mybatis3.2.7學習筆記2_一對一、一對多、多對多、延時載入、快取
阿新 • • 發佈：2019-02-18
參考源：
我對比了一下mybatis和hibernate的一對一 一對多 多對多的概念
mybatis的要比hibernate簡單的多 更加突出了mybatis注重sql的概念
* resuType--將sql的列名和pojo的屬性進行一一的對映 * resultMap--可以避免使用resultType方式的重複記錄 * association--將sql列對映到pojo物件中 collection--將關聯資訊對映到list列表中 * association、collection都具備延時載入功能 mybatis具有二級快取 * SqlSession--一級快取，當SqlSession未關閉時，使用key-value的形式儲存物件，當進行增加、刪除、修改時，都會清空一級快取中的資料 * Mapper名稱空間--二級快取，二級快取的介面為Cache * ，mybatis提供的二級快取預設實現為PerpetualCache，以Mapper的名稱空間為單位進行快取 * ，可跨多個SqlSession，當SqlSession關閉時 * ，將一級快取的物件寫入到二級快取，要進行二級快取的物件必須序列化，因為二級快取不一定在記憶體中，可能在硬碟 * 當進行增加、刪除、修改時，都會清空二級快取中的資料
* useCache="true"
* flushCache="true"Mapper的配置檔案
<?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"> <!-- 使用Mapper代理開發 namespace的值與mapper的介面包 --> <mapper namespace="com.undergrowth.mybatis.mapper.OrderUserMapper"> <!-- 使用resultType進行一對一的對映 --> <select id="findOrdersUserByResultType" resultType="com.undergrowth.mybatis.po.OrdersUser"> select orders.*,user.username,user.birthday from orders,user where orders.user_id=user.id </select> <!-- 使用resultMap進行一對一的對映 --> <resultMap type="com.undergrowth.mybatis.po.OrdersUserPojo" id="findOrdersUserByResultMapId"> <result column="id" property="id" /> <result column="user_id" property="user_id" /> <result column="number" property="number" /> <result column="createtime" property="createtime" /> <result column="note" property="note" /> <association property="user" javaType="com.undergrowth.mybatis.po.User"> <result column="username" property="username" /> <result column="birthday" property="birthday" /> </association> </resultMap> <!-- 使用resultMap進行一對一的對映 --> <select id="findOrdersUserByResultMap" resultMap="findOrdersUserByResultMapId"> select orders.*,user.username,user.birthday from orders,user where orders.user_id=user.id </select> <!-- 使用collection進行集合元素的對映 對映成一對多 避免記錄的重複 --> <!-- 使用extends使orders與user不用進行對映 --> <resultMap type="com.undergrowth.mybatis.po.OrdersUserDetailPojo" id="findOrderUserDetailResultMapId" extends="findOrdersUserByResultMapId"> <collection property="orderDetails" ofType="com.undergrowth.mybatis.po.OrderDetail"> <result column="orders_id" property="orders_id" /> <result column="items_id" property="items_id" /> <result column="items_num" property="items_num" /> </collection> </resultMap> <select id="findOrderUserDetailResultMap" resultMap="findOrderUserDetailResultMapId"> SELECT orders.*, user.username, user.birthday, orderdetail.orders_id, orderdetail.items_id, orderdetail.items_num FROM orders, user, orderdetail WHERE orders.user_id = user.id AND orders.id = orderdetail.orders_id </select> <resultMap type="com.undergrowth.mybatis.po.UserToOrdersVo" id="findUserAndItemsResultMapId"> <result column="user_id" property="id" /> <result column="username" property="username" /> <result column="birthday" property="birthday" /> <result column="sex" property="sex" /> <result column="user_address" property="address" /> <!-- 關聯訂單列表 --> <collection property="orderList" ofType="com.undergrowth.mybatis.po.OrdersToOrderDetailVo"> <result column="id" property="id" /> <result column="user_id" property="user_id" /> <result column="number" property="number" /> <result column="createtime" property="createtime" /> <result column="note" property="note" /> <!-- 訂單關聯明細 --> <collection property="orderDetailList" ofType="com.undergrowth.mybatis.po.OrderDetailToItems"> <result column="orders_id" property="orders_id" /> <result column="items_id" property="items_id" /> <result column="items_num" property="items_num" /> <!-- 關聯商品 --> <association property="items" javaType="com.undergrowth.mybatis.po.Items"> <result column="name" property="name" /> <result column="price" property="price" /> <result column="detail" property="detail" /> </association> </collection> </collection> </resultMap> <!-- 使用 collection和association進行使用者和商品明細的多對多的對映 --> <select id="findUserAndItemsResultMap" resultMap="findUserAndItemsResultMapId"> SELECT orders.*, user.username, user.birthday, user.sex, user.address user_address, orderdetail.orders_id, orderdetail.items_id, orderdetail.items_num, items.name, items.price, items.detail FROM orders, user, orderdetail, items WHERE orders.user_id = user.id AND orders.id = orderdetail.orders_id AND orderdetail.items_id = items.id </select> <select id="findUserById" resultType="com.undergrowth.mybatis.po.User"> select * from user where id=#{value} </select> <!-- 延時載入 association --> <resultMap type="com.undergrowth.mybatis.po.OrdersUserPojo" id="findOrderUserLazyLoadingId"> <result column="id" property="id" /> <result column="user_id" property="user_id" /> <result column="number" property="number" /> <result column="createtime" property="createtime" /> <result column="note" property="note" /> <association property="user" javaType="com.undergrowth.mybatis.po.User" select="findUserById" column="user_id"></association> </resultMap> <select id="findOrderUserLazyLoading" resultMap="findOrderUserLazyLoadingId"> select * from orders </select> <!-- 開啟Mapper的二級快取 預設實現為PerpetualCache --> <cache></cache> </mapper>
介面檔案
package com.undergrowth.mybatis.mapper; import java.util.List; import com.undergrowth.mybatis.po.OrdersUser; import com.undergrowth.mybatis.po.OrdersUserDetailPojo; import com.undergrowth.mybatis.po.OrdersUserPojo; import com.undergrowth.mybatis.po.UserToOrdersVo; /** * 通過 * @author u1 * */ public interface OrderUserMapper { public List<OrdersUser> findOrdersUserByResultType(); public List<OrdersUserPojo> findOrdersUserByResultMap(); public List<OrdersUserDetailPojo> findOrderUserDetailResultMap(); public List<UserToOrdersVo> findUserAndItemsResultMap(); public List<OrdersUserPojo> findOrderUserLazyLoading(); }
測試程式碼
package com.undergrowth.mybatis.dao;
import java.io.IOException;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.Before;
import org.junit.Test;
import com.undergrowth.mybatis.mapper.OrderUserMapper;
import com.undergrowth.mybatis.po.OrdersUser;
import com.undergrowth.mybatis.po.OrdersUserDetailPojo;
import com.undergrowth.mybatis.po.OrdersUserPojo;
import com.undergrowth.mybatis.po.UserToOrdersVo;
import com.undergrowth.mybatis.util.SqlSessionUtil;
/**
* 測試程式碼
* resuType--將sql的列名和pojo的屬性進行一一的對映
* resultMap--可以避免使用resultType方式的重複記錄
* association--將sql列對映到pojo物件中 collection--將關聯資訊對映到list列表中
* association、collection都具備延時載入功能
* mybatis具有二級快取
* SqlSession--一級快取，當SqlSession未關閉時，使用key-value的形式儲存物件
* Mapper名稱空間--二級快取，二級快取的介面為Cache
* ，mybatis提供的二級快取預設實現為PerpetualCache，以Mapper的名稱空間為單位進行快取，可跨多個SqlSession
* 要進行二級快取的物件必須序列化
* @author u1
*
*/
public class OrderUserMapperDao {
SqlSessionFactory sqlSessionFactory = null;
@Before
public void before() throws IOException {
sqlSessionFactory = SqlSessionUtil
.getSqlSessionFactory("mybatis-conf.xml");
}
/**
* 使用resultType進行一對一的對映
*/
@Test
public void testOneToOne() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
OrderUserMapper orderUserMapper = sqlSession
.getMapper(OrderUserMapper.class);
List<OrdersUser> ordersUsers = orderUserMapper
.findOrdersUserByResultType();
for (OrdersUser ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
sqlSession.close();
}
}
/**
* 使用resultMap進行一對一的對映
*/
@Test
public void testOneToOneResultMap() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
OrderUserMapper orderUserMapper = sqlSession
.getMapper(OrderUserMapper.class);
List<OrdersUserPojo> ordersUsers = orderUserMapper
.findOrdersUserByResultMap();
for (OrdersUserPojo ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
sqlSession.close();
}
}
/**
* 使用resultMap和collection進行一對多的對映
*/
@Test
public void findOrderUserDetailResultMap() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
OrderUserMapper orderUserMapper = sqlSession
.getMapper(OrderUserMapper.class);
List<OrdersUserDetailPojo> ordersUsers = orderUserMapper
.findOrderUserDetailResultMap();
for (OrdersUserDetailPojo ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
sqlSession.close();
}
}
/**
* 使用resultMap和collection association進行多對多的對映
*/
@Test
public void findUserAndItemsResultMap() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
OrderUserMapper orderUserMapper = sqlSession
.getMapper(OrderUserMapper.class);
List<UserToOrdersVo> ordersUsers = orderUserMapper
.findUserAndItemsResultMap();
for (UserToOrdersVo ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
sqlSession.close();
}
}
/**
* 延時載入
*/
@Test
public void findOrderUserLazyLoading() {
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
OrderUserMapper orderUserMapper = sqlSession
.getMapper(OrderUserMapper.class);
List<OrdersUserPojo> ordersUsers = orderUserMapper
.findOrderUserLazyLoading();
for (OrdersUserPojo ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
sqlSession.close();
}
}
/**
* 測試二級快取
* @throws IOException
*/
@Test
public void testCache() throws IOException{
SqlSession sqlSession=SqlSessionUtil.getSqlSessionFactory("mybatis-conf.xml").openSession();
OrderUserMapper mapper=sqlSession.getMapper(OrderUserMapper.class);
System.out.println("第一次查詢訂單使用者");
List<OrdersUser> ordersUsers=mapper.findOrdersUserByResultType();
for (OrdersUser ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
//關閉一級快取
sqlSession.close();
//如果未使用二級快取 此時再次查詢 會輸出查詢語句
sqlSession=SqlSessionUtil.getSqlSessionFactory("mybatis-conf.xml").openSession();
mapper=sqlSession.getMapper(OrderUserMapper.class);
System.out.println("第二次查詢");
ordersUsers=mapper.findOrdersUserByResultType();
for (OrdersUser ordersUser : ordersUsers) {
System.out.println(ordersUser);
}
sqlSession.close();
}
}
開快取和延時載入配置
<!-- mybatis執行時全域性引數配置 -->
<settings>
<setting name="cacheEnabled" value="true"></setting>
<setting name="lazyLoadingEnabled" value="true" />
<!-- 按需載入每個懶載入屬性 -->
<setting name="aggressiveLazyLoading" value="false" />
</settings>剩下的除了和前一篇部落格一樣外 還有一些POJO
package com.undergrowth.mybatis.po;
import java.io.Serializable;
import java.util.Date;
public class OrdersUser extends Orders implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private String username;
private Date birthday;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return super.toString() + "[username=" + username + ", birthday="
+ birthday + "]";
}
}
package com.undergrowth.mybatis.po;
public class OrdersUserPojo extends Orders {
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@Override
public String toString() {
return super.toString() + "OrdersUserPojo [user=" + user + "]";
}
}
package com.undergrowth.mybatis.po;
import java.util.List;
public class UserToOrdersVo extends User {
private List<OrdersToOrderDetailVo> orderList;
public List<OrdersToOrderDetailVo> getOrderList() {
return orderList;
}
public void setOrderList(List<OrdersToOrderDetailVo> orderList) {
this.orderList = orderList;
}
@Override
public String toString() {
return super.toString()+"UserToOrdersVo [orderList=" + orderList + "]";
}
}
package com.undergrowth.mybatis.po;
import java.util.List;
public class OrdersToOrderDetailVo extends Orders {
private List<OrderDetailToItems> orderDetailList;
public List<OrderDetailToItems> getOrderDetailList() {
return orderDetailList;
}
public void setOrderDetailList(List<OrderDetailToItems> orderDetailList) {
this.orderDetailList = orderDetailList;
}
@Override
public String toString() {
return super.toString() + "OrdersToOrderDetailVo [orderDetailList="
+ orderDetailList + "]";
}
}
package com.undergrowth.mybatis.po;
public class OrderDetailToItems extends OrderDetail {
private Items items;
public Items getItems() {
return items;
}
public void setItems(Items items) {
this.items = items;
}
@Override
public String toString() {
return super.toString() + "OrderDetailToItems [items=" + items + "]";
}
}