為了說明這一點，我們正在考慮以下示例域模型：

會有用戶，每個用戶可能都有一個博客，每個博客可以包含零個或多個帖子。

這三個表的數據庫結構如下：

CREATE TABLE user (user_id int(10) unsigned NOT NULL auto_increment,email_id varchar(45) NOT NULL,password varchar(45) NOT NULL,first_name varchar(45) NOT NULL,last_name varchar(45) default NULL,blog_id int(10) unsigned default NULL,PRIMARY KEY (user_id),UNIQUE KEY Index_2_email_uniq (email_id),KEY FK_user_blog (blog_id),CONSTRAINT FK_user_blog FOREIGN KEY (blog_id) REFERENCES blog (blog_id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1;CREATE TABLE blog (blog_id int(10) unsigned NOT NULL auto_increment,blog_name varchar(45) NOT NULL,created_on datetime NOT NULL,PRIMARY KEY (blog_id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1;CREATE TABLE post (post_id int(10) unsigned NOT NULL auto_increment,title varchar(45) NOT NULL,content varchar(1024) NOT NULL,created_on varchar(45) NOT NULL,blog_id int(10) unsigned NOT NULL,PRIMARY KEY (post_id),KEY FK_post_blog (blog_id),CONSTRAINT FK_post_blog FOREIGN KEY (blog_id) REFERENCES blog (blog_id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1;

在這里，我將解釋如何獲取和映射*-一對一和一對多結果映射。

package com.sivalabs.mybatisdemo.domain;public class User {private Integer userId;private String emailId;private String password;private String firstName;private String lastName;private Blog blog;//setters and getters }

package com.sivalabs.mybatisdemo.domain;import java.util.ArrayList; import java.util.Date; import java.util.List;public class Blog {private Integer blogId;private String blogName;private Date createdOn;private List<Post> posts = new ArrayList<Post>();//setters and getters }

package com.sivalabs.mybatisdemo.domain;import java.util.Date;public class Post {private Integer postId;private String title;private String content;private Date createdOn;//setters and getters }

在mybatis-config.xml中，為bean配置類型別名。

<typeAliases><typeAlias type='com.sivalabs.mybatisdemo.domain.User' alias='User'/><typeAlias type='com.sivalabs.mybatisdemo.domain.Blog' alias='Blog'/><typeAlias type='com.sivalabs.mybatisdemo.domain.Post' alias='Post'/> </typeAliases>

*-具有一個結果映射：

在UserMapper.xml中，如下配置sql查詢和結果映射：

<mapper namespace='com.sivalabs.mybatisdemo.mappers.UserMapper'><resultMap type='User' id='UserResult'><id property='userId' column='user_id'/><result property='emailId' column='email_id'/><result property='password' column='password'/><result property='firstName' column='first_name'/><result property='lastName' column='last_name'/><association property='blog' resultMap='BlogResult'/></resultMap><resultMap type='Blog' id='BlogResult'><id property='blogId' column='blog_id'/><result property='blogName' column='BLOG_NAME'/><result property='createdOn' column='CREATED_ON'/> </resultMap><select id='getUserById' parameterType='int' resultMap='UserResult'>SELECT U.USER_ID, U.EMAIL_ID, U.PASSWORD, U.FIRST_NAME, U.LAST_NAME, B.BLOG_ID, B.BLOG_NAME, B.CREATED_ONFROM USER U LEFT OUTER JOIN BLOG B ON U.BLOG_ID=B.BLOG_IDWHERE U.USER_ID = #{userId}</select><select id='getAllUsers' resultMap='UserResult'>SELECT U.USER_ID, U.EMAIL_ID, U.PASSWORD, U.FIRST_NAME, U.LAST_NAME, B.BLOG_ID, B.BLOG_NAME, B.CREATED_ONFROM USER U LEFT OUTER JOIN BLOG B ON U.BLOG_ID=B.BLOG_ID</select></mapper>

在JUnit Test中，編寫一種方法來測試關聯加載。

public void getUserById() {SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();try{UserMapper userMapper = sqlSession.getMapper(UserMapper.class);User user = userMapper.getUserById(1);System.out.println(user.getBlog());}finally{sqlSession.close();} }

一對多結果映射：

在BlogMapper.xml中，如下配置Blog to Posts關系：

<mapper namespace='com.sivalabs.mybatisdemo.mappers.BlogMapper'><resultMap type='Blog' id='BlogResult'><id property='blogId' column='blog_id'/><result property='blogName' column='BLOG_NAME'/><result property='createdOn' column='CREATED_ON'/><collection property='posts' ofType='Post' resultMap='PostResult' columnPrefix='post_'></collection></resultMap><resultMap type='Post' id='PostResult'><id property='postId' column='post_id'/><result property='title' column='title'/><result property='content' column='content'/><result property='createdOn' column='created_on'/></resultMap><select id='getBlogById' parameterType='int' resultMap='BlogResult'>SELECT b.blog_id, b.blog_name, b.created_on, p.post_id as post_post_id, p.title as post_title, p.content as post_content, p.created_on as post_created_onFROM blog b left outer join post p on b.blog_id=p.blog_idWHERE b.BLOG_ID=#{blogId}</select><select id='getAllBlogs' resultMap='BlogResult'>SELECT b.blog_id, b.blog_name, b.created_on as blog_created_on, p.post_id as post_post_id, p.title as post_title, p.content as post_content, p.created_on as post_created_onFROM blog b left outer join post p on b.blog_id=p.blog_id</select></mapper>

在JUnit Test中，編寫一種測試方法來測試博客到帖子的關系映射。

public void getBlogById() {SqlSession sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();try{BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);Blog blog = blogMapper.getBlogById(1);System.out.println(blog);List<Post> posts = blog.getPosts();for (Post post : posts) {System.out.println(post);}}finally{sqlSession.close();} }

支持 整合

MyBatis-Spring是MyBatis的子項目，并提供Spring集成支持，從而大大簡化了MyBatis的用法。 對于那些熟悉Spring依賴注入方法的人來說，使用MyBatis-Spring非常簡單。

首先讓我們看看不使用Spring的MyBatis的使用過程。

1.通過傳遞包含數據源屬性，映射器XML列表和TypeAliases等的mybatis-config.xml，使用SqlSessionFactoryBuilder創建SqlSessionFactory。

2.從SqlSessionFactory創建SqlSession對象

3.從SqlSession中獲取Mapper實例并執行查詢。

4.使用SqlSession對象提交或回滾事務。

使用MyBatis-Spring，可以在Spring ApplicationContext中配置上述大多數步驟，并且可以將SqlSession或Mapper實例注入到Spring Bean中。 然后，我們可以使用Spring的TransactionManagement功能，而無需在整個代碼中編寫事務提交/回滾代碼。

現在讓我們看看如何配置MyBatis + Spring集成的東西。

步驟＃1：在pom.xml中配置MyBatis-Spring依賴項

<dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.10</version><scope>test</scope></dependency><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.1.1</version></dependency><dependency><groupId>org.mybatis</groupId><artifactId>mybatis-spring</artifactId><version>1.1.1</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-context-support</artifactId><version>3.1.1.RELEASE</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-test</artifactId><version>3.1.1.RELEASE</version><scope>test</scope></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.21</version><scope>runtime</scope></dependency><dependency><groupId>cglib</groupId><artifactId>cglib-nodep</artifactId><version>2.2.2</version></dependency>

步驟＃2：您不需要在mybatis-config.xml中配置數據庫屬性。

我們可以在Spring Container中配置DataSource并使用它來構建MyBatis SqlSessionFactory。

MyBatis-Spring使用org.mybatis.spring.SqlSessionFactoryBean代替SqlSessionFactoryBuilder來構建SqlSessionFactory。

我們可以將dataSource，Mapper XML文件位置，typeAliases等傳遞給SqlSessionFactoryBean。

<bean id='dataSource' class='org.apache.commons.dbcp.BasicDataSource'><property name='driverClassName' value='${jdbc.driverClassName}'/><property name='url' value='${jdbc.url}'/><property name='username' value='${jdbc.username}'/><property name='password' value='${jdbc.password}'/></bean><bean id='sqlSessionFactory' class='org.mybatis.spring.SqlSessionFactoryBean'><property name='dataSource' ref='dataSource' /><property name='typeAliasesPackage' value='com.sivalabs.mybatisdemo.domain'/><property name='mapperLocations' value='classpath*:com/sivalabs/mybatisdemo/mappers/**/*.xml' /></bean>

步驟＃3：配置提供ThreadSafe SqlSession對象的SqlSessionTemplate。

<bean id='sqlSession' class='org.mybatis.spring.SqlSessionTemplate'><constructor-arg index='0' ref='sqlSessionFactory' /></bean>

步驟＃4：為了能夠直接注入Mapper，我們應該注冊org.mybatis.spring.mapper.MapperScannerConfigurer并配置要在其中找到Mapper接口的包名稱。

<bean class='org.mybatis.spring.mapper.MapperScannerConfigurer'><property name='basePackage' value='com.sivalabs.mybatisdemo.mappers' /></bean>

步驟5：將 TransactionManager配置為支持基于注釋的事務支持。

<tx:annotation-driven transaction-manager='transactionManager'/><bean id='transactionManager' class='org.springframework.jdbc.datasource.DataSourceTransactionManager'><property name='dataSource' ref='dataSource' /></bean>

步驟＃6：更新Service類并在Spring容器中注冊它們。

package com.sivalabs.mybatisdemo.service;import java.util.List; import org.apache.ibatis.session.SqlSession; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional;import com.sivalabs.mybatisdemo.domain.User; import com.sivalabs.mybatisdemo.mappers.UserMapper;@Service @Transactional public class UserService {@Autowiredprivate SqlSession sqlSession; //This is to demonstrate injecting SqlSession objectpublic void insertUser(User user) {UserMapper userMapper = sqlSession.getMapper(UserMapper.class);userMapper.insertUser(user);}public User getUserById(Integer userId) {UserMapper userMapper = sqlSession.getMapper(UserMapper.class);return userMapper.getUserById(userId);}}

package com.sivalabs.mybatisdemo.service;import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional; import com.sivalabs.mybatisdemo.domain.Blog; import com.sivalabs.mybatisdemo.mappers.BlogMapper;@Service @Transactional public class BlogService {@Autowiredprivate BlogMapper blogMapper; // This is to demonstratee how to inject Mappers directlypublic void insertBlog(Blog blog) {blogMapper.insertBlog(blog);}public Blog getBlogById(Integer blogId) {return blogMapper.getBlogById(blogId);}public List<Blog> getAllBlogs() {return blogMapper.getAllBlogs();} }

注意：當我們可以直接注入Mappers時，為什么還要注入SqlSession對象？ 因為SqlSession對象包含更細粒度的方法，所以有時會派上用場。

例如：如果我們想獲取更新查詢更新了多少條記錄，可以使用SqlSession，如下所示：

int updatedRowCount = sqlSession.update('com.sivalabs.mybatisdemo.mappers.UserMapper.updateUser', user);

到目前為止，我還沒有找到一種無需使用SqlSession對象即可獲取行更新計數的方法。

步驟＃7編寫JUnit測試以測試UserService和BlogService。

package com.sivalabs.mybatisdemo;import java.util.List;import org.junit.Assert; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import com.sivalabs.mybatisdemo.domain.User; import com.sivalabs.mybatisdemo.service.UserService;@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(locations='classpath:applicationContext.xml') public class SpringUserServiceTest {@Autowiredprivate UserService userService;@Testpublic void testGetUserById() {User user = userService.getUserById(1);Assert.assertNotNull(user);System.out.println(user);System.out.println(user.getBlog());}@Testpublic void testUpdateUser() {long timestamp = System.currentTimeMillis();User user = userService.getUserById(2);user.setFirstName('TestFirstName'+timestamp);user.setLastName('TestLastName'+timestamp);userService.updateUser(user);User updatedUser = userService.getUserById(2);Assert.assertEquals(user.getFirstName(), updatedUser.getFirstName());Assert.assertEquals(user.getLastName(), updatedUser.getLastName());}}

package com.sivalabs.mybatisdemo;import java.util.Date; import java.util.List;import org.junit.Assert; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import com.sivalabs.mybatisdemo.domain.Blog; import com.sivalabs.mybatisdemo.domain.Post; import com.sivalabs.mybatisdemo.service.BlogService;@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(locations='classpath:applicationContext.xml') public class SpringBlogServiceTest {@Autowiredprivate BlogService blogService;@Testpublic void testGetBlogById() {Blog blog = blogService.getBlogById(1);Assert.assertNotNull(blog);System.out.println(blog);List<Post> posts = blog.getPosts();for (Post post : posts) {System.out.println(post);}}@Testpublic void testInsertBlog() {Blog blog = new Blog();blog.setBlogName('test_blog_'+System.currentTimeMillis());blog.setCreatedOn(new Date());blogService.insertBlog(blog);Assert.assertTrue(blog.getBlogId() != 0);Blog createdBlog = blogService.getBlogById(blog.getBlogId());Assert.assertNotNull(createdBlog);Assert.assertEquals(blog.getBlogName(), createdBlog.getBlogName());}}

參考： MyBatis教程：第3部分-映射關系 ， ? MyBatis教程：第4部分–來自JCG合作伙伴 Siva Reddy的Spring Integration，來自My Experiments on Technology博客。

翻譯自: https://www.javacodegeeks.com/2012/11/mybatis-tutorial-crud-operations-and-mapping-relationships-part-2.html

總結

以上是生活随笔為你收集整理的MyBatis教程– CRUD操作和映射关系–第2部分的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。