【Mybatis】级联查询之多对多级联查询
目录
- 引言
- 创建工程和数据库表
- 创建实体类和数据库操作接口
-
- Order 类
- Product 类
- OrderMapper 类
- ProductMapper 类
- 创建配置文件
-
- mybatis-config.xml
- OrderMapper.xml
- ProductMapper.xml
- 添加测试代码
引言
在Mybatis中，多对多的级联查询通常会转成两个一对多级联查询来实现
应用场景举例：用户与商品之间的关系为多对多， 一个订单可以有多种商品，使用一个中间表（订单记录表）就可以将多对多级联转换成两个一对多的关系
创建工程和数据库表
创建Spring整合Mybatis工程 【Spring】Spring整合Mybatis案例
创建orders表、product表和 order_product表
DROP TABLE IF EXISTS `orders`;
CREATE TABLE `orders` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`orderinfo` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS `product`;
CREATE TABLE `product` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
`price` double(10,2) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS `order_product`;
CREATE TABLE `order_product` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`order_id` int(11) DEFAULT NULL,
`product_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `order_id` (`order_id`),
KEY `product_id` (`product_id`),
CONSTRAINT `order_id` FOREIGN KEY (`order_id`) REFERENCES `orders` (`id`),
CONSTRAINT `product_id` FOREIGN KEY (`product_id`) REFERENCES `product` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
项目结构如下：
创建实体类和数据库操作接口
Order 类
public class Order {
private int id;
private String orderinfo;
// 多对多中的另一个一对多
private List<Product> products;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getOrderinfo() {
return orderinfo;
}
public void setOrderinfo(String orderinfo) {
this.orderinfo = orderinfo;
}
public List<Product> getProducts() {
return products;
}
public void setProducts(List<Product> products) {
this.products = products;
}
@Override
public String toString() {
return "Order{" +
"id=" + id +
", orderinfo='" + orderinfo + '\'' +
", products=" + products +
'}';
}
}
Product 类
public class Product {
private int id;
private String name;
private double price;
// 多对多中的一个一对多
private List<Order> orders;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public List<Order> getOrders() {
return orders;
}
public void setOrders(List<Order> orders) {
this.orders = orders;
}
@Override
public String toString() {
return "Product{" +
"id=" + id +
", name='" + name + '\'' +
", price=" + price +
", orders=" + orders +
'}';
}
}
OrderMapper 类
@Repository("orderMapper")
@Mapper
public interface OrderMapper {
List<Order> findAllOrdersAndProduct();
}
ProductMapper 类
@Repository("productMapper")
@Mapper
public interface ProductMapper {
List<Product> findAllProductAndOrders();
}
创建配置文件
mybatis-config.xml
<configuration>
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>
settings>
<mappers>
<mapper resource="ProductMapper.xml"/>
<mapper resource="OrderMapper.xml"/>
mappers>
configuration>
OrderMapper.xml
<mapper namespace="com.lucas.mybatis.mapper.OrderMapper">
<resultMap id="orderAndProducts" type="com.lucas.mybatis.model.Order">
<id property="id" column="id">id>
<result property="orderinfo" column="orderinfo">result>
<collection property="products" ofType="com.lucas.mybatis.model.Product" >
<id property="id" column="id">id>
<result property="name" column="name">result>
<result property="price" column="price">result>
collection>
resultMap>
<select id="findAllOrdersAndProduct" resultMap="orderAndProducts">
SELECT orders.*,product.id,product.`name`,product.price FROM orders,product,order_product WHERE orders.id = order_product.order_id AND order_product.product_id = product.id;
select>
mapper>
ProductMapper.xml
<mapper namespace="com.lucas.mybatis.mapper.ProductMapper">
<resultMap id="productAndOrders" type="com.lucas.mybatis.model.Product">
<id property="id" column="id">id>
<result property="name" column="name">result>
<result property="price" column="price">result>
<collection property="orders" ofType="com.lucas.mybatis.model.Order" >
<id property="id" column="id">id>
<result property="orderinfo" column="orderinfo">result>
collection>
resultMap>
<select id="findAllProductAndOrders" resultMap="productAndOrders">
SELECT product.*,orders.id,orders.orderinfo FROM orders,product,order_product WHERE orders.id = order_product.order_id AND order_product.product_id = product.id;
select>
mapper>
添加测试代码
public class App {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
OrderMapper orderMapper = (OrderMapper) applicationContext.getBean("orderMapper");
System.out.println("----订单列表-----");
List<Order> orders = orderMapper.findAllOrdersAndProduct();
for (Order order : orders) {
System.out.println(order);
}
System.out.println("----商品列表列表-----");
ProductMapper productMapper = (ProductMapper) applicationContext.getBean("productMapper");
List<Product> products = productMapper.findAllProductAndOrders();
for (Product product : products) {
System.out.println(product);
}
}
}
运行结果如下：
