Mybaits 一對多 多對一 多對多
阿新 • • 發佈:2020-08-11
Product實體類
public class Product { private int id; private String name; private float price;
private Category category; public Category getCategory() { return category; } public void setCategory(Category category) { this.category = category; }
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; } publicvoid setPrice(float price) { this.price = price; } @Override public String toString() { return "Product [id=" + id + ", name=" + name + ", price=" + price + "]"; } }
Category實體類,提供products的集合
import java.util.List; public class Category { private int id;private String name; List<Product> products; 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 + "]"; } }
category.xml 一對多
<?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.how2java.pojo"> <resultMap type="Category" id="categoryBean"> <id column="cid" property="id" /> <result column="cname" property="name" /> <!-- 一對多的關係 --> <!-- property: 指的是集合屬性的值, ofType:指的是集合中元素的型別 --> <collection property="products" ofType="Product"> <id column="pid" property="id" /> <result column="pname" property="name" /> <result column="price" property="price" /> </collection> </resultMap> <!-- 關聯查詢分類和產品表 --> <select id="listCategory" resultMap="categoryBean"> 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>
product.xml多對一
<?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.how2java.pojo"> <resultMap type="Product" id="productBean"> <id column="pid" property="id" /> <result column="pname" property="name" /> <result column="price" property="price" /> <!-- 多對一的關係 --> <!-- property: 指的是屬性名稱, javaType:指的是屬性的型別 --> <association property="category" javaType="Category"> <id column="cid" property="id"/> <result column="cname" property="name"/> </association> </resultMap> <!-- 根據id查詢Product, 關聯將Orders查詢出來 --> <select id="listProduct" resultMap="productBean"> 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>
Test.java
import java.io.IOException; import java.io.InputStream; import java.util.List; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.how2java.pojo.Category; import com.how2java.pojo.Product; public class TestMybatis { public static void main(String[] args) throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession();
//一對多 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); } } //多對一
List<Product> ps = session.selectList("listProduct"); for (Product p : ps) { System.out.println(p+" 對應的分類是 \t "+ p.getCategory()); }
sescsion.commit();
session.close();
}
}