mybatis的多對一

package com.jero.pojo3;

<?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">
<!-- 映射文件 -->
<mapper namespace="com.jero.pojo3">
	<!-- 結果集映射的配置標籤 
	屬性說明 id屬性 ，resultMap標籤的標識。 
	type屬性 ，返回值的全限定類名，或類型別名。 
	autoMapping屬性 ，值範圍true（默認值）|false, 設置是否啓動自動映射功能，
	自動映射功能就是自動查找與字段名小寫同名的屬性名，
	並調用setter方法。而設置爲false後，
	則需要在resultMap內明確註明映射關係纔會調用對應的setter方法。 -->
	<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：指的是屬性的類型 -->
        <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>   
		<!-- 根據名稱模糊查詢 只查出名稱對應的數據 -->
		<select id="listProductByName" resultMap="productBean">
          select * from product_  where name like concat('%',#{name},'%')     
        </select>   
</mapper>

<?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">
<!-- 配置的意思 -->
<configuration>
<!-- 寫實體類的別名,,寫了之後可以在寫Sql配置文件
例如<select>標籤中的屬性就可以不用寫實體的具體路徑直接用別名就可以了 -->
    <typeAliases>
      <package name="com.jero.pojo3"/>
    </typeAliases>
    <!-- 環境配置的標籤，配置連接數據庫所需的屬性值 -->
    <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/how2java?characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>
    <!-- 配置映射的文件  -->
    <mappers>
        <mapper resource="com/jero/pojo3/Category.xml"/>
        <mapper resource="com/jero/pojo3/Product.xml"/>
    </mappers>
</configuration>

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;}public void setPrice(float price) {this.price = price;}@Overridepublic String toString() {return "Product [id=" + id + ", name=" + name + ", price=" + price+ "]";}}

package com.jero.pojo3;

import java.util.List;

public class Category {
	private int id;
    private String name;
    
	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;
	}
	
	@Override
	public String toString() {
		return "Category [id=" + id + ", name=" + name  + "]";
	}
    
}

package com.jero.pojo3;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Test {
	public static void main(String[] args){
		//資源文件
		String resource = "mybatis-config3.xml";
		
		try {
			//輸入流,傳入配置好的文件
			InputStream inputStream = Resources.getResourceAsStream(resource);
			//創建sql工廠，讓配置好的文件成爲一個sql工廠
			SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
			//開啓此工廠
			SqlSession sqlSession = sessionFactory.openSession();
			System.out.println("精確查詢：");
			//獲取Product的數據，並存進集合
			List<Product> products = sqlSession.selectList("listProduct");
			//遍歷並打印
			for (Product product : products) {
				System.out.println(product+"product的分類是："+product.getCategory());
			}
			System.out.println("模糊查詢：");
			//將要查詢的字段和字段值存進一個集合映射
			Map<String,Object> params = new HashMap();
			params.put("name","b");
			//將通過模糊查詢得到的數據存進集合
			List<Product> products2 = sqlSession.selectList("listProductByName",params);
			for (Product p : products2) {
				System.out.println(p);
			}
			sqlSession.commit();
			sqlSession.close();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
}

<?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.jero.pojo3">
        <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類型 -->
            <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>