MyBatis的Mapper接口以及Example的实例函数及详解

mybatis的逆向工程中会生成实例及实例对应的example，example用于添加条件，相当where后面的部分

xxxExample example = new xxxExample();

Criteria criteria = new Example().createCriteria();

| 方法 | 说明 |

| — | — |

| example.setOrderByClause(“字段名 ASC”); | 添加升序排列条件，DESC为降序 |

| example.setDistinct(false) | 去除重复，boolean型，true为选择不重复的记录。 |

| criteria.andXxxIsNull | 添加字段xxx为null的条件 |

| criteria.andXxxIsNotNull | 添加字段xxx不为null的条件 |

| criteria.andXxxEqualTo(value) | 添加xxx字段等于value条件 |

| criteria.andXxxNotEqualTo(value) | 添加xxx字段不等于value条件 |

| criteria.andXxxGreaterThan(value) | 添加xxx字段大于value条件 |

| criteria.andXxxGreaterThanOrEqualTo(value) | 添加xxx字段大于等于value条件 |

| criteria.andXxxLessThan(value) | 添加xxx字段小于value条件 |

| criteria.andXxxLessThanOrEqualTo(value) | 添加xxx字段小于等于value条件 |

| criteria.andXxxIn(List<？>) | 添加xxx字段值在List<？>条件 |

| criteria.andXxxNotIn(List<？>) | 添加xxx字段值不在List<？>条件 |

| criteria.andXxxLike(“%”+value+”%”) | 添加xxx字段值为value的模糊查询条件 |

| criteria.andXxxNotLike(“%”+value+”%”) | 添加xxx字段值不为value的模糊查询条件 |

| criteria.andXxxBetween(value1,value2) | 添加xxx字段值在value1和value2之间条件 |

| criteria.andXxxNotBetween(value1,value2) | 添加xxx字段值不在value1和value2之间条件 |

三、应用举例

① selectByPrimaryKey()

User user = XxxMapper.selectByPrimaryKey(100); //相当于select * from user where id = 100

② selectByExample() 和 selectByExampleWithBLOGs()

UserExample example = new UserExample();

Criteria criteria = example.createCriteria();

criteria.andUsernameEqualTo(“wyw”);

criteria.andUsernameIsNull();

example.setOrderByClause(“username asc,email desc”);

List<?>list = XxxMapper.selectByExample(example);

//相当于：select * from user where username = ‘wyw’ and username is null order by username asc,email desc

注：在iBator逆向工程生成的文件XxxExample.java中包含一个static的内部类Criteria，Criteria中的方法是定义SQL 语句where后的查询条件。

2.插入数据

①insert()

User user = new User();

user.setId(“dsfgsdfgdsfgds”);

user.setUsername(“admin”);

user.setPassword(“admin”)

user.setEmail(“wyw@163.com”);

XxxMapper.insert(user);

//相当于：insert into user(ID,username,password,email) values (‘dsfgsdfgdsfgds’,‘admin’,‘admin’,‘wyw@126.com’);

3.更新数据

①updateByPrimaryKey()

User user =new User();

user.setId(“dsfgsdfgdsfgds”);

user.setUsername(“wyw”);

user.setPassword(“wyw”);

user.setEmail(“wyw@163.com”);

XxxMapper.updateByPrimaryKey(user);

//相当于：update user set username=‘wyw’, password=‘wyw’, email=‘wyw@163.com’ where id=‘dsfgsdfgdsfgds’

②updateByPrimaryKeySelective()

User user = new User();

user.setId(“dsfgsdfgdsfgds”);

user.setPassword(“wyw”);

XxxMapper.updateByPrimaryKey(user);

//相当于：update user set password=‘wyw’ where id=‘dsfgsdfgdsfgds’

③ updateByExample() 和 updateByExampleSelective()

UserExample example = new UserExample();

Criteria criteria = example.createCriteria();

criteria.andUsernameEqualTo(“admin”);

User user = new User();

user.setPassword(“wyw”);

XxxMapper.updateByPrimaryKeySelective(user,example);

//相当于：update user set password=‘wyw’ where username=‘admin’

updateByExample()更新所有的字段，包括字段为null的也更新，建议使用 updateByExampleSelective()更新想更新的字段

4.删除数据

①deleteByPrimaryKey()

XxxMapper.deleteByPrimaryKey(1); //相当于：delete from user where id=1

②deleteByExample()

UserExample example = new UserExample();

Criteria criteria = example.createCriteria();

criteria.andUsernameEqualTo(“admin”);

XxxMapper.deleteByExample(example);

//相当于：delete from user where username=‘admin’

5.查询数据数量