MP用法：

最新推荐文章于 2024-03-09 22:52:00 发布

原创最新推荐文章于 2024-03-09 22:52:00 发布 · 192 阅读

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#spring

本文档展示了如何使用Spring Boot结合MyBatis进行数据库操作，包括基本查询、动态SQL、复杂查询条件和特定字段选择。通过实例演示了用户数据的CRUD操作以及查询优化技巧。

public class TestMP3 {
    @Autowired
    private UserMapper userMapper;

    @Test
    public void select1(){
        //查询id为23的用户
        User user = userMapper.selectById(23);
        System.out.println(user);
    }
    @Test
    public void select2(){
        //查询姓名为潘凤，性别为男的用户
        User user = new User();
        user.setName("潘凤").setSex("男");
        QueryWrapper queryWrapper = new QueryWrapper(user);
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);

    }
    @Test
    public void select3(){
        //查找年龄大于18或者性别为男的用户数据
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.gt("age",18)
                .or()
                .eq("sex","男");
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    @Test
    public void select4(){
        //使用模糊查询查找以精字结尾的用户，并且使用降序排序
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.likeLeft("name","精")
                .orderByDesc("age");
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    @Test
    public void select5(){
//查询id为1,3,6,7的用户
        Integer[] ids = {1,3,6,7};//使用数组
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.in("id",ids);
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    @Test
    //查询名字为空的数据
    public void select6() {
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.isNull("name");
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    //动态sql查询
    //要求：根据name属性和sex属性查询，如果其数据为null，则不参与where条件的拼接
    /**
    API说明:
     *      queryWrapper.gt(判断条件,字段名称,字段值)
     *      判断条件: true  则动态的拼接where条件
     *               false 不会拼接where条件
     *  判断语句:
     *       Boolean sexBoo = (sex !=null) && sex.length()>0;
     */
    @Test
    public void select7(){
        Integer age = 18;
        String sex = null;
        //Boolean sexBoo = (sex !=null) && sex.length()>0;//条件判断
        boolean flag = StringUtils.hasLength(sex);
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.gt(age > 0,"age",age)
                .eq(flag,"sex",sex);
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    @Test
    public void select8(){
        //查询name和age的用户
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("name","age");
        //没有查询的数据以null返回
        List<User> userList = userMapper.selectList(queryWrapper);
        System.out.println(userList);
    }
    @Test
    public void select9(){
        //查询name和age的用户
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.select("name,age");
        //只返回name和age
        List<Map<String,Object>> list = userMapper.selectMaps(queryWrapper);
        System.out.println(list);
    }
    //要求返回第一列数据
    @Test
    public void select10(){
        List<Object> list = userMapper.selectObjs(null);
        System.out.println(list);
    }
}