MyBatis入门和基本的CRUD

1. 添加MyBatis坐标
2. 创建User数据表
3. 创建User实体类
4. 编写映射文件UserMapper.xml文件
5. 编写核心文件SqlMapConfig文件
6. 编写测试类

1.添加MyBatis坐标

        
            org.mybatis
            mybatis
            3.4.5
        

        
            mysql
            mysql-connector-java
            8.0.27
        

        
            org.apache.isis.viewer
            junit
            0.1.2-incubating
        

        
            log4j
            log4j
            1.2.17
        

2.第二步：创建数据表（包含字段id、username、password）

CREATE TABLE IF NOT EXISTS  USER(
	id INT PRIMARY KEY AUTO_INCREMENT,
	username VARCHAR(52) NOT NULL,
	PASSWORD VARCHAR(52) NOT NULL
);

INSERT INTO USER VALUES(NULL,'海康','123'),
(NULL,'湛江','123'),(NULL,'南宁','123');

SELECt * FROM USER;

3.第三步：创建User实体

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString 
public class User{
	private int id;
	private String username;
	private String password;
}

4.第四步：编写映射文件UserMapper.xml文件

    表示查询全部
    
        select * from user
    

5.第五步：编写sqlMapConfig.xml文件

    
        
            transactionManager：事务布局器
            
            
                
                
                
                
            
        
    


    
        
    

mapper resource=“com/haikang/mapper/UserMapper.xml”

注意是“/”

6.测试类编写

1. 加载配置文件：Resources.getResourceStream(“加载文件名”);
2. 获得构sqlSession工厂对象：SqlSessionFactoryBuilder().build(“加载文件返回值”);
3. 获得sqlSession对象
4. 执行Sql语句
5. 打印数据
6. 关流

  //加载配置文件
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    //获得sqlSession工厂对象
    SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
    //获得SqlSession对象
    SqlSession sqlSession = build.openSession();
    //执行Sql语句
    List user = sqlSession.selectList("userMapper.findAll");

    for (User users:
         user) {
        System.out.println(users);
    }

    sqlSession.close();
}

MyBatis的映射文件概述：

步骤：

1.编写UserMapper映射文件

    
        insert into user (id,username,password) values (#{id},#{username},#{password})
    

2.编写测试类：注意是由于MyBatis默认是不提交事务的，必须手动提交事务

 @Test
    public void test2() throws IOException {
        //加载配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        //获得SqlSession工厂对象
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //获得SqlSession对象
        SqlSession sqlSession = build.openSession();
        //执行Sql语句
        int insert = sqlSession.insert("userMapper.add", new User(5, "海康", "123456"));
        System.out.println(insert);
        //注意是:由于MyBatis默认是不提交事务的，不像JDBC
        sqlSession.commit();
        //关流
        sqlSession.close();
    }

MyBatis的插入数据操作的注意问题：

1. 插入语句使用insert标签
2. 在映射 文件中使用parameterType属性指定要插入的数据类型
3. Sql语句中使用#{实体属性名}方式引用实体中的属性值
4. 插入操作使用API是sqlSession.insert(“命名空间.id”,实体对象);
5. 插入操作涉及的数据库数据变化，所以使用sqlSession对象显示的提交事务，即sqlSession.commit()

MyBatis的修改数据操作步骤：

1.编写UserMapper.xml文件

2.编写测试类

    
        update user set  username=#{username} where id=#{id}
    

@Test
public void test4() throws IOException {
    User user = new User();
    user.setId(2);
    //加载配
    置文件
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    //获得SqlSession工厂对象
    SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
    //获得SqlSession对象
    SqlSession sqlSession = build.openSession();
    //执行sql语句
    int delete = sqlSession.delete("userMapper.delete", user);
    System.out.println(delete);
    //提交事务
    sqlSession.commit();
    //关流
    sqlSession.close();
}

MyBatis的修改数据操作注意点：

• 修改语句使用update标签
• 修改操作使用API是SqlSession.update(“命名空间.id”,实体对象)

步骤：

1. 编写UserMapper.xml文件
2. 编写测试类

    
        delete from user  where id=#{id}
    


    
        delete from user where id=#{id}
    

@Test
public void test4() throws IOException {
    User user = new User();
    user.setId(2);
    //加载配置文件
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    //获得SqlSession工厂对象
    SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
    //获得SqlSession对象
    SqlSession sqlSession = build.openSession();
    //执行sql语句
    int delete = sqlSession.delete("userMapper.delete", user);
    System.out.println(delete);
    //提交事务
    sqlSession.commit();
    //关流
    sqlSession.close();
}

@Test
public void test5() throws IOException {
    //加载配置文件
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    //获得SqlSess工厂对象
    SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
    //获得SqlSess对象
    SqlSession sqlSession = build.openSession();
    //执行Sql语句
    int delete = sqlSession.delete("userMapper.delete", 5);
    System.out.println(delete);
    //提交事务
    sqlSession.commit();
    //关流
    sqlSession.close();
}