我要评论1：添加依赖
<dependency>
<groupid>com.github.yulichang</groupid>
<artifactid>mybatis-plus-join-boot-starter</artifactid>
<version>1.5.3</version>
</dependency>
<!-- 对于的mybaits-plus版本 -->
<dependency>
<groupid>com.baomidou</groupid>
<artifactid>mybatis-plus-boot-starter</artifactid>
<version>3.5.9</version>
</dependency>2：原来写法的mapper类，继承basemapper（其他全部不用修改）
@mapper
public interface usermapper extends basemapper<user> {
}
2-1：修改为的继承mpjbasemapper
@mapper
public interface usermapper extends mpjbasemapper<user> {
}
3：例子
mpjlambdawrapper<doorcontrollersettingsdoorinfodo> doorcontrollersettingsdoorinfodompjlambdawrapper = new mpjlambdawrapper<doorcontrollersettingsdoorinfodo>()
.selectall()
.leftjoin(doorcontrollersettingsdo.class, doorcontrollersettingsdo::getcontrollernumber, doorcontrollersettingsdo::getcontrollernumber);
doorcontrollersettingsmapper.selectjoinlist(doorcontrollersettingsdo2.class, doorcontrollersettingsdo2mpjlambdawrapper);4：对于selectcollection和selectassociation的使用
4-1：user 实体类
@data
@tablename("user")
public class user {
@tableid
private long id;
private string username;
private string password;
private integer age;
private string email;
}
4-2：address 实体类
@data
@tablename("address")
public class address {
@tableid
private long id;
private long userid; // 外键，关联user.id
private string province;
private string city;
private string district;
private string detail;
}
4-3：userdto 数据传输对象
@data
public class userdto {
private long id;
private string username;
private string password;
private integer age;
private string email;
// 使用list接收一对多关系
private list<address> addresslist;
}
4-4：usermapper代码查询
mpjlambdawrapper<user> wrapper = new mpjlambdawrapper<user>()
.selectall(user.class)
//全部映射 不用考虑字段名重复问题(比如 id), 会对重复列自动添加别名
.selectcollection(address.class, userdto::getaddresslist)
.leftjoin(address.class, address::getuserid, user::getid);
list<userdto> dtolist= usermapper.selectjoinlist(userdto.class, wrapper);
4-5：生成的sql语句，基于mpjlambdawrapper代码，mybatis-plus-join会生成如下sql：
select
user.id as user_id,
user.username as user_username,
user.password as user_password,
user.age as user_age,
user.email as user_email,
address.id as address_id,
address.user_id as address_user_id,
address.province as address_province,
address.city as address_city,
address.district as address_district,
address.detail as address_detail
from
user
left join
address on address.user_id = user.id4-6：执行结果生成sql处理，mybatis-plus-join会自动处理结果集，将数据映射为：
list<userdto> dtolist = [
{
"id": 1,
"username": "张三",
"password": "123456",
"age": 25,
"email": "zhangsan@example.com",
"addresslist": [
{
"id": 1,
"userid": 1,
"province": "北京",
"city": "北京市",
"district": "海淀区",
"detail": "中关村大街1号"
},
{
"id": 2,
"userid": 1,
"province": "上海",
"city": "上海市",
"district": "浦东新区",
"detail": "张江高科技园区"
}
]
},
]注意
//使用如下方法 joinwrappers.lambda(doorcontrollersettingsdoorinfodo.class) //替换 new mpjlambdawrapper<doorcontrollersettingsdoorinfodo>() //使用如下方法 wrappers.lambda(doorcontrollersettingsdoorinfodo.class) //替换 new lambdawrapper<doorcontrollersettingsdoorinfodo>()
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