Mybatis-Plus-Join表连接插件集成过程

<dependency>
    <groupId>com.github.yulichang</groupId>
    <artifactId>mybatis-plus-join-boot-starter</artifactId>
    <version>1.4.5</version>
</dependency>

import icu.mhb.mybatisplus.plugln.base.mapper.JoinBaseMapper;

public interface UserMapper extends JoinBaseMapper<User> {
   
}

import icu.mhb.mybatisplus.plugln.base.service.JoinIService;

public interface UserService extends JoinIService<User> {
   
}

import icu.mhb.mybatisplus.plugln.base.service.impl.JoinServiceImpl;
import org.springframework.stereotype.Service;

@Service
public class UserServiceImpl extends JoinServiceImpl<UserMapper, User> implements UserService {
   
}

// 方式一：通过 Service 直接获取
JoinLambdaWrapper<User> wrapper = userService.joinLambdaWrapper();

// 方式二：手动创建
JoinLambdaWrapper<User> wrapper = new JoinLambdaWrapper<>(User.class);

// 左连接
wrapper.leftJoin(Department.class, Department::getId, User::getDeptId);

// 右连接
wrapper.rightJoin(Department.class, Department::getId, User::getDeptId);

// 内连接
wrapper.innerJoin(Department.class, Department::getId, User::getDeptId);

wrapper.eq(Department::getName, "技术部")
       .like(User::getName, "张")
       .gt(User::getAge, 25);

// 结束当前连接（重要！）
wrapper.end();

// 执行查询
List<UserVO> result = userService.joinList(wrapper, UserVO.class);

public List<UserVO> findUsersWithMultiJoin() {
    JoinLambdaWrapper<User> wrapper = userService.joinLambdaWrapper();
    
    // 第一重连接：部门表
    wrapper.leftJoin(Department.class, Department::getId, User::getDeptId)
           .selectAs(Department::getName, UserVO::getDeptName)
           .end();
    
    // 第二重连接：职位表
    wrapper.leftJoin(Position.class, Position::getUserId, User::getId)
           .eq(Position::getLevel, "P7")
           .selectAs(Position::getName, UserVO::getPositionName)
           .end();
    
    return userService.joinList(wrapper, UserVO.class);
}