Spring Boot开发之Mybatis多对多查询
- 一、一对多查询
-
- 1、打开MySQL Workbench，在上篇数据库下新建orders表，并插入一些数据；其中userid对应class表的id
- 2、打开IDEA，打开上次项目，在pojo文件夹下新建Order实体类
- 3、修改Person实体类
- 4、在dao文件夹下新建OrderMapper类
- 5、在resources文件夹的mappers文件夹下新建OrderMapper.xml
- 6、修改PersonMapper类
- 7、修改PersonMapper.xml
- 8、修改service层的PersonServiceImpl实现类
- 9、修改personlist.html
- 10、加上非空判断(这里可写可不写)
- 11、点击运行，1对多查询成功！
- 二、多对多查询
今天接着上次的项目来讲解Mybatis一对多、多对多查询
一、一对多查询
1、打开MySQL Workbench，在上篇数据库下新建orders表，并插入一些数据；其中userid对应class表的id
2、打开IDEA，打开上次项目，在pojo文件夹下新建Order实体类
package com.example.springboot2.pojo;
import lombok.Data;
import java.util.List;
@Data
public class Order {
private int id;
private int totalprice;
private String orderinfo;
private int userid;
}
3、修改Person实体类
private List<Order> orderList;
4、在dao文件夹下新建OrderMapper类
package com.example.springboot.dao;
import com.example.springboot.pojo.Order;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;
@Mapper
public interface OrderMapper {
public List<Order> findOrderByUserId(Integer userid);
}
5、在resources文件夹的mappers文件夹下新建OrderMapper.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.springboot2.dao.OrderMapper">
<select id="findOrderByUserId"
resultType="com.example.springboot2.pojo.Order"
parameterType="Integer">
select * from orders where userid=#{userid}
</select>
</mapper>
6、修改PersonMapper类
public List<Person> findAllPersonOrders();
7、修改PersonMapper.xml
<select id="findAllPersonOrders" resultMap="personOrder">
select * from class
</select>
<resultMap id="personOrder" type="com.example.springboot2.pojo.Person">
<id column="id" property="id"></id>
<result column="age" property="age"></result>
<result column="name" property="name"></result>
<!-- select查询方法 column将class表查询出来的idcardid字段传到findIdcardById方法中-->
<association property="idcardid" javaType="com.example.springboot2.pojo.Idcard" column="idcardid"
select="com.example.springboot2.dao.IdcardMapper.findIdcardById">
</association>
<!-- private List<Order> orderlist;-->
<!-- collection映射到集合对象 column class表查询出来的将返回的id字段传到findOrderByUserId方法中-->
<collection property="orderList"
ofType="com.example.springboot2.pojo.Order"
column="id"
select="com.example.springboot2.dao.OrderMapper.findOrderByUserId">
</collection>
</resultMap>
8、修改service层的PersonServiceImpl实现类
@Override
public List<Person> findAllPerson(){
return personMapper.findAllPersonOrders();
// return personMapper.findAllPersonIdcard2();
}
9、修改personlist.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h1>用户列表</h1>
<a th:href="@{/addperson}">增加页面</a>
<table border="1">
<tr>
<td>学生id</td>
<td>学生年龄</td>
<td>学生姓名</td>
<td>学生学号</td>
<td>学生班级</td>
<td>订单信息</td>
<td>删除</td>
<td>更新</td>
</tr>
<tr th:each="person:${personlist}">
<td th:text="${person.id}">学生id</td>
<td th:text="${person.age}">学生年龄</td>
<td th:text="${person.name}">学生姓名</td>
<td th:text="${person.idcardid.stuid}">学生学号</td>
<td th:text="${person.idcardid.classname}">学生班级</td>
<td>
<ul th:each="order:${person.orderList}">
<li th:text="${order.totalprice}"></li>
<li th:text="${order.orderinfo}"></li>
</ul>
</td>
<th>
<a th:href="@{deletepersonbyid(id=${person.id},idcardid=${person.idcardid.id})}">删除学生</a>
<!-- <a th:href="@{'deletepersonbyid?id='+${person.id}+'&idcardid='+${person.idcardid.id}}">删除学生</a>-->
</th>
<th>
<a th:href="@{/updateperson(id=${person.id},age=${person.age},name=${person.name})}">更新学生</a>
</th>
</tr>
</table>
</body>
</html>
10、加上非空判断(这里可写可不写)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h1>用户列表</h1>
<a th:href="@{/addperson}">增加页面</a>
<table border="1">
<tr>
<td>学生id</td>
<td>学生年龄</td>
<td>学生姓名</td>
<td>学生学号</td>
<td>学生班级</td>
<td>订单信息</td>
<td>删除</td>
<td>更新</td>
</tr>
<tr th:each="person:${personlist}">
<td th:text="${person.id}">学生id</td>
<td th:text="${person.age}">学生年龄</td>
<td th:text="${person.name}">学生姓名</td>
<td th:if="${person.idcardid.stuid} ne null" th:text="${person.idcardid.stuid}">学生学号</td>
<td th:if="${person.idcardid.classname} ne null" th:text="${person.idcardid.classname}">学生班级</td>
<td>
<ul th:if="${person.orderList} ne null" th:each="order:${person.orderList}">
<li th:text="${order.totalprice}"></li>
<li th:text="${order.orderinfo}"></li>
</ul>
</td>
<th>
<a th:href="@{deletepersonbyid(id=${person.id},idcardid=${person.idcardid.id})}">删除学生</a>
<!-- <a th:href="@{'deletepersonbyid?id='+${person.id}+'&idcardid='+${person.idcardid.id}}">删除学生</a>-->
</th>
<th>
<a th:href="@{/updateperson(id=${person.id},age=${person.age},name=${person.name})}">更新学生</a>
</th>
</tr>
</table>
</body>
</html>
11、点击运行，1对多查询成功！
二、多对多查询
1、在数据库中新建product表，并插入一些数据
2、在数据库中新建orders_product表，其中orderid为orders表中id，productid为product表中id
3、在项目pojo文件夹下新建Product实体类
package com.example.springboot2.pojo;
import lombok.Data;
@Data
public class Product {
private int id;
private String name;
private int price;
}
4、修改Order实体类
private List<Product> productList;
5、在dao文件夹下新建ProductMapper类
package com.example.springboot2.dao;
import com.example.springboot2.pojo.Product;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;
@Mapper
public interface ProductMapper {
public List<Product> findProductById(Integer orderid);
}
6、在resources文件夹的mappers文件夹下新建ProductMapper.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.springboot2.dao.ProductMapper">
<!-- 第二步：将订单主键传到中间order_product表中查询商品主键-->
<!-- 第三步：将商品主键传到商品表中查询商品信息-->
<select id="findProductById" resultType="com.example.springboot2.pojo.Product" parameterType="Integer">
select *
from product
where id in (select productid
from orders_product
where orderid = #{orderid})
</select>
</mapper>
7、修改OrderMapper.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.springboot2.dao.OrderMapper">
<select id="findOrderByUserId"
resultMap="orderProduct"
parameterType="Integer">
select * from orders where userid=#{userid}
</select>
<resultMap id="orderProduct"
type="com.example.springboot2.pojo.Order">
<id column="id" property="id"></id>
<result column="totalprice" property="totalprice"></result>
<result column="orderinfo" property="orderinfo"></result>
<collection property="productList"
ofType="com.example.springboot2.pojo.Product"
column="id"
select="com.example.springboot2.dao.ProductMapper.findProductById">
</collection>
</resultMap>
</mapper>
8、修改personlist.html
<div th:each="product:${order.productList}">
<div th:text="${product.name}"></div>
</div>
9、点击运行，多对多查询成功！
