ibatis多对一表联系关系映射的解决过程

ibatis多对一表关联映射的解决过程
1、问题：当查询新闻的时候我们一般情况下需要新闻的类型以及作者的信息。根据表设计的规范我们要把文章，文章类型，作者信息分别设计成一张表，其中文章中分别存在指向文章类型和作者信息的外键。我们的问题就是怎么使用ibatis把表空间数据映射为java的实体类属性。

2、表DDL，
用户表
CREATE TABLE `users` (
`id` int(11) NOT NULL auto_increment,
`username` varchar(25) default NULL,
’password` varchar(32) default NULL,
`gender` int(11) default '1',
`birth` date default NULL,
`user_type` int(11) default NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

文章类型表
CREATE TABLE `article_class` (
`acid` int(11) NOT NULL auto_increment,
`name` varchar(25) default NULL,
`class_desc` varchar(255) default NULL,
PRIMARY KEY (`acid`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

文章表
CREATE TABLE `article` (
`aid` int(11) NOT NULL auto_increment,
`title` varchar(36) default NULL,
`content` text,
`classid` int(11) default NULL,
`userid` int(11) default NULL,
PRIMARY KEY (`aid`),
KEY `classid` (`classid`),
KEY `userid` (`userid`),
CONSTRAINT `article_ibfk_1` FOREIGN KEY (`classid`) REFERENCES `article_class` (`acid`),
CONSTRAINT `article_ibfk_2` FOREIGN KEY (`userid`) REFERENCES `users` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

3、实体类

   import java.sql.Date;public class User {private Integer id;private String username;private String password;private int gender;private Date birth;private int userType = 1;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getGender() {return gender;}public void setGender(int gender) {this.gender = gender;}public Date getBirth() {return birth;}public void setBirth(Date birth) {this.birth = birth;}public int getUserType() {return userType;}public void setUserType(int user_type) {this.userType = user_type;}}文章类型类public class ArticleClass {private Integer id;private String name;private String desc;public ArticleClass() {}public ArticleClass(int id) {this.id = id;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getDesc() {return desc;}public void setDesc(String desc) {this.desc = desc;}}文章类public class Article {private Integer id;//private int classid;//private int userid;private String title;private String content;private ArticleClass articleClass;private User user;public Article() {}/*public int getClassid() {return classid;}public void setClassid(int classid) {this.classid = classid;}public int getUserid() {return userid;}public void setUserid(int userid) {this.userid = userid;}*/public Article(String title, String content) {this.title = title;this.content = content;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}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;}public ArticleClass getArticleClass() {return articleClass;}public void setArticleClass(ArticleClass articleClass) {this.articleClass = articleClass;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}}

4、解决方案
问题主要发生在查找文章的时候，如果把文章类型信息和用户信息也查出来并存储在article对象的user和articleClass中
article映射文件如下
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://java.plugbase.org/dtd/sql-map-2.dtd">

<sqlMap namespace="article">
<typeAlias alias="Article" type="ebiz.sql.article.Article"/>
<typeAlias alias="ArticleClass" type="ebiz.sql.article.ArticleClass"/>
<typeAlias alias="User" type="ebiz.sql.user.User"/>

<resultMap id="articleResult">
<result property="id" column="aid"/>
<result property="title" column="title"/>
<result property="content" column="content"/>
<result property="articleClass" select="getArticleClassById" column="classid"/>
<result property="user" select="getUserById" column="userid"/>
</resultMap>


<select id="getArticleAllCascade" resultMap="articleResult">
select aid,title,content,classid, userid from article
</select>

<select id="getArticleByIdCascade" parameterresultMap="articleResult">
select aid,title,content,classid,userid from article
where article.aid = #id#
</select>


<insert id="insertArticle" parameterparameterparameterencoding="UTF-8" ?>

<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://java.plugbase.org/dtd/sql-map-2.dtd">
<sqlMap namespace="users">
<typeAlias alias="User" type="ebiz.sql.user.User"/>

<resultMap id="userResult">
<result property="id" column="id"/>
<result property="username" column="username"/>
<result property="password" column="password"/>
<result property="birth" column="birth"/>
<result property="gender" column="gender"/>
<result property="userType" column="user_type"/>
</resultMap>


<select id="getUsersAll" resultMap="userResult">
select id, username, password,birth,gender,user_type
from users
order by id desc
</select>

<select id="getUserById" parameterresultMap="userResult">
select id, username, password,birth,gender,user_type
from users
where id=#id#
</select>

<select id="getUserByNameAndPassword" parameterparameterresultMap="userResult">
select id, username, password,birth,gender,user_type
from users
where username=#username#
</select>


<insert id="insertUser" parameterparameterparameterencoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://java.plugbase.org/dtd/sql-map-2.dtd">

<sqlMap namespace="article_class">
<typeAlias alias="ArticleClass" type="ebiz.sql.article.ArticleClass"/>

<resultMap id="articleClassResult">
<result property="id" column="acid"/>
<result property="name" column="name"/>
<result property="desc" column="class_desc"/>
</resultMap>



<select id="getArticleClassById" parameterresultMap="articleClassResult">
select acid, name, class_desc from article_class where acid = #classid#
</select>
</sqlMap>

5、解释：当使用"getArticleByIdCascade"查询查询文章的时候，查出来之后分别把classid和userid作为参数调用"getUserById"和"getArticleClassById" 1 楼 phenom 2009-01-08 只有单向关联。 2 楼 walle1027 2009-03-05 会出现N+1查询的问题的。

ibatis多对一表联系关系映射的解决过程

热点推荐