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ORM 

对象关系映射；以面向对象的方法与数据交互。

实体对象与表一 一映射 ，对象属性与表的字段一 一映射；

一行数据代表一个实体对象，即表是实体对象的集合，

@TableName("数据库中的表名")public class 类名{@TaleId(type = Idtype.AUTO)//主键注解，主键自增@TableFiled("字段名")//字段注解实体类的属性与数据库中的字段一致，可以省略}

/@Mapper//管理接口对象，为接口对象创建反射机制一个对象//代理对象//BaseMapper
   
    T表示MP要操作的表 泛型public interface UserMapper extends BaseMapper
    
      {   List
     
       findAll();//接口方法 ，   @Insert("insert into demo_user(id,name,age,sex) values(null,#{name},#{age},#{sex})")   void insertUser (User user);   @Update("update demo_user set name = #{newName} where name = #{oldName}")   void updateByName(String oldName, String newName);   @Delete("delete from demo_user where name = #{name}")   void deleteByName(String name);}
     
    
   

MyBatis CRUD

@Test    public void insertUser(){        User user = new User();        user.setName("星期五").setAge(18).setSex("男");        userMapper.insertUser(user);        System.out.println("新增成功");    }    @Test    public void updateUser(){        String newName = "星期六";        String oldName = "星期五";        userMapper.updateByName(newName, oldName);        System.out.println("修改成功");    }    @Test    public void deleteUser(){       String name = "星期六";        userMapper.deleteByName(name);        System.out.println("删除成功");    }    @Test    public void testInserts(){        User user = new User();        user.setName("张三").setAge(21).setSex("男");        userMapper.insertUser(user);        System.out.println("成功");    }    @Test    public void insertEmp(){        Emp emp = new Emp();        empMapper.insertEmp(emp);    }    @Test    public void updateByName(){        String oldName = "李四";        String newName = "李伟";        empMapper.updateByName(oldName,newName);    }    @Test    public void deleteByName(){        String name = "李伟";        empMapper.deleteByName(name);    }    @Test    public void selectAll(){        List
   
     emps = empMapper.selectAll();        List
    
      emps1 = empMapper.selectList(null);        System.out.println(emps);        System.out.println(emps1);    }
    
   

MP中的转义字符

@Test    public void select03(){        QueryWrapper
   
     queryWrapper = new QueryWrapper<>();        queryWrapper.gt("age" , 18)                .or()//开启or                .eq("sex", "男");        User user = userMapper.selectById(queryWrapper);        System.out.println(user);    }    /**查询name中 包含精 按年龄降序*/    @Test    public void select04(){        QueryWrapper
    
      queryWrapper = new QueryWrapper<>();//       queryWrapper.like("name", "精")//               .orderByDesc("age");        queryWrapper.likeRight("name", "精")//                相当于精%  likeLeft("name","精")；==精%                .orderByDesc("age");        User user = userMapper.selectById(queryWrapper);        System.out.println(user);    }//    查询id 为 1,3,6,7    @Test    public void select05(){        Integer[] ids = {1,3,6,7};        QueryWrapper
     
       queryWrapper = new QueryWrapper<>();        queryWrapper.in("id",ids );        List
      
        users = userMapper.selectList(queryWrapper);        System.out.println(users);    }//    查询name为null的数据    @Test    public void select06(){        QueryWrapper
       
         queryWrapper = new QueryWrapper<>();        queryWrapper.isNull("name");        List
        
          users = userMapper.selectList(queryWrapper); System.out.println(users); }// condition boolean 类型 true 拼接，否则不拼接 @Test public void select07(){ Integer age = 18; String sex = null;// boolean flag = sex != null && sex.length()>0; boolean flag = StringUtils.hasLength(sex);// 等价于上面的 spring框架的API StringUtils.hasLength(sex); QueryWrapper
         
           queryWrapper = new QueryWrapper<>(); queryWrapper.gt(age>0, "age", age).eq("sex", sex); List
          
            users = userMapper.selectList(queryWrapper); System.out.println(users); } @Test public void selectTest(){ Integer age = 18; String sex = null;// boolean flag = sex != null && sex.length()>0; boolean flag = StringUtils.hasLength(sex);// 等价于上面的 spring框架的API StringUtils.hasLength(sex); QueryWrapper
           
             queryWrapper = new QueryWrapper<>(); queryWrapper.gt(age>0, "age", age).eq("sex", sex); List
            
              users = userMapper.selectList(queryWrapper); System.out.println(users); }// 只查询name，age字段信息// select挑选需要查询的信息// 此时会返回所有数据，没查询的为null @Test public void select08(){ QueryWrapper
             
               queryWrapper = new QueryWrapper<>(); queryWrapper.select("name","age"); List
              
                users = userMapper.selectList(queryWrapper); System.out.println(users); }// 只查询name，age, @Test public void select09(){ QueryWrapper
               
                 queryWrapper = new QueryWrapper<>(); queryWrapper.select("name","age"); List
                
               
              
             
            
           
          
         
        
       
      
     
    
   

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