The use of Mybatis-plus dynamic condition query QueryWrapper

The use of Mybatis-plus dynamic condition query QueryWrapper

1: Introduction to queryWrapper

queryWrapper is an object encapsulation operation class that implements query in mybatis plus. It can encapsulate sql objects, including where conditions, order by sorting, which fields to select, etc. Its hierarchical relationship is as follows:

Wrapper：条件构造抽象类，最顶端父类；
AbstractWrapper：用于查询条件封装，生成sql的where条件；
AbstractLambdaWrapper：Lambda语法使用Wrapper统一处理解析lambda获取column。
LambdaQueryWrapper：用于lambda语法使用的查询Wrapper；
LambdaUpdateWrapper:Lambda更新封装Wrapper;
QueryWrapper:Entity对象封装操作类，不是用lambda；
UpdateWrapper:Update条件封装，用于Entity对象更新操作。

2: queryWrapper example

2.1-Case 1: Fuzzy view of undeleted user list information based on name

Filter criteria:

name 用户名称 ，模糊查看
del_flag = 0
按照create_time创建时间降序
sql实现:

select * from t_user
where del_flag = 0
<if test ="name!=null and ''!=name">
    and name like concat('%',#{name},'%')
</if>
order by create_time desc

queryWrapper implementation:

/**
 * 案例一：根据name模糊查看未删除的用户列表信息
 * @param name
 * @return
 */
@RequestMapping("/list")
public Map<String,Object> getList(@RequestParam String name){
    Map<String,Object> result = new HashMap<>();

	//构建一个查询的wrapper
    QueryWrapper<User> wrapper = new QueryWrapper<User>();
    //name不为空时，组装模糊查询条件
    wrapper.like(StringUtils.isNotBlank(name),"name",name);
    //未删除
    wrapper.eq("del_flag",0);
    //创建时间降序
    wrapper.orderByDesc("create_time");

    List<User> list = userMapper.selectList(wrapper);
    result.put("data",list);
    return result;
}

2.2-Case 2: Check the list of users whose surname is Li and whose email address is not empty

sql implementation:

select * from t_user
where del_flag = 0
and name like concat('李','%')
and email is not null
order by create_time desc

queryWrapper implementation:

/**
 * 案例二：查看姓张的并且邮箱不为空的用户列表
 * @return
 */
@RequestMapping("/list2")
public Map<String,Object> getList2(){
    Map<String,Object> result = new HashMap<>();

    //构建一个查询的wrapper
    QueryWrapper<User> wrapper = new QueryWrapper<User>();
    //姓张的
    wrapper.likeRight("name","张");
    //邮箱不为空
    wrapper.isNotNull("email");
    //未删除
    wrapper.eq("del_flag",0);
    //创建时间降序
    wrapper.orderByDesc("create_time");

    List<User> list = userMapper.selectList(wrapper);
    result.put("data",list);
    return result;
}

2.3-Case 3: Age range query (between 20-30)

sql implementation:

select * from t_user
where del_flag=0
and age between 20 and 30
order by create_time desc

queryWrapper implementation:

/**
 * 案例三：年龄范围查询（20-30之间的）
 * @return
 */
@RequestMapping("/list3")
public Map<String,Object> getList3(){
    Map<String,Object> result = new HashMap<>();

    //构建一个查询的wrapper
    QueryWrapper<User> wrapper = new QueryWrapper<User>();
    //年龄20-30之间的
    wrapper.between("age",20,30);
    //未删除
    wrapper.eq("del_flag",0);
    //创建时间降序
    wrapper.orderByDesc("create_time");

    List<User> list = userMapper.selectList(wrapper);
    result.put("data",list);
    return result;
}