Mybatis级联查询
Posted 虚极静笃
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转自:http://blog.csdn.net/yulei_qq/article/details/22039815
工程的目录结构:
有两个表,一个文章表article ,一个用户表user。
- create table article (id int(11) not null auto_increment,
- userid int(11) not null,
- title varchar(100) not null,
- content text not null,
- primary key (id))ENGINE=InnoDB DEFAULT CHARSET=utf8;
- insert into article(id,userid,title,content) values(1,1,‘test_title‘,‘text_content‘);
- insert into article(id,userid,title,content) values(2,1,‘test_title_2‘,‘text_content_2‘);
- insert into article(id,userid,title,content) values(3,1,‘test_title_3‘,‘text_content_3‘);
- insert into article(id,userid,title,content) values(4,1,‘test_title_4‘,‘text_content_4‘);
- create table user (id int(11) not null auto_increment,
- userName varchar(50) default null,
- userAge int(11) default null,
- userAddress varchar(200) default null,
- primary key(id)) ENGINE=InnoDB DEFAULT CHARSET=utf8;
- insert into user(id,userName,userAge,userAddress) values(1,‘summer‘,‘100‘,‘上海‘);
现在要查询,根据用户的ID来查询他所拥有的文章。那么需要编写SQL语句如下:
- select a.id, a.userName ,a.userAddress ,b.id aid, b.title,b.content
- from user a,article b
- where a.id=b.userid and a.id=#{id}
现在就来贴下相关的JAVA代码和映射文件吧,该说的都在注释里了。
User.java
- package com.mybatis.model;
- public class User {
- private int id;
- private String userName;
- private String userAge;
- private String userAddress;
- public int getId() {
- return id;
- }
- public void setId(int id) {
- this.id = id;
- }
- public String getUserName() {
- return userName;
- }
- public void setUserName(String userName) {
- this.userName = userName;
- }
- public String getUserAge() {
- return userAge;
- }
- public void setUserAge(String userAge) {
- this.userAge = userAge;
- }
- public String getUserAddress() {
- return userAddress;
- }
- public void setUserAddress(String userAddress) {
- this.userAddress = userAddress;
- }
- }
Article.java
- package com.mybatis.model;
- public class Article {
- private int id;
- private User user; //文章的用户定义一个User对象,而不是int 类型
- private String title;
- private String content;
- public int getId() {
- return id;
- }
- public void setId(int id) {
- this.id = id;
- }
- public User getUser() {
- return user;
- }
- public void setUser(User user) {
- this.user = user;
- }
- public String getTitle() {
- return title;
- }
- public void setTitle(String title) {
- this.title = title;
- }
- public String getContent() {
- return content;
- }
- public void setContent(String content) {
- this.content = content;
- }
- }
接口类
IUserDao.java
- package com.mybatis.dao;
- import java.util.List;
- import com.mybatis.model.Article;
- public interface IUserDao {
- public List<Article> getUserArticles(int id);
- }
总配置文件configution.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>
- <!-- 给实体类去一个别名 -->
- <typeAlias type="com.mybatis.model.User" alias="User"/>
- <typeAlias type="com.mybatis.model.Article" alias="Article"/>
- </typeAliases>
- <!-- 数据源配置,这里用mysql数据库 -->
- <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://127.0.0.1:3306/test"/>
- <property name="username" value="root"/>
- <property name="password" value="123456"/>
- </dataSource>
- </environment>
- </environments>
- <mappers>
- <!-- book.xml装载进来,等同于把Dao的实现类装载进来 -->
- <mapper resource="com/mybatis/model/User.xml"/>
- </mappers>
- </configuration>
User.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.mybatis.dao.IUserDao">
- <!-- User联合Article进行查询 (多对一的方式)-->
- <resultMap type="Article" id="resultUserArticleList">
- <id property="id" column="aid"/>
- <result property="title" column="title"/>
- <result property="content" column="content"/>
- <!--关联一个用户 ,如果是关联多个的话,就需要用collection了-->
- <association property="user" javaType="User"> <!-- 这个 property="user" 对应的是Article中的User user属性-->
- <id property="id" column="id"/>
- <result property="userName" column="userName"/>
- <result property="userAddress" column="userAddress"/>
- </association>
- </resultMap>
- <select id="getUserArticles" parameterType="int" resultMap="resultUserArticleList">
- select a.id, a.userName ,a.userAddress ,b.id aid, b.title,b.content
- from user a,article b
- where a.id=b.userid and a.id=#{id}
- </select>
- </mapper>
总后,编写个测试类.
- package com.mybatis.test;
- import java.io.IOException;
- 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.mybatis.dao.IUserDao;
- import com.mybatis.model.Article;
- public class Test {
- /***
- * 获得MyBatis SqlSessionFactory
- * SqlSessionFactory 负责创建SqlSession ,一旦创建成功,就可以用SqlSession实例来执行映射语句
- * ,commit,rollback,close等方法
- * @return
- */
- private static SqlSessionFactory getSessionFactory(){
- SqlSessionFactory sessionFactory=null;
- String resource="configuration.xml";
- try {
- sessionFactory=new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader(resource));
- } catch (IOException e) {
- e.printStackTrace();
- }
- return sessionFactory;
- }
- /**
- * main 方法
- * @param args
- */
- public static void main(String[] args) {
- SqlSession session=getSessionFactory().openSession();
- try {
- IUserDao userDao=session.getMapper(IUserDao.class);
- //传入用户的id=1
- List<Article> listArticle=userDao.getUserArticles(1);
- for(Article article:listArticle){
- System.out.println(article.getTitle()+":"+article.getContent()+
- ":作者是:"+article.getUser().getUserName()+":地址:"+
- article.getUser().getUserAddress());
- }
- } catch (Exception e) {
- e.printStackTrace();
- }
- finally{
- session.close();
- }
- }
- }
运行后结果如下:
- test_title:text_content:作者是:summer:地址:上海
- test_title_2:text_content_2:作者是:summer:地址:上海
- test_title_3:text_content_3:作者是:summer:地址:上海
- test_title_4:text_content_4:作者是:summer:地址:上海
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