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Category与Article双向一对多关联
(1)将CategoryDao进行实现
public class CategoryDaoImpl extends BaseDao<Category> implements CategoryDao {
@Override
public boolean addCategory(Category category) {
try {
super.add(category);
return true;
} catch (Exception e) {
e.printStackTrace();
return false;
}
}
@Override
public Category getCategoryById(int id) {
return super.getById(id);
}
@Override
public List<Category> getAllCategorys() {
return super.getAll();
}
}
(2)将ArticleDao进行实现
public class ArticleDaoImpl extends BaseDao<Article> implements ArticleDao {
@Override
public boolean addArticle(Article article) {
try {
super.add(article);
return true;
} catch (Exception e) {
e.printStackTrace();
return false;
}
}
@Override
public Article getArticleById(int id) {
return super.getById(id);
}
@Override
public List<Article> getAllArticles() {
return super.getAll();
}
@Override
public List<Article> getArticelsByCategory(int categoryId) {
Map<String,Object> params = new HashMap<String,Object>();
params.put("cid", categoryId);
return super.getList("SelectByCategory", params);
}
@Override
public List<Article> getArticlesByTitle(String title) {
Map<String,Object> params = new HashMap<String,Object>();
params.put("title", title);
return super.getList("SelectByTitle", params);
}
}
》》》》》》》》》》》》》》》》》》》》》
由于Article对User和Category做了多对一关联，所以添加数据时外键添加会有问题
所以，在制作映射文件前，要对Article实体类进行修改，将表中外键列的对应属性加入到实体类中
//多对一的引用
private Category category;
private int cateId;
//多对一的引用
private User user;
private int userId;
-------注意上面对实体类的修改，增加两个基于外键的属性设置（userId,cateId）
public void setCategory(Category category) {
this.setCateId(category.getId());
this.category = category;
}
public void setUser(User user) {
this.setUserId(user.getId());
this.user = user;
}
--------------注意上面代码的修改，将两个原有属性set方法加入的红色代码
======================================
（3）Category映射文件
<?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="cn.smartapp.blogs.pojo.Category">
<resultMap type="Category" id="CategoryResult">
<id column="cid" property="id" />
<result column="cate_name" property="cateName" />
<!-- 一对多关联的设置 -->
<collection property="articels" ofType="Article" javaType="java.util.Set">
<id column="aid" property="id"/>
<result column="art_title" property="title"/>
<result column="art_content" property="content"/>
<result column="art_pubtime" property="pubTime" javaType="java.util.Date"/>
</collection>
</resultMap>
<insert id="insertPojo" parameterType="Category" useGeneratedKeys="true">
insert into blog_category(cate_name) values(#{cateName})
</insert>
<select id="SelectById" resultMap="CategoryResult" parameterType="int">
select
tc.id as cid,
tc.cate_name,
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id
from blog_category as tc inner join blog_article as ta
on tc.id=ta.cate_id
where tc.id=#{id}
</select>
<select id="SelectAll" resultMap="CategoryResult">
select
tc.id as cid,
tc.cate_name,
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id
from blog_category as tc inner join blog_article as ta
on tc.id=ta.cate_id
</select>
</mapper>
（4）Article映射文件
<?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="cn.smartapp.blogs.pojo.Article">
<resultMap type="Article" id="ArticleResult">
<id column="aid" property="id" />
<result column="art_title" property="title" />
<result column="art_content" property="content" />
<result column="art_pubtime" property="pubTime" javaType="java.util.Date"/>
<!-- 多对一的设置(Article与User) -->
<association property="User" foreignColumn="pub_user_id">
<id column="uid" property="id" />
<result column="user_name" property="userName" />
<result column="user_pass" property="password" />
<result column="nick_name" property="nickName" />
</association>
<!-- 多对一的设置（Article与Category） -->
<association property="Category" foreignColumn="cate_id">
<id column="cid" property="id" />
<result column="cate_name" property="cateName" />
</association>
</resultMap>
<insert id="insertPojo" parameterType="Article" useGeneratedKeys="true">
insert into blog_article(art_title,art_content,art_pubtime,pub_user_id,cate_id)
values(#{title},#{content},#{pubTime},#{userId},#{cateId})
<selectKey >
</selectKey>
</insert>
<select id="SelectById" resultMap="ArticleResult" parameterType="int">
select
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id,
tu.id as uid,
tu.user_name,
tu.user_pass,
tu.nick_name,
tc.id as cid,
tc.cate_name
from blog_user as tu inner join blog_article as ta on tu.id=ta.pub_user_id
inner join blog_category as tc on tc.id=ta.cate_id where ta.id=#{id}
</select>
<select id="SelectAll" resultMap="ArticleResult">
select
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id,
tu.id as uid,
tu.user_name,
tu.user_pass,
tu.nick_name,
tc.id as cid,
tc.cate_name
from blog_user as tu inner join blog_article as ta on tu.id=ta.pub_user_id
inner join blog_category as tc on tc.id=ta.cate_id
</select>
<select id="SelectByCategory" resultMap="ArticleResult">
select
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id,
tu.id as uid,
tu.user_name,
tu.user_pass,
tu.nick_name,
tc.id as cid,
tc.cate_name
from blog_user as tu inner join blog_article as ta on tu.id=ta.pub_user_id
inner join blog_category as tc on tc.id=ta.cate_id where tc.id=#{cid}
</select>
<select id="SelectByTitle" resultMap="ArticleResult">
select
ta.id as aid,
ta.art_title,
ta.art_content,
ta.art_pubtime,
ta.pub_user_id,
ta.cate_id,
tu.id as uid,
tu.user_name,
tu.user_pass,
tu.nick_name,
tc.id as cid,
tc.cate_name
from blog_user as tu inner join blog_article as ta on tu.id=ta.pub_user_id
inner join blog_category as tc on tc.id=ta.cate_id where ta.title like #{title}
</select>
</mapper>
=========================
(5)测试Article级联添加操作
public class ArticleDaoAddTest {
@Test
public void test() {
ArticleDao articleDao = new ArticleDaoImpl();
CategoryDao categoryDao = new CategoryDaoImpl();
Article article = new Article(); //新建一个即将被添加的Article对象
article.setTitle("今天是个写Java代码的好日子！"); //指定标题
Calendar calendar = Calendar.getInstance(); //创建日期对象
article.setPubTime(calendar.getTime()); //设置发布时间为当前时间
Category category = categoryDao.getCategoryById(1); //查询指定分类
article.setCategory(category); //将指定的分类设置到Article对象（为文章指定分类）
User user = new User(); //创建一个用户
user.setId(4); //指定用户为数据库表中id为4的用户
article.setUser(user); //为文章指定发布用户
article.setContent("哈哈哈哈哈哈。。。。"); //设置文章的内容
boolean doFlag = articleDao.addArticle(article); //添加文章
Assert.assertTrue(doFlag);
}
（6）测试Category与Article一对多关联是否好用
public class CategoryDaoSelectTest {
@Test
public void test() {
CategoryDao categoryDao = new CategoryDaoImpl();
Category category = categoryDao.getCategoryById(1);
int articleCount = category.getArticels().size();
//由于做了关联关系，所以一个分类(Category)中包含多个文章(Article)
for (Article article: category.getArticels()) {
System.out.println(article.getTitle());
}
Assert.assertEquals(articleCount, 5);
}
}
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原文地址：http://www.cnblogs.com/MrzhangKk/p/5164661.html
