Mybatis程序入门案例

头像
RYGAR
    阅读 8 分钟

    思路：搭建环境--->导入Mybatis--->编写代码--->测试

    1.1、搭建环境

    搭建数据库

    create databases if not exists `mybatis`;

use `mybatis`;

create table if not exists `user`(
    `id` int(20) not null,
    `name` varchar(30) default null,
    `pwd` varchar(30) default null,
    primary key(`id`)
)engine=innodb default charset=utf8;

    插入数据

    insert into `user`(`id`,`name`,`pwd`) values
(1,'孙悟空','123456'),
(2,'猪八戒','111222'),
(3,'唐僧','789456');

    新建项目
    1.新建一个普通的maven项目
    2.删除src目录
    3.导入maven依赖

    <dependencies>
    <!--mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.46</version>
    </dependency>
    
    <!--mybatis-->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    
    <!--junit-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>
<!--在build中配置resources，来防止我们资源导出失败的问题-->
<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

    1.2、创建一个模块

    • 编写Mybaris的核心配置文件

      <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<configuration>
<environments default="development">
  <environment id="development">
    <transactionManager type="JDBC"/>
    <dataSource type="POOLED">
      <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
      <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf-8&amp;serverTimezone=Asia/Shanghai"/>
      <property name="username" value="root"/>
      <property name="password" value="root"/>
    </dataSource>
  </environment>
</environments>
<mappers>
  <mapper resource="com/jialidun/dao/UserMapper/xml"/>
</mappers>
</configuration>

    • 编写mybatis工具类

      package com.jialidun.utils;

//sqlSessionFactory--->sqlSession
public class MybatisUtils{

  private static SqlSessionFactory sqlSessionFactory;
  static{
  try{
      //使用mybatis第一步：获取sqlSessionFactory对象
      String resource = "mybatis-config.xml";
      InputStream inputStream = Resources.getResourceAsStream(resource);
      sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
      }catch(IOException e){
          e.printStackTrace();
      }
  }
//既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
//SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
  public static SqlSession getSqlSession(){
      return sqlSessionFactory.openSession();
  }
}

      1.3、编写代码

    • 实体类

      package com.jialidun.pojo;

@Data
public class User{
  private int id;
  private String name;
  private String pwd;
}

    • Dao接口

      package com.jialidun.dao;

public interface UserDao{
     //查询全部用户
  List<User> getUserList();
  //根据id查询用户
  User getUserById(int id);
  //insert 一个用户
  int addUser(User user);
  //修改用户
  int updateUser(User user);
  //删除用户
  int deleteUser(int id);

}

    • 接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件
      UserMapper.xml

      <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.jialidun.dao.UserDao">

 <!--select查询语句-->
<select id="getUserList" resultType="com.jialidun.pojo.User">
  select * from mybatis.user
</select>

<select id="getUserById" parameterType="int" resultType="com.jialidun.pojo.User">
  select * from mybatis.user where id = #{id}
</select>

<!--对象中的属性，可以直接取出来-->
<insert id="addUser" parameterType="com.jialidun.pojo.User">
   insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd});
</insert>

<update id="updateUser" parameterType="com.jialidun.pojo.User">
     update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id};
</update>

<delete id="deleteUser" parameterType="int">
   delete from mybatis.user where id=#{id};

</delete>

</mapper>

      1.4、测试

      注意点：
      org.apache.ibatis.binding.BindingException:Type interface com.jialidun.dao.UserDao is not know to the MapperRegistry.

      package com.jialidun.dao;

public class UserDaoTest{
  @Test
  public void test(){
      
      //第一步：获得SqlSession对象
      SqlSession sqlSession = MybatisUtils.getSqlSession();
      
      try{
      UserDao userDao= sqlSession.getMapper(UserDao.class);
      List<User> userList = userDao.getUserList();
      
      //方式二：
      //List<User> userList = sqlSession.selectList("com.jialidun.dao.UserDao.getUserList");
      for(User user:userList){
          System.out.println(user);
      }
      }catch(Exception e){
          e.printStackTrace();
      }finally{
          //关闭SqlSession
          sqlSession.close();
      }
  
      
  }
  
  @Test
  public void getUserById(){
     
     SqlSession sqlSession = MybatisUtils.getSqlSession();
     
     UserMapper mapper = sqlSession.getMapper(UserDao.class);
     
    User user = mapper.getUserById(1);
     System.out,println(user);
     sqlSession.close();
  
  
  }
  
  @Test
  public void addUser(){
   SqlSession sqlSession = MybatisUtils.getSqlSession();
     
     UserMapper mapper = sqlSession.getMapper(UserDao.class);
     
    int num = mapper.addUser(4,"沙和尚","444555");
     if(num>0){
       System.out.println("添加用户成功！");
     
     }
     
     //提交事务
     sqlSession.commit();
     sqlSession.close();
  
  }
  
  @Test
  public void updateUser(){
     SqlSession sqlSession = MybatisUtils.getSqlSession();
     
     UserMapper mapper = sqlSession.getMapper(UserDao.class);
     
    mapper.updateUser(new User(4,"悟净","666666"));
     //提交事务
     sqlSession.commit();
     sqlSession.close();
  
  }
  
  @Test
  public void deleteUser(){
     SqlSession sqlSession = MybatisUtils.getSqlSession();
     
     UserMapper mapper = sqlSession.getMapper(UserDao.class);
     
    mapper.deleteUser(4);
    
    //提交事务
    sqlSession.commit();
    
     sqlSession.close();
  
  
  }
}

      可能遇到的问题：
      1.配置文件没有注册
      2.绑定接口错误
      3.方法名不对
      4.返回类型不对
      5.Maven导出资源问题

      2、Mtbatis的CRUD操作

      2.1、namespace

      namespace中的包名要和Dao/mapper接口的包名一致！

      2.2、select

      选择，查询语句

    • id：就是对应的namespace中的方法名；
    • resultType：sql语句执行的返回值！

    • parameterType：参数类型
      1.编写接口

       /根据id查询用户
User getUserById(int id);

      2.编写对应的mapper中的sql语句

      <select id="getUserById" parameterType="int" resultType="com.jialidun.pojo.User">
select * from mybatis.user where id = #{id}
</select>

      3.测试

       @Test
public void getUserById(){
   
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   
   UserMapper mapper = sqlSession.getMapper(UserDao.class);
   
  User user = mapper.getUserById(1);
   System.out,println(user);
   sqlSession.close();


}

      2.3、Insert

      1.编写接口

      //insert 一个用户
int addUser(User user);

      2.编写对应的mapper值得sql

      <!--对象中的属性，可以直接取出来-->
<insert id="addUser" parameterType="com.jialidun.pojo.User">
 insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd});
</insert>

      3.测试

       @Test
public void addUser(){
 SqlSession sqlSession = MybatisUtils.getSqlSession();
   
   UserMapper mapper = sqlSession.getMapper(UserDao.class);
   
  int num = mapper.addUser(4,"沙和尚","444555");
   if(num>0){
     System.out.println("添加用户成功！");
   
   }
   
   //提交事务
   sqlSession.commit();
   sqlSession.close();

}

      2.4、update

      1.编写接口

       //修改用户
int updateUser(User user);

      2.编写对应的mapper值得sql

      <update id="updateUser" parameterType="com.jialidun.pojo.User">
   update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id};
</update>

      3.测试

      @Test
public void updateUser(){
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   
   UserMapper mapper = sqlSession.getMapper(UserDao.class);
   
  mapper.updateUser(new User(4,"悟净","666666"));
   //提交事务
   sqlSession.commit();
   sqlSession.close();

}

      2.5、delete

      1.编写接口

      //删除用户
int deleteUser(int id);

      2.编写对应的mapper值得sql

      <delete id="deleteUser" parameterType="int">
 delete from mybatis.user where id=#{id};

</delete>

      3.测试

      @Test
public void deleteUser(){
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   
   UserMapper mapper = sqlSession.getMapper(UserDao.class);
   
  mapper.deleteUser(4);
  
  //提交事务
  sqlSession.commit();
  
   sqlSession.close();


}

    注意点：

    • 增删改需要提交事务！

    3、分析错误

    • 标签不要匹配错
    • resource绑定mapper，需要使用路径！
    • 程序配置文件必须符合规范！
    • NullPointException，没有注册到资源！
    • maveb资源没有导出问题！
    mybatis
    RYGAR
    1 声望0 粉丝
    « 上一篇
    Mybatis
    下一篇 »
    Mybatis中的map

    引用和评论

    推荐阅读
    头像
    SpringBoot03：yaml配置注入

    RYGAR阅读 3.2k

    头像
    Mybatis&Mysql的常见异常

    玉喵阅读 181

    头像
    Mybatis的Mapper映射文件中的常用标签

    玉喵阅读 176

    头像
    Mybatis的Mapper映射文件中常用标签

    剣藤犬个阅读 155

    头像
    Mapper 映射文件中常用的标签

    无聊的企鹅阅读 154

    0 条评论
    得票最新