利用SSM(springmvc+spring+mybatis)实现多表联合查询

一、数据库

Author表 （authorid主键） NewsInfo表（newsno主键） NewsType表（news_typeid主键）

二、实体类

Author类

package com.neusoft.po;

import java.util.List;

/**
 * 新闻类别类
 * @author hyc
 *
 */
public class NewsType {
	private  int news_typeid;//类别编号
	private String news_typename;//类别名称
	
	//一对多的关系
    private List<NewsInfo> infoList;
    
	public List<NewsInfo> getInfoList() {
		return infoList;
	}
	public void setInfoList(List<NewsInfo> infoList) {
		this.infoList = infoList;
	}
	public NewsType() {
		super();
	}
	
	public NewsType(int news_typeid, String news_typename,
			List<NewsInfo> infoList) {
		super();
		this.news_typeid = news_typeid;
		this.news_typename = news_typename;
		this.infoList = infoList;
	}
	public int getNews_typeid() {
		return news_typeid;
	}
	public void setNews_typeid(int news_typeid) {
		this.news_typeid = news_typeid;
	}
	public String getNews_typename() {
		return news_typename;
	}
	public void setNews_typename(String news_typename) {
		this.news_typename = news_typename;
	}
	
	
	
	
}

三、Mapper

<resultMap type="com.neusoft.po.NewsInfo" id="newsInfoMap">
	    <id column="newsno" property="newsno" />
	    <result column="news_title" property="news_title"/>
    
	   <association property="author" javaType="com.neusoft.po.Author">
		<result column="authorname" property="authorname"/>
	   </association>
	   
	   <association property="type" javaType="com.neusoft.po.NewsType">
	    <result column="news_typename" property="news_typename"/>
	   </association>
</resultMap>

<select id="findnewsInfoMap" resultMap="newsInfoMap">
select i.newsno,i.news_title,a.authorname,t.news_typename from news_info i,news_author a,news_type t where i.news_author=a.authorid and i.news_type=t.news_typeid   
</select>

NewsInfoMapper.xml

package com.neusoft.mapper;

import java.util.List;

import com.neusoft.po.Author;
import com.neusoft.po.NewsInfo;
import com.neusoft.po.NewsType;

public interface NewsInfoMapper {
    /* public void insertAuthor(Author author);
     public void deleteAuthor(String authorid);
     
     
     public void insertNewsType(NewsType newsType);
     public void deleteType(int news_typeid);
     
     
     public void insertNewsInfo(NewsInfo newsInfo);
     public void deleteInfo(String userno);*/
     public List<NewsInfo> findnewsInfoMap();
} 
NewsInfoMapper.java
 

 
四、service

  
 package com.neusoft.service;

import java.util.List;

import org.springframework.stereotype.Service;

import com.neusoft.po.Author;
import com.neusoft.po.NewsInfo;
import com.neusoft.po.NewsType;


public interface NewsInfoService {
   
    public List<NewsInfo> allNewsInfo();
}NewsInfoService.java



 @Autowired
	NewsInfoMapper newsInfoMapper;
	@Override
	public List<NewsInfo> allNewsInfo() {
		List<NewsInfo> newsInfoList=new ArrayList<NewsInfo>();
		newsInfoList=newsInfoMapper.findnewsInfoMap();
		return newsInfoList;
	} NewsInfoServiceImpl.java 五、control @Autowired
	NewsInfoService newsInfoService;
	@RequestMapping("searchInfo")
	 public String searchNewsInfo(Model model){
		List<NewsInfo> newsList = newsInfoService.allNewsInfo();
		model.addAttribute("newsList", newsList);
		return "show";
	 }  NewsInfoController.java

 六、jsp

 <a href="searchInfo.action">查询Info</a>    ----index.jsp(我的首页) <c:forEach items="${newsList}" var="newsList">
     ${newsList.newsno}<br>
     ${newsList.news_title}<br>
   </c:forEach>-------show.jsp（利用EL表达式，forEach循环 表示查询的结果。注意不要忘记在jsp头部写下taglib引用c标签） 
七、总结
 

 
 多表查询主要是考究表与表之间的关系，这里我用的是三表查询；三表分别为：Author、NewsInfo、NewsType Author  :   NewsInfo  =  1  :  1 NewsType : NewsInfo = 1 : N 记住在po层里的NewsType声明一对多的关系时，别忘记在NewsInfo里声明多对一的关系 //一对多的关系（NewsType里写的）
    private List<NewsInfo> infoList; 
//NewsInfo里写的
 
 private NewsType type;
    private Author author;