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  • MyBatis的Mapper接口以及Example的实例函数及详解

    一、mapper接口中的方法解析

    mapper接口中的函数及方法:

    二、example实例解析

    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();

    三、应用举例

    1.查询

    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

    ①countByExample()

    UserExample example = new UserExample();
    Criteria criteria = example.createCriteria();
    criteria.andUsernameEqualTo("wyw");
    int count = XxxMapper.countByExample(example);
    //相当于:select count(*) from user where username='wyw'
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  • 原文地址:https://www.cnblogs.com/chenziyu/p/9754792.html
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