Mybatis关联查询(嵌套查询).docx

Mybatis关联查询（嵌套查询）表的存储sql文件： 表的存储sql文件： select user.id user_id,user.userName user_userName,user.userAddress user_userAddress, article.id article_id,article.title article_title,article.content article_content from user,article where user.id=article.userid and user.id=#id !- select * from user where id = #id - Blog.xml配置： select user.id user_id,user.userName user_userName,user.userAddress user_userAddress, article.id article_id,article.title article_title,article.content article_content, blog.id blog_id, blog.title blog_title from user,article,blog where user.id=article.userid and blog.id=article.blogid and blog.id=#id IArticleOperation定义：package com.mybatis.test;import java.util.List;public interface IArticleOperation public List getUserArticles(int userID);IBlogOperation定义：package com.mybatis.test;public interface IBlogOperation Blog getBlogByID(int id); Test类：package com.mybatis.test;import java.io.Reader;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;public class Test private static SqlSessionFactory sqlSessionFactory; private static Reader reader; static try /通过配置文件初始化sqlSessionFactory reader = Resources.getResourceAsReader(Configuration.xml); sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader); catch (Exception e) e.printStackTrace(); public static SqlSessionFactory getSession() return sqlSessionFactory; public void getUserByID(int userID) SqlSession session = sqlSessionFactory.openSession(); try IUserOperation userOperation = session .getMapper(IUserOperation.class); User user = userOperation.selectUserByID(userID); if (user != null) System.out.println(user.getId() + : + user.getUserName() + : + user.getUserAddress(); finally session.close(); public void getUserList(String userName) SqlSession session = sqlSessionFactory.openSession(); try IUserOperation userOperation = session .getMapper(IUserOperation.class); List users = userOperation.selectUsersByName(userName); for (User user : users) System.out.println(user.getId() + : + user.getUserName() + : + user.getUserAddress(); finally session.close(); /* * 增加后要commit */ public void addUser() User user = new User(); user.setUserAddress(place); user.setUserName(test_add); user.setUserAge(30); SqlSession session = sqlSessionFactory.openSession(); try IUserOperation userOperation = session .getMapper(IUserOperation.class); userOperation.addUser(user); mit(); System.out.println(新增用户ID： + user.getId(); finally session.close(); /* * 修改后要commit */ public void updateUser() SqlSession session = sqlSessionFactory.openSession(); try IUserOperation userOperation = session .getMapper(IUserOperation.class); User user = userOperation.selectUserByID(1); if (user != null) user.setUserAddress(A new place); userOperation.updateUser(user); mit(); finally session.close(); /* * 删除后要commit. * * param id */ public void deleteUser(int id) SqlSession session = sqlSessionFactory.openSession(); try IUserOperation userOperation = session .getMapper(IUserOperation.class); userOperation.deleteUser(id); mit(); finally session.close(); public void getUserArticles(int userid) SqlSession session = sqlSessionFactory.openSession(); try IArticleOperation articleOperation = session .getMapper(IArticleOperation.class); List articles = articleOperation.getUserArticles(userid); for (Article article : articles) System.out.println(article.getTitle() + : + article.getContent() + 用户名： + article.getUser().getUserName() + 用户地址： + article.getUser().getUserAddress(); finally session.close(); public void getBlogArticles(int blogid) SqlSession session = sqlSessionFactory.openSession(); try IBlogOperation blogOperation = session .getMapper(IBlogOperation.class); Blog blog = blogOperation.getBlogByID(blogid); System.out.println(blog.getTitle() + :); List articles = blog.getArticles(); for (Article article : articles) System.out.println(article.getTitle() + : + article.getContent() + 用户名： + article.getUser().getUserName() + 用户地址： + article.getUser().getUserAddress(); /*System.out.println(article.getTitle() + : + article.getContent();*/ finally session.close(); public static void main(String args) try Test test = new Test(); / test.getUserByID(1); / test.getUserList(test1); / test.addUser(); / test.updateUser(); / test.deleteUser(6); /test.getUserArticles(1); test.getBlogArticles(1); catch (Exception e) System.out.println(e.getMessage(); Mybatis的“N+1查询问题” SELECT * FROM BLOG WHERE ID = #id SELECT * FROM AUTHOR WHERE ID = #id有两个查询语句：一个来加载博客，另外一个来加载作者，而且博客的结果映射描述了“selectAuthor”语句应该被用来加载它的 author 属性。其他所有的属性将会被自动加载，假设它们的列和属性名相匹配。这种方式很