mybatis关联查询问题(一对多、多对一)

package com.foo.Test; import java.io.IOException; import java.io.InputStream; import java.math.BigDecimal; 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 org.json.JSONObject; import com.foo.bean.Author; import com.foo.bean.Blog; import com.foo.bean.BlogInfo; public class Test { public static SqlSessionFactory sqlSessionFactory; static{ String resource = "mybatis-config.xml"; InputStream inputStream; try { inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void main(String[] args) throws IOException { String blogId = "1"; //Test.ordinaryQueryOnTest(blogId); Test.nestedQueryOnTest(blogId); } public static void nestedOnResultTest() { SqlSession session = sqlSessionFactory.openSession(); List list = session.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo"); System.out.println("--------------------------"); System.out.println("共检索出："+list.size()+" 条数据。"); BlogInfo blog = (BlogInfo)list.get(0); System.out.println(blog.getTitle()); System.out.println("作者是："+blog.getAuthor().getUserName()); System.out.println("该博客文章总数为：" +blog.getPosts().size()); session.close(); } /* * 通过blogId获取BlogInfo对象 */ public static BlogInfo ordinaryQueryOnTest(String blogId) { BigDecimal id = new BigDecimal(blogId); SqlSession session = sqlSessionFactory.openSession(); BlogInfo blogInfo = new BlogInfo(); //1.根据blogid 查询Blog对象，将值设置到blogInfo中 Blog blog = (Blog)session.selectOne("com.foo.bean.BlogMapper.selectByPrimaryKey",id); blogInfo.setBlogId(blog.getBlogId()); blogInfo.setTitle(blog.getTitle()); //2.根据Blog中的authorId，进入数据库查询Author信息，将结果设置到blogInfo对象中 Author author = (Author)session.selectOne("com.foo.bean.AuthorMapper.selectByPrimaryKey",blog.getAuthorId()); blogInfo.setAuthor(author); //3.查询posts对象，设置进blogInfo中 List posts = session.selectList("com.foo.bean.PostMapper.selectByBlogId",blog.getBlogId()); blogInfo.setPosts(posts); //以JSON字符串的形式将对象打印出来 JSONObject object = new JSONObject(blogInfo); System.out.println(object.toString()); return blogInfo; } /* * 通过blogId获取BlogInfo对象 */ public static BlogInfo nestedQueryOnTest(String blogId) { BigDecimal id = new BigDecimal(blogId); SqlSession session = sqlSessionFactory.openSession(); BlogInfo blogInfo = new BlogInfo(); blogInfo = (BlogInfo)session.selectOne("com.foo.bean.BlogMapper.queryBlogInfoById",id); JSONObject object = new JSONObject(blogInfo); System.out.println(object.toString()); return blogInfo; } /* * 获取所有Blog的所有信息 */ public static BlogInfo nestedResultOnTest(String blogId) { BigDecimal id = new BigDecimal(blogId); SqlSession session = sqlSessionFactory.openSession(); BlogInfo blogInfo = new BlogInfo(); blogInfo = (BlogInfo)session.selectOne("com.foo.bean.BlogMapper.queryAllBlogInfo",id); JSONObject object = new JSONObject(blogInfo); System.out.println(object.toString()); return blogInfo; } }