三張表：user article blog
表的存儲sql文件：
/*
Navicat MySQL Data Transfer
Source Server : localhost
Source Server Version : 50620
Source Host : localhost:3306
Source Database : mybatis
Target Server Type : MYSQL
Target Server Version : 50620
File Encoding : 65001
Date: 2014-10-19 18:27:31
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for `user`
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`userName` varchar(50) DEFAULT NULL,
`userAge` int(11) DEFAULT NULL,
`userAddress` varchar(200) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'summer', '30', 'shanghai');
INSERT INTO `user` VALUES ('2', 'test1', '22', 'suzhou');
INSERT INTO `user` VALUES ('3', 'test1', '29', 'some place');
INSERT INTO `user` VALUES ('4', 'lu', '28', 'some place');
INSERT INTO `user` VALUES ('5', 'xiaoxun', '27', 'nanjing');
-- ----------------------------
-- Table structure for `article`
-- ----------------------------
DROP TABLE IF EXISTS `article`;
CREATE TABLE `article` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`userid` int(11) NOT NULL,
`title` varchar(100) DEFAULT NULL,
`content` text,
`blogid` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of article
-- ----------------------------
INSERT INTO `article` VALUES ('1', '1', 'test_title_1', 'test_content_1', '1');
INSERT INTO `article` VALUES ('2', '1', 'test_title_2', 'test_content_2', '1');
INSERT INTO `article` VALUES ('3', '1', 'test_title_3', 'test_content_3', '2');
INSERT INTO `article` VALUES ('4', '1', 'test_title_4', 'test_content_4', '2');
INSERT INTO `article` VALUES ('5', '2', 'test_title_5', 'test_content_5', '2');
-- ----------------------------
-- Table structure for `blog`
-- ----------------------------
DROP TABLE IF EXISTS `blog`;
CREATE TABLE `blog` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(200) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of blog
-- ----------------------------
INSERT INTO `blog` VALUES ('1', 'xiaoxun_blog');
INSERT INTO `blog` VALUES ('2', 'zhang_blog');
配置文件Configuration.xml
複製代碼
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- mybatis別名定義 -->
<typeAliases>
<typeAlias alias="User" type="com.mybatis.test.User"/>
<typeAlias alias="Article" type="com.mybatis.test.Article"/>
<typeAlias alias="Blog" type="com.mybatis.test.Blog"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis" />
<property name="username" value="root"/>
<property name="password" value="admin"/>
</dataSource>
</environment>
</environments>
<!-- mybatis的mapper文件，每個xml配置文件對應一個接口 -->
<mappers>
<mapper resource="com/mybatis/test/User.xml"/>
<mapper resource="com/mybatis/test/Article.xml"/>
<mapper resource="com/mybatis/test/Blog.xml"/>
</mappers>
</configuration>
User類的定義和User.xml的配置見上一文章。
Article類定義：
package com.mybatis.test;
public class Article {
private int id;
private User user;
private String title;
private String content;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
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;
}
}
Article類中有一個User類。
Article.xml的配置：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.test.IArticleOperation">
<resultMap type="User" id="userResultMap">
<!-- 屬性名和數據庫列名映射 -->
<id property="id" column="user_id" />
<result property="userName" column="user_userName" />
<result property="userAge" column="user_userAge" />
<result property="userAddress" column="user_userAddress" />
</resultMap>
<!-- User join Article進行聯合查詢 (一對一)-->
<resultMap id="articleResultMap" type="Article">
<id property="id" column="article_id" />
<result property="title" column="article_title" />
<result property="content" column="article_content" />
<!-- 將article的user屬性映射到userResultMap -->
<association property="user" javaType="User" resultMap="userResultMap"/>
</resultMap>
<!-- 使用別名來映射匹配 -->
<select id="getUserArticles" parameterType="int" resultMap="articleResultMap">
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>
<!-- 另一種聯合查詢 (一對一)的實現，但是這種方式有“N+1”的問題 -->
<!-- <resultMap id="articleResultMap" type="Article">
<id property="id" column="article_id" />
<result property="title" column="article_title" />
<result property="content" column="article_content" />
<association property="user" javaType="User" column="userid" select="selectUser"/>
</resultMap>
<select id="selectUser" parameterType="int" resultType="User">
select * from user where id = #{id}
</select> -->
</mapper>
Blog類定義：
package com.mybatis.test;
import java.util.List;
public class Blog {
private int id;
private String title;
private List<Article> articles;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public List<Article> getArticles() {
return articles;
}
public void setArticles(List<Article> articles) {
this.articles = articles;
}
}
Blog類中有一個List<Article>。
Blog.xml配置：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.test.IBlogOperation">
<resultMap id="userResultMap" type="User">
<id property="id" column="user_id" />
<result property="userName" column="user_userName" />
<result property="userAge" column="user_userAge" />
<result property="userAddress" column="user_userAddress" />
</resultMap>
<resultMap id="articleResultMap" type="Article">
<id property="id" column="article_id" />
<result property="title" column="article_title" />
<result property="content" column="article_content" />
<association property="user" javaType="User" resultMap="userResultMap"/>
</resultMap>
<resultMap id="blogResultMap" type="Blog">
<id property="id" column="blog_id" />
<result property="title" column="blog_title" />
<!-- 將article list屬性映射到collection -->
<collection property="articles" ofType="Article" resultMap="articleResultMap"/>
</resultMap>
<!-- select語句 -->
<select id="getBlogByID" parameterType="int" resultMap="blogResultMap">
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}
</select>
</mapper>
IArticleOperation定義：
package com.mybatis.test;
import java.util.List;
public interface IArticleOperation {
public List<Article> getUserArticles(int userID);
}
IBlogOperation定義：
package com.mybatis.test;
public interface IBlogOperation {
Blog getBlogByID(int id);
}
Test類：
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 {
//通過配置文件初始化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<User> users = userOperation.selectUsersByName(userName);
for (User user : users) {
System.out.println(user.getId() + ":" + user.getUserName()
+ ":" + user.getUserAddress());
}
} finally {
session.close();
}
}
/**
* 增加後要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);
session.commit();
System.out.println("新增用戶ID：" + user.getId());
} finally {
session.close();
}
}
/**
* 修改後要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);
session.commit();
}
} finally {
session.close();
}
}
/**
* 刪除後要commit.
*
* @param id
*/
public void deleteUser(int id) {
SqlSession session = sqlSessionFactory.openSession();
try {
IUserOperation userOperation = session
.getMapper(IUserOperation.class);
userOperation.deleteUser(id);
session.commit();
} finally {
session.close();
}
}
public void getUserArticles(int userid) {
SqlSession session = sqlSessionFactory.openSession();
try {
IArticleOperation articleOperation = session
.getMapper(IArticleOperation.class);
List<Article> articles = articleOperation.getUserArticles(userid);
for (Article article : articles) {
System.out.println(article.getTitle() + ":"
+ article.getContent() + "用戶名："
+ article.getUser().getUserName() + "用戶地址："
+ 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<Article> articles = blog.getArticles();
for (Article article : articles) {
System.out.println(article.getTitle() + ":"
+ article.getContent() + "用戶名："
+ article.getUser().getUserName() + "用戶地址："
+ 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查詢問題”
<resultMap id=”blogResult” type=”Blog”>
<association property="author" column="blog_author_id"
javaType="Author" select=”selectAuthor” />
</resultMap>
<select id=”selectBlog” parameterType=”int” resultMap=”blogResult”>
SELECT * FROM BLOG WHERE ID = #{id}
</select>
<select id=”selectAuthor” parameterType=”int” resultType="Author">
SELECT * FROM AUTHOR WHERE ID = #{id}
</select>
有兩個查詢語句：一個來加載博客，另外一個來加載作者，而且博客的結果映射描述了“selectAuthor”語句應該被用來加載它的 author 屬性。
其他所有的屬性將會被自動加載，假設它們的列和屬性名相匹配。
這種方式很簡單，但是對於大型數據集合和列表將不會表現很好。問題就是我們熟知的“N+1 查詢問題”。概括地講，N+1 查詢問題可以是這樣引起的：
你執行了一個單獨的 SQL 語句來獲取結果列表（就是“+1”）。
對返回的每條記錄，你執行了一個查詢語句來爲每個加載細節（就是“N”）。
這個問題會導致成百上千的 SQL 語句被執行。這通常不是期望的。
可以採用關聯的嵌套結果來解決這個問題：
<resultMap id="blogResult" type="Blog">
<id property=”id” column="blog_id" />
<result property="title" column="blog_title" />
<association property="author" column="blog_author_id"
javaType="Author" resultMap=”authorResult” />
</resultMap>
<resultMap id="authorResult" type="Author">
<id property="id" column="author_id" />
<result property="username" column="author_username" />
<result property="password" column="author_password" />
<result property="email" column="author_email" />
<result property="bio" column="author_bio" />
</resultMap>
resultMap 這是結果映射的 ID，可以映射關聯的嵌套結果到一個合適的對象圖中。這是一種替代方法來調用另外一個查詢語句。
代碼下載：http://download.csdn.net/detail/luxiaoxun/8056559
參考：
http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html