mybatis Plus 实现多表联合查询的方法

//实体类package com.sk.skkill.entity;


import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

import java.io.Serializable;
import java.util.Date;
import java.util.List;


@TableName("orders")
@Data
public class Order implements Serializable
{
  public static final long serialVersionUID =1L;
  private String id;
  private String orderName;
  private Date createTime;
  private Date updateTime;
  private String userID;

  @TableField(exist = false)
  private List<Users> listUsers;


  public Order(){

  }

  public Order(String id, String orderName) {
    this.id = id;
    this.orderName = orderName;
  }
}

//dao层
package com.sk.skkill.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.sk.skkill.entity.Order;
import com.sun.javafx.collections.MappingChange;
import org.apache.ibatis.annotations.Select;

import java.util.List;
import java.util.Map;

public interface OrderMapper extends BaseMapper<Order>
{
List<Order> selectOrder();
int addOrder(Order order);

//多表联合查询 按条件orderID
@Select("select t1.*,t2.user_name,t2.nick_name from orders t1 LEFT JOIN users t2 ON t1.user_id =t2.id WHERE t1.user_id= #{id}")
 List<Map<String,Object>> orderUserList(Page<Map<String,Object>> page,String id);

}

//service层
package com.sk.skkill.service;

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.IService;
import com.sk.skkill.entity.Order;

import java.util.List;
import java.util.Map;

public interface OrderService extends IService<Order>
{
  List<Order> selectOrder();
  int addOrder(Order order);
//  List<Map<String,Object>> orderUserList(Page<Map<String,Object>> page, String id);
  Page<Map<String,Object>> selectListPage(int current,int number,String id);
}

//serviceImpl层
package com.sk.skkill.service.impl;

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.sk.skkill.entity.Order;
import com.sk.skkill.mapper.OrderMapper;
import com.sk.skkill.service.OrderService;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Map;

@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements OrderService
{

  @Override
  public List<Order> selectOrder() {
    return baseMapper.selectList(null);
  }

  @Override
  public int addOrder(Order order) {
    return baseMapper.insert(order);
  }

  @Override
  public Page<Map<String, Object>> selectListPage(int current, int number,String id) {
    //新建分页
    Page<Map<String,Object>> page =new Page<Map<String,Object>>(current,number);
    //返回结果
    return page.setRecords(this.baseMapper.orderUserList(page,id));
  }
}

//controller层 
package com.sk.skkill.controller;

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.sk.skkill.entity.Order;
import com.sk.skkill.service.impl.OrderServiceImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;
import java.util.Map;

@RestController
@RequestMapping("order")
public class OrderController
{
  @Autowired
  private OrderServiceImpl service;

  @RequestMapping("selectOrder")
  public List<Order> selectOrder()
  {
    return service.selectOrder();
  }
  @RequestMapping("addOrder")
 public int addOrder(Order order){
    order=new Order("FGGG","蒙牛MILK");
    return service.addOrder(order);

 

 }
 @RequestMapping("selectListPage")
  public List<Map<String,Object>>  selectListPage(String id)
  {
    Page<Map<String, Object>> page = service.selectListPage(1, 2,id);
    return page.getRecords();
  }
}