    System.out.println(p1);    //调用更新方法    p.setPage(100);    mapper.updatePerson(p);    //调用删除方法    mapper.deletePerson(7);    session.commit();    session.close();}

4、MyBatis 入门实例 一对一 基于xml配置

这里我们以老师和班级为例，假设一般班级只能拥有有一个老师，一个老师只能带一个班级。

①、创建实体类

Teacher.java

package one.to.one;

public class Teacher {

private int tid;

private String tname;

private Classes classes;

public int getTid() {    return tid;}public void setTid(int tid) {    this.tid = tid;}public String getTname() {    return tname;}public void setTname(String tname) {    this.tname = tname;}public Classes getClasses() {    return classes;}public void setClasses(Classes classes) {    this.classes = classes;}@Overridepublic String toString() {    return "Teacher [tid=" + tid + ", tname=" + tname + ", classes=" + classes + "]";}

}

Classes.java

package one.to.one; public class Classes {    private int cid;    private String cname;    private Teacher teacher;         public int getCid() {        return cid;    }    public void setCid(int cid) {        this.cid = cid;    }    public String getCname() {        return cname;    }    public void setCname(String cname) {        this.cname = cname;    }    public Teacher getTeacher() {        return teacher;    }    public void setTeacher(Teacher teacher) {        this.teacher = teacher;    }    @Override    public String toString() {        return "Classes [cid=" + cid + ", cname=" + cname + ", teacher=" + teacher + "]";    }     }

②、在数据库中根据实体类创建相应的数据表

③、定义操作 Classes 表的sql映射文件classesMapper.xml　

    
        
         
             select * from classes c ,teacher t            where c.tid=t.tid and c.tid=#{tid}        
             
              
              
                  
                   
               
          
         
         
             select * from teacher t,classes c            where t.cid = c.cid and t.cid=#{cid}        
             
              
              
                  
                   
               
          
                   
               
         
             select * from classes c where c.cid = #{cid}        
             
              
              
              
          
         
             select tid tid,tname tname from teacher where tid=#{tid}       
    

　说明：我们这里一对一的关联操作，有两种方式：

　　　　1、使用嵌套结果映射来处理重复的联合结果的子集

　　　　2、通过执行另外一个SQL映射语句来返回预期的复杂类型

　　　　相关属性解释：

④、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 文件

⑤、编写测试类

package one.to.one; import java.io.InputStream; 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 com.ys.test.MyBatisTest; public class OneToOneTest {SqlSession session;         @Before    public void beforeLoadXML(){        //加载 mybatis 配置文件        InputStream inputStream = MyBatisTest.class.                getClassLoader().getResourceAsStream("mybatis-configuration.xml");        //构建sqlSession的工厂        SqlSessionFactory sqlSessionFactory =                new SqlSessionFactoryBuilder().build(inputStream);        //根据 sqlSessionFactory 产生 session        session = sqlSessionFactory.openSession();    }         //一对一嵌套结果方式：根据教师id查询班级信息    @Test    public void testGetClasses(){        String statement = "one.to.one.classesMapper.getClasses";        Classes c = session.selectOne(statement, 1);        System.out.println(c);    }         //一对一嵌套结果方式：根据班级id查询教师信息    @Test    public void testGetTeacher(){        String statement = "one.to.one.classesMapper.getTeacher";        Teacher t = session.selectOne(statement, 1);        System.out.println(t);    }         //一对一嵌套查询方式：根据教师id查询班级信息    @Test    public void testGetClasses2(){        String statement = "one.to.one.classesMapper.getClasses2";        Classes c = session.selectOne(statement, 1);        System.out.println(c);    }           }

4、MyBatis 入门实例 一对多，多对一 基于xml配置

这里我们以班级和学生为例，一个班级里面对应多个学生，这是一对多；反过来，多个学生对应一个班级，这是多对一

①、建立学生和班级的实体类

Student.java

package one.to.many; public class Student {    private int sid;    private String sname;    private Classes classes;    public int getSid() {        return sid;    }    public void setSid(int sid) {        this.sid = sid;    }    public String getSname() {        return sname;    }    public void setSname(String sname) {        this.sname = sname;    }    public Classes getClasses() {        return classes;    }    public void setClasses(Classes classes) {        this.classes = classes;    }    @Override    public String toString() {        return "Student [sid=" + sid + ", sname=" + sname + ", classes=" + classes + "]";    }     }

Classes.java

package one.to.many; import java.util.Set; public class Classes {    private int cid;    private String cname;    private Set
    
      students;         public int getCid() {        return cid;    }    public void setCid(int cid) {        this.cid = cid;    }    public String getCname() {        return cname;    }    public void setCname(String cname) {        this.cname = cname;    }    public Set
     
       getStudents() {        return students;    }    public void setStudents(Set
      
        students) {        this.students = students;    }    @Override    public String toString() {        return "Classes [cid=" + cid + ", cname=" + cname + ", students=" + students + "]";    }}
      
     
    

②、在数据库中根据实体类创建相应的数据表

③、多对一：定义操作 Classes 表的sql映射文件classesMapper.xml

    
        
             select * from classes c,student s where s.cid=c.cid and c.cid=#{cid}        
             
              
              
                  
                   
               
          
          
    

④、一对多：定义操作 Student 表的sql映射文件studentMapper.xml

    
        
             select * from classes c,student s where s.cid=c.cid and s.sid=#{sid}        
             
              
              
                  
                   
               
          
          
    

⑤、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 、studentMapper.xml文件

⑥、编写测试类

package one.to.many; import java.io.InputStream; 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 com.ys.test.MyBatisTest; public class OneToManyTest {SqlSession session;         @Before    public void beforeLoadXML(){        //加载 mybatis 配置文件        InputStream inputStream = MyBatisTest.class.                getClassLoader().getResourceAsStream("mybatis-configuration.xml");        //构建sqlSession的工厂        SqlSessionFactory sqlSessionFactory =                new SqlSessionFactoryBuilder().build(inputStream);        //根据 sqlSessionFactory 产生 session        session = sqlSessionFactory.openSession();    }         //一对多嵌套结果方式：根据班级id查询班级所有的学生信息    @Test    public void testGetClasses(){        String statement = "one.to.many.classesMapper.getClasses";        Classes c = session.selectOne(statement, 1);        System.out.println(c);        System.out.println(c.getStudents().size());    }              //多对一嵌套结果方式：根据学生id查询班级信息    @Test    public void testGetStudents(){        String statement = "many.to.one.studentMapper.getStudents";        Student s = session.selectOne(statement, 1);        System.out.println(s);        System.out.println(s.getClasses());    }}

5、MyBatis 入门实例 多对多 基于xml配置

这里我们以 users 表和 groups 表为例，一个 users 可能加入多个 groups，而一个 groups 可能包含多个 users，故构成 多对多 的关联

①、在数据库中建立相应的表

users 表

groups 表

两者之间的关联表users_groups表

②、建立对应的实体类

Users.java

package many.to.many; import java.util.Set; public class Users {    private int uid;    private String uname;    private Set
    
      groups;    public int getUid() {        return uid;    }    public void setUid(int uid) {        this.uid = uid;    }    public String getUname() {        return uname;    }    public void setUname(String uname) {        this.uname = uname;    }    public Set
     
       getGroups() {        return groups;    }    public void setGroups(Set
      
        groups) {        this.groups = groups;    }    @Override    public String toString() {        return "User [uid=" + uid + ", uname=" + uname + ", groups=" + groups + "]";    }     }
      
     
    

Groups.java

package many.to.many; import java.util.Set; public class Groups {    private int gid;    private String gname;    private Set
    
      users;    public int getGid() {        return gid;    }    public void setGid(int gid) {        this.gid = gid;    }    public String getGname() {        return gname;    }    public void setGname(String gname) {        this.gname = gname;    }    public Set
     
       getUsers() {        return users;    }    public void setUsers(Set
      
        users) {        this.users = users;    }    @Override    public String toString() {        return "Group [gid=" + gid + ", gname=" + gname + ", users=" + users + "]";    }     }
      
     
    

Users_Groups.java

package many.to.many; public class Users_Groups {    private Users user;    private Groups group;    public Users getUser() {        return user;    }    public void setUser(Users user) {        this.user = user;    }    public Groups getGroup() {        return group;    }    public void setGroup(Groups group) {        this.group = group;    } }

③、多对多：定义操作 sql映射文件userMapper.xml

    
        
         
             select g.gid,g.gname from users_groups ug,groups g            where ug.group_id=g.gid and ug.user_id=#{uid}        
             
              
              
                  
               
               
          
          
    

⑤、向 mybatis-configuration.xml 配置文件中注册 userMapper.xml文件

⑥、编写测试类

//多对多：根据根据用户 id 查询所有的用户组信息

@Test    public void testGetGroups(){        String statement = "many.to.many.userMapper.getUsers";        List
    
      listGroup = session.selectList(statement,1);        for(Groups g : listGroup){            System.out.println(g.toString());        }    }
    

https://www.cnblogs.com/ysocean/p/7237499.html