MyBatis一對一、一對多、多對多級聯查詢
阿新 • • 發佈：2018-12-16
0.準備工作：
1.引入maven依賴：其中包括mybatis本身和逆向工程生成依賴
<dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.11</version> <scope>test</scope> </dependency> <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis --> <!--Mybatis--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.6</version> </dependency> <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --> <!--Mysql的驅動--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.13</version> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core --> <!--log4j日誌的兩個核心jar--> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>2.11.1</version> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-api --> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>2.11.1</version> </dependency> <!-- https://mvnrepository.com/artifact/org.mybatis.generator/mybatis-generator-core --> <!--Mybatis工程逆向生成--> <dependency> <groupId>org.mybatis.generator</groupId> <artifactId>mybatis-generator-core</artifactId> <version>1.3.5</version> </dependency> </dependencies> <build> <finalName>mybatisTestDay1_2</finalName> <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) --> <plugins> <!--Mybatis-generator外掛,用於自動生成Mapper和POJO--> <plugin> <groupId>org.mybatis.generator</groupId> <artifactId>mybatis-generator-maven-plugin</artifactId> <version>1.3.2</version> <configuration> <!--配置檔案的位置--> <configurationFile>src/main/resources/generatorConfig.xml</configurationFile> <verbose>true</verbose> <overwrite>true</overwrite> </configuration> <executions> <execution> <id>Generate MyBatis Artifacts</id> <goals> <goal>generate</goal> </goals> </execution> </executions> </plugin> </plugins> </pluginManagement> </build>
2.如果想在使用過程中檢視日誌輸出，需要在resources中新增log4j的配置檔案
<?xml version="1.0" encoding="UTF-8"?> <Configuration status="warn"> <Appenders> <Console name="Console" target="SYSTEM_OUT"> <PatternLayout pattern="%m%n" /> </Console> </Appenders> <Loggers> <Root level="INFO"> <AppenderRef ref="Console" /> </Root> </Loggers> </Configuration>
3.關於逆向工程生成，可以看我另一篇博文
4.逆向生成好實體類、實體類的mapper對映檔案之後，寫mybatis配置檔案
<?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> <!-- 1、mybatis也可以使用properties來引入外部properties配置檔案的內容（主要還是配置資料庫賬號密碼） resource 引入類路徑下資源 url 引入網路路徑或磁碟路徑下資源 --> <properties resource="dbConfig.properties"></properties> <!-- 2、settings包含很多重要的全域性引數設定，一般使用預設即可 setting標識具體的設定項 name表示設定項的名字 value表示設定項的值 --> <settings> <!--設定開啟懶載入--> <setting name="lazyLoadingEnabled" value="true"/> <setting name="aggressiveLazyLoading" value="false"/> <setting name="cacheEnabled" value="true"/> </settings> <!-- 3、typeAliases 為java型別起別名，在parameterType和resultType中就可以直接使用別名了 typeAlias 為某個具體的java型別取別名 type java類的全類名，預設別名就是類名小寫 alias 自定義別名 --> <typeAliases> <typeAlias type="com.ogms.domain.User" alias="User" /> <!-- package為某個包下面所有類批量起別名 name 表示包的名稱 預設別名為類名小寫，在使用的的時候，首字母大小寫都可以 這裡重複配置了User類，複製的時候注掉一種配置--> <!--<package name="com.ogms.domain" />--> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <!-- 配置資料庫連線資訊 --> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </dataSource> </environment> </environments> <mappers> <!--單獨載入，根目錄是資源目錄resources--> <mapper resource="mappers/UserMapper.xml"/> <mapper resource="mappers/ItemMapper.xml"/> <mapper resource="mappers/OrdersMapper.xml"/> <mapper resource="mappers/OrderdetailMapper.xml"/> <mapper resource="mappers/OrdersUserMapper.xml"/> <mapper resource="mappers/UserItemVoMapper.xml"/> <mapper resource="mappers/OrdersUserLazyLoadingMapper.xml"/> <!--批量載入，根目錄是類的根目錄java，即將UserMapper.xml放在com.ogms.configs下--> <!--<package name="com.ogms.configs"></package>--> </mappers> </configuration>
5.獲取SqlSession的類：
package com.ogms.dao;
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 java.io.IOException;
import java.io.InputStream;
/**
* @Author: David.Xiao
* @Date: 2018/11/17 15:52
* @Description:
*/
public class MybatisUtils {
static String resource = "mybatisConfig.xml";
static SqlSessionFactory sqlSessionFactory;
static SqlSession session;
static InputStream inputStream;
static {
try {
inputStream = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
//建立Session工廠，用以產生session
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//得到session
session = sqlSessionFactory.openSession();
}
public static SqlSession getSqlSession()
{
return session;
}
}
6.一個訂單隻對應一個使用者，一對一查詢對映檔案及測試程式碼：
首先在Orders類中新增User物件
public class Orders {
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
//...省略其它成員
}寫OrdersUserMapper.xml
<?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.ogms.domain.OrdersUserMapper" >
<!--對映訂單關聯的使用者-->
<resultMap id="UserOrderVoResultMap" type="com.ogms.vo.OrderUserVo" >
<id column="id" property="id" jdbcType="BIGINT" />
<result column="user_id" property="userId" jdbcType="BIGINT" />
<result column="number" property="number" jdbcType="VARCHAR" />
<result column="createtime" property="createtime" jdbcType="TIMESTAMP" />
<result column="note" property="note" jdbcType="VARCHAR" />
<result column="username" property="userName" jdbcType="VARCHAR"/>
<result column="sex" property="sex" jdbcType="CHAR"/>
<result column="address" property="address" jdbcType="VARCHAR"/>
<!--用於對映一對一關聯查詢, 一個訂單關聯一個使用者,association表示被關聯的表和java實體類之間的對映關係
property:要將關聯查詢的使用者資訊對映到Orders中哪個屬性,在此之前必須在Orders類中建立User user成員-->
<association property="user" javaType="com.ogms.domain.User">
<!--在 一個訂單隻關聯一個使用者 關聯中,column指定訂單表中唯一標識使用者的欄位-->
<id column="user_id" property="id"/>
<result column="username" property="username"/>
<result column="sex" property="sex"/>
<result column="address" property="address"/>
</association>
</resultMap>
<!--一對一查詢 對映訂單關聯的使用者-->
<select id="queryOrdersUser" resultMap="UserOrderVoResultMap">
SELECT orders.*,username,sex,address FROM orders,user where orders.user_id = user.id;
</select>
</mapper>在OrdersUserMapper介面類中新增方法：
public interface OrdersUserMapper {
List<OrderUserVo> queryOrdersUser();
}測試程式碼：
package com.ogms.dao;
import com.ogms.domain.OrdersUserMapper;
import com.ogms.vo.OrderUserVo;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* @Author: David.Xiao
* @Date: 2018/11/21 20:16
* @Description:
*/
public class One2OneTest {
@Test
public void queryOrdersUser()
{
SqlSession sqlSession = MybatisUtils.getSqlSession();
//建立UserMapper代理物件
OrdersUserMapper ordersUserMapper = sqlSession.getMapper(OrdersUserMapper.class);
List<OrderUserVo> list = ordersUserMapper.queryOrdersUser();
System.out.println(list);
}
}7.一對多對映檔案及測試程式碼
<?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.ogms.domain.UserMapper">
<!--使用二級快取-->
<cache/>
<resultMap id="BaseResultMap" type="com.ogms.domain.User">
<result column="id" jdbcType="BIGINT" property="id" />
<result column="username" jdbcType="VARCHAR" property="username" />
<result column="birthday" jdbcType="DATE" property="birthday" />
<result column="sex" jdbcType="CHAR" property="sex" />
<result column="address" jdbcType="VARCHAR" property="address" />
</resultMap>
<!--一對多對映:查詢每個使用者關聯的訂單-->
<resultMap id="UserOrderResultMap" type="com.ogms.domain.User">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="birthday" property="birthday"/>
<result column="sex" property="sex"/>
<result column="address" property="address"/>
<collection property="ordersList" ofType="com.ogms.domain.Orders">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="number" property="number"/>
<result column="createtime" property="createtime"/>
<result column="note" property="note"/>
</collection>
</resultMap>
<!--一對多查詢:查詢每個使用者關聯的訂單-->
<select id="queryUserOrder" resultMap="UserOrderResultMap">
select user.*,user_id,number,createtime,note from user,orders where user.id = orders.user_id;
</select>
<select id="queryUserById" parameterType="int" resultMap="BaseResultMap">
select user.* from user where id = #{user_id};
</select>
</mapper>在User實體類中新增OrderList成員
public class User {
private List<Orders> ordersList;
public List<Orders> getOrdersList() {
return ordersList;
}
public void setOrdersList(List<Orders> ordersList) {
this.ordersList = ordersList;
}
//省略其它成員
}UserMapper介面類：
public interface UserMapper {
List<User> queryUserOrder();
User queryUserById(int user_id);
}測試程式碼：
package com.ogms.dao;
import com.ogms.domain.User;
import com.ogms.domain.UserMapper;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* @Author: David.Xiao
* @Date: 2018/11/22 14:47
* @Description:
*/
public class One2ManyTest {
/**
* 一對多：查詢一個使用者關聯的訂單
*/
@Test
public void queryUserOrders()
{
SqlSession sqlSession = MybatisUtils.getSqlSession();
//建立UserMapper代理物件
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
List<User> userList = userMapper.queryUserOrder();
System.out.println(userList);
}
}8.一個使用者關聯多個商品，一個商品也被多個使用者購買，多對多操作
建立一個UserItem實體類，其中包含要查詢出各個表中的欄位對應的成員
public class UserItemVo {
private int id;
private String username;
private String address;
private int order_id;
private String order_number;
private Date order_createtime;
private int item_id;
private int orderdetail_num;
private String item_name;
private Float item_price;
}對映檔案：
<?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" >
<mapper namespace="com.ogms.domain.UserItemVoMapper" >
<!--對映訂單關聯的使用者-->
<resultMap id="UserItemVoResultMap" type="com.ogms.vo.UserItemVo" >
<id column="id" property="id" jdbcType="BIGINT" />
<result column="username" property="username"/>
<result column="address" property="address"/>
<result column="order_id" property="order_id"/>
<result column="number" property="order_number"/>
<result column="order_createtime" property="order_createtime"/>
<result column="item_id" property="item_id"/>
<result column="item_num" property="orderdetail_num"/>
<result column="name" property="item_name"/>
<result column="price" property="item_price"/>
</resultMap>
<!--多對多查詢 對映訂單關聯的使用者-->
<select id="queryUserItems" resultMap="UserItemVoResultMap">
SELECT user.id,username,address,orders.id order_id,number,orders.createtime order_createtime,item.id item_id,item_num,name,price FROM orders,user,orderdetail,item
where orders.user_id = user.id and orderdetail.order_id = orders.id and item.id = orderdetail.item_id;
</select>
</mapper>介面類：
public interface UserItemVoMapper {
List<UserItemVo> queryUserItems();
}測試程式碼：
public class Many2ManyTest {
/**
* 多對多：查詢一個使用者關聯的訂單
*/
@Test
public void queryUserOrders()
{
SqlSession sqlSession = MybatisUtils.getSqlSession();
//建立UserMapper代理物件
UserItemVoMapper userItemVoMapper = sqlSession.getMapper(UserItemVoMapper.class);
List<UserItemVo> userList = userItemVoMapper.queryUserItems();
for (UserItemVo useritem:userList) {
System.out.println(useritem);
}
}
}