举例：
一个文章有一个用户，当查询文章时，显示文章信息和文章作者信息，这里不考虑一个文章多个作者的问题。
表结构：
文章表：
DROP TABLE IF EXISTS `article`; CREATE TABLE `article` ( `id` int(11) NOT NULL AUTO_INCREMENT, `article_name` varchar(50) NOT NULL COMMENT ‘文章名‘, `article_content` varchar(1000) NOT NULL COMMENT ‘文章内容‘, `author_id` int(11) NOT NULL COMMENT ‘作者id‘, `create_time` datetime NOT NULL COMMENT ‘创建时间‘, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
作者表：
DROP TABLE IF EXISTS `author`; CREATE TABLE `author` ( `id` int(11) NOT NULL AUTO_INCREMENT, `author_name` varchar(50) NOT NULL COMMENT ‘作者名‘, `author_age` int(11) NOT NULL COMMENT ‘作者年龄‘, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
文章实体:
package com.heli.core.user.model;
import java.io.Serializable;
import java.util.Date;
public class Article implements Serializable {
private Integer id;
private String articleName;
private String articleContent;
private Integer authorId;
private Date createTime;
private Author author;
public Author getAuthor() {
return author;
}
public void setAuthor(Author author) {
this.author = author;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getArticleName() {
return articleName;
}
public void setArticleName(String articleName) {
this.articleName = articleName;
}
public String getArticleContent() {
return articleContent;
}
public void setArticleContent(String articleContent) {
this.articleContent = articleContent;
}
public Integer getAuthorId() {
return authorId;
}
public void setAuthorId(Integer authorId) {
this.authorId = authorId;
}
public Date getCreateTime() {
return createTime;
}
public void setCreateTime(Date createTime) {
this.createTime = createTime;
}
}
作者实体：
package com.heli.core.user.model;
import java.io.Serializable;
public class Author implements Serializable {
private Integer id;
private String authorName;
private Integer authorAge;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getAuthorName() {
return authorName;
}
public void setAuthorName(String authorName) {
this.authorName = authorName;
}
public Integer getAuthorAge() {
return authorAge;
}
public void setAuthorAge(Integer authorAge) {
this.authorAge = authorAge;
}
}
文章的映射文件ArticleMapper.xml：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "mybatis-3-mapper.dtd" >
<mapper namespace="com.heli.core.user.mapper.ArticleMapper" >
<resultMap id="BaseResultMap" type="com.heli.core.user.model.Article" >
<id column="id" property="id" jdbcType="INTEGER" />
<result column="article_name" property="articleName" jdbcType="VARCHAR" />
<result column="article_content" property="articleContent" jdbcType="VARCHAR" />
<result column="author_id" property="authorId" jdbcType="INTEGER" />
<result column="create_time" property="createTime" jdbcType="TIMESTAMP" />
<association property="author" column="author_id" javaType="com.heli.core.user.model.Author" select="getAuthor" >
</resultMap>
<resultMap id="authorResultMap" type="com.heli.core.user.model.Author" >
<id column="id" property="id" jdbcType="INTEGER" />
<result column="author_name" property="authorName" jdbcType="VARCHAR" />
<result column="author_age" property="authorAge" jdbcType="INTEGER" />
</resultMap>
<sql id="Base_Column_List" >
id, article_name, article_content, author_id, create_time
</sql>
<select id="getAuthor" resultMap="authorResultMap" parameterType="java.lang.Integer" >
select
<include refid="Base_Column_List" />
from author
where id = #{authorId,jdbcType=INTEGER}
</select>
<select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
select
<include refid="Base_Column_List" />
from article
where id = #{id,jdbcType=INTEGER}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
delete from article
where id = #{id,jdbcType=INTEGER}
</delete>
<insert id="insert" parameterType="com.heli.core.user.model.Article" useGeneratedKeys="true" keyProperty="id" >
insert into article (article_name, article_content, author_id,
create_time)
values (#{articleName,jdbcType=VARCHAR}, #{articleContent,jdbcType=VARCHAR}, #{authorId,jdbcType=INTEGER},
#{createTime,jdbcType=TIMESTAMP})
</insert>
<insert id="insertSelective" parameterType="com.heli.core.user.model.Article" useGeneratedKeys="true" keyProperty="id" >
insert into article
<trim prefix="(" suffix=")" suffixOverrides="," >
article_name,
article_content,
author_id,
create_time,
</trim>
<trim prefix="values (" suffix=")" suffixOverrides="," >
#{articleName,jdbcType=VARCHAR},
#{articleContent,jdbcType=VARCHAR},
#{authorId,jdbcType=INTEGER},
#{createTime,jdbcType=TIMESTAMP},
</trim>
</insert>
<update id="updateByPrimaryKeySelective" parameterType="com.heli.core.user.model.Article" >
update article
<set >
<if test="articleName != null" >
article_name = #{articleName,jdbcType=VARCHAR},
</if>
<if test="articleContent != null" >
article_content = #{articleContent,jdbcType=VARCHAR},
</if>
<if test="authorId != null" >
author_id = #{authorId,jdbcType=INTEGER},
</if>
<if test="createTime != null" >
create_time = #{createTime,jdbcType=TIMESTAMP},
</if>
</set>
where id = #{id,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="com.heli.core.user.model.Article" >
update article
set article_name = #{articleName,jdbcType=VARCHAR},
article_content = #{articleContent,jdbcType=VARCHAR},
author_id = #{authorId,jdbcType=INTEGER},
create_time = #{createTime,jdbcType=TIMESTAMP}
where id = #{id,jdbcType=INTEGER}
</update>
</mapper>
这样查询文章时，就可以获取文章的作者信息了。
原文：http://my.oschina.net/ydsakyclguozi/blog/510533