mybatisplus左连接查询

在MyBatis Plus中进行左连接查询，你可以使用Wrapper对象来构建查询条件。以下是一个示例代码：

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.example.demo.entity.User;
import com.example.demo.entity.UserDetail;
import com.example.demo.mapper.UserMapper;
import com.example.demo.mapper.UserDetailMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    @Autowired
    private UserDetailMapper userDetailMapper;

    public IPage<User> getUsersWithDetails() {
        // 构建分页对象
        IPage<User> page = new Page<>(1, 10);

        // 构建查询条件
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("status", 1);

        // 执行查询
        IPage<User> result = userMapper.selectPage(page, queryWrapper);

        // 返回查询结果
        return result;
    }

    public User getUserWithDetail(Long userId) {
        // 构建查询条件
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("id", userId);

        // 执行查询
        User user = userMapper.selectOne(queryWrapper);

        if (user != null) {
            // 构建查询条件
            QueryWrapper<UserDetail> detailQueryWrapper = new QueryWrapper<>();
            detailQueryWrapper.eq("user_id", user.getId());

            // 执行左连接查询
            UserDetail userDetail = userDetailMapper.selectOne(detailQueryWrapper);

            // 设置关联对象
            user.setUserDetail(userDetail)