一、mapper介面中的方法解析

mapper介面中的函式及方法

二、example例項解析

mybatis的逆向工程中會生成例項及例項對應的example，example用於新增條件，相當where後面的部分

三、應用舉例

1.查詢

① selectByPrimaryKey()

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

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② selectByExample() 和 selectByExampleWithBLOGs()

1. UserExample example = new UserExample();
2. Criteria criteria = example.createCriteria();
3. criteria.andUsernameEqualTo("wyw");
4. criteria.andUsernameIsNull();
5. example.setOrderByClause("username asc,email desc");
6. List<?>list = XxxMapper.selectByExample(example);
7. //相當於：select * from user where username = 'wyw' and username is null order by username asc,email desc

注：在iBator逆向工程生成的檔案XxxExample.java中包含一個static的內部類Criteria，Criteria中的方法是定義SQL 語句where後的查詢條件。

2.插入資料

①insert()

1. User user = new User();
2. user.setId("dsfgsdfgdsfgds");
3. user.setUsername("admin");
4. user.setPassword("admin")
5. user.setEmail("[email protected]");
6. XxxMapper.insert(user);
7. //相當於：insert into user(ID,username,password,email) values ('dsfgsdfgdsfgds','admin','admin','[email protected]');

3.更新資料

①updateByPrimaryKey()

1. User user =new User();
2. user.setId("dsfgsdfgdsfgds");
3. user.setUsername("wyw");
4. user.setPassword("wyw");
5. user.setEmail("[email protected]");
6. XxxMapper.updateByPrimaryKey(user);
7. //相當於：update user set username='wyw', password='wyw', email='[email protected]' where id='dsfgsdfgdsfgds'

②updateByPrimaryKeySelective()

1. User user = new User();
2. user.setId("dsfgsdfgdsfgds");
3. user.setPassword("wyw");
4. XxxMapper.updateByPrimaryKey(user);
5. //相當於：update user set password='wyw' where id='dsfgsdfgdsfgds'

③ updateByExample() 和 updateByExampleSelective()

1. UserExample example = new UserExample();
2. Criteria criteria = example.createCriteria();
3. criteria.andUsernameEqualTo("admin");
4. User user = new User();
5. user.setPassword("wyw");
6. XxxMapper.updateByPrimaryKeySelective(user,example);
7. //相當於：update user set password='wyw' where username='admin'

updateByExample()更新所有的欄位，包括欄位為null的也更新，建議使用 updateByExampleSelective()更新想更新的欄位

4.刪除資料

①deleteByPrimaryKey()

XxxMapper.deleteByPrimaryKey(1);  //相當於：delete from user where id=1

②deleteByExample()

1. UserExample example = new UserExample();
2. Criteria criteria = example.createCriteria();
3. criteria.andUsernameEqualTo("admin");
4. XxxMapper.deleteByExample(example);
5. //相當於：delete from user where username='admin'

5.查詢資料數量

①countByExample()

1. UserExample example = new UserExample();
2. Criteria criteria = example.createCriteria();
3. criteria.andUsernameEqualTo("wyw");
4. int count = XxxMapper.countByExample(example);