一个分类对应多个产品
参照http://how2j.cn/k/mybatis/mybatis-one-to-many/1089.html
表结构:
- 产品表
create table product_(
id int NOT NULL AUTO_INCREMENT,
name varchar(30) DEFAULT NULL,
price float DEFAULT 0,
cid int ,
PRIMARY KEY (id)
)AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
- 分类表
CREATE TABLE category_ (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(32) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
实体类:
- Product实体类
public class Product {
private int id;
private String name;
private float price;
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 float getPrice() {
return price;
}
public void setPrice(float price) {
this.price = price;
}
@Override
public String toString() {
return "Product [id=" + id + ", name=" + name + ", price=" + price + "]";
}
}
- Category实体类
import java.util.List;
public class Category {
private int id;
private String name;
List<Product> products; //添加product属性
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 List<Product> getProducts() {
return products;
}
public void setProducts(List<Product> products) {
this.products = products;
}
@Override
public String toString() {
return "Category [id=" + id + ", name=" + name + "]";
}
}
映射文件:
- Mybatis映射文件 mybaits.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases>
<package name="com.java.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/java?characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/java/pojo/Category.xml"/>
</mappers>
</configuration>
- category.xml 映射文件
<!--
通过resultMap把数据取出来放在对应的 对象属性里
注: Category的id 字段 和Product的id字段同名,Mybatis不知道谁是谁的,所以需要通过取别名cid,pid来区分。name字段同理。
-->
<?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.java.pojo">
<resultMap type="Category" id="categoryBean">
<id column="cid" property="id" />
<result column="cname" property="name" />
<!-- 一对多的关系 -->
<!-- property: 指的是集合属性的值, ofType:指的是集合中元素的类型 -->
<collection property="products" ofType="Product">
<id column="pid" property="id" />
<result column="pname" property="name" />
<result column="price" property="price" />
</collection>
</resultMap>
<!-- 关联查询分类和产品表 -->
<select id="listCategory" resultMap="categoryBean"> <!-- resultMap的值和上面resultMap的id相同-->
select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname',
p.name 'pname' from category_ c left join product_ p on c.id = p.cid
</select>
</mapper>
运行:
public static void main(String[] args) throws IOException {
String resource = "mybatis.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
List<Category> cs = session.selectList("listCategory");
for (Category c : cs) {
System.out.println(c);
List<Product> ps = c.getProducts();
for (Product p : ps) {
System.out.println("\t"+p);
}
}
session.commit();
session.close();
}