mybatis返回HashMap结果类型与映射

gdrocket · 发表于 2016-11-27 11:48:05

Xhtml代码

<select id="selectBlogRetHashMap" parameterType="int" resultType="map">
SELECT id AS "id", title AS "title", content AS "content" FROM Blog WHERE id = #{id}
</select>

测试代码：Java代码

/**
* 测试返回HashMap
*/
@SuppressWarnings("unchecked")
@Test
public void testSelectBlogRetHashMap() {
SqlSession session = sqlSessionFactory.openSession();
HashMap<String,Object> blog = (HashMap<String,Object>) session.selectOne(
"cn.enjoylife.BlogMapper.selectBlogRetHashMap", 15);
session.close();
System.out.println(blog.get("title"));
}

ibatis高级映射：

表结构:

Java代码

create table BLOG
(
ID NUMBER(20),
TITLE VARCHAR2(50),
CONTENT VARCHAR2(4000),
BLOG_AUTHOR_ID NUMBER(20)
)
create table AUTHOR
(
ID NUMBER(20),
AUTHOR_NAME VARCHAR2(50)
);
create table POSTS
(
ID NUMBER(20),
SUBJECT VARCHAR2(50),
BODY VARCHAR2(4000),
BLOG_ID NUMBER(20)
)

bean信息：Java代码

package cn.enjoylife.domain;
import java.util.List;
public class Blog {
private Integer id;
private String title;
private String content;
private Author author;
private List<Post> posts/*=new ArrayList<Post>()*/;
public List<Post> getPosts() {
return posts;
}
public void setPosts(List<Post> posts) {
this.posts = posts;
}
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 Author getAuthor() {
return author;
}
public void setAuthor(Author author) {
this.author = author;
}
@Override
public String toString() {
return "Blog [content=" + content + ", id=" + id + ", title=" + title
+ "]";
}
}

Java代码

package cn.enjoylife.domain;
public class Author {
private Integer id;
private String name;
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;
}
@Override
public String toString() {
// System.out.println("Author[id="+id+",name="+name+"]");
return "Author[id="+id+",name="+name+"]";
}
}

Java代码

package cn.enjoylife.domain;
public class Post {
private Integer id;
private String subject;
private String postContent;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getSubject() {
return subject;
}
public void setSubject(String subject) {
this.subject = subject;
}
public String getPostContent() {
return postContent;
}
public void setPostContent(String postContent) {
this.postContent = postContent;
}
@Override
public String toString() {
return "Post [postContent=" + postContent + ", id=" + id + ", subject=" + subject
+ "]";
}
}

Blog.xmll配置:Xhtml代码

<!--
一对一关联嵌套查询应用select属性
1)id="selectBlogAndRelatedAuthor" 中的 blog_author_id 对应到
<association property="author" column="blog_author_id"/>中的column="blog_author_id"
2)我们执行selectBlogAndRelatedAuthor 1次之后，所产生的每条记录都要再进行一个查询来获取author信息（N），
这就是N+1问题，应该使用延迟加载的方式，否则这有可能产生致命的后果。
3)对于一对一关联,我设置了
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
</settings>
却没有对Author进行延迟加载，不知为何。。。
-->
<resultMap id="blogResult" type="Blog" >
<association property="author" column="blog_author_id"
javaType="Author" select="selectAuthor" />
</resultMap>
<select id="selectBlogAndRelatedAuthor" parameterType="int" resultMap="blogResult" >
SELECT id,title,content,blog_author_id FROM blog WHERE id = #{id}
</select>
<select id="selectAuthor" parameterType="int" resultType="Author">
SELECT id,author_name as "name" FROM author WHERE id = #{id}
</select>
<!--
一对一关联嵌套结果
-->
<resultMap id="blogResult2" type="Blog">
<id property="id" column="id" />
<result property="title" column="title"/>
<association property="author" column="blog_author_id"
javaType="Author">
<id property="id" column="author_id"/>
<result property="name" column="author_name"/>
</association>
</resultMap>
<select id="selectBlogAndRelatedAuthor2" parameterType="int" resultMap="blogResult2" >
SELECT t.ID, t.TITLE, t.CONTENT, a.id as "author_id", a.author_name
FROM blog t
INNER JOIN author a ON t.BLOG_AUTHOR_ID = a.ID
AND t.ID = #{id}
</select>
<!--
一对多关联嵌套查询，应用select属性
<collection property="posts" column="id" javaType="ArrayList" ofType="Post"
select="selectPosts"/>中的column指得是Post所对应表中的引用的主表中的主键id,
注意：这个column指的是主表（Blog)中的id,我在这犯了个错，写为Post所对应表中的外键id,这是不对的，
应为所引用主表的主键id。
property="posts" javaType="ArrayList" ofType="Post" 指属性posts为元素为Post的ArrayList类型
同样没有进行延迟加载，不知为何。。。
-->
<resultMap type="Blog" id="blogResult3" >
<id property="id" column="id"/>
<result property="title" column="title"/>
<result property="content" column="content"/>
<collection property="posts" column="id" javaType="ArrayList" ofType="Post"
select="selectPosts"/>
</resultMap>
<select id="selectBlogAndRelatedPosts" parameterType="int" resultMap="blogResult3" >
SELECT id, title, content FROM blog WHERE id = #{id}
</select>
<select id="selectPosts" parameterType="int" resultType="Post" >
SELECT p.id,p.subject,p.body as "postContent" FROM posts p WHERE p.blog_id =#{id}
</select>
<!--
一对多关联嵌套结果,在使用这种方式时，sql语句应该使用别名以保证不重复，如果不这样，可能
出现结果不正确的现象，比如以下的post_id别名
-->
<resultMap type="Blog" id="blogResultVersion" >
<id property="id" column="id" />
<result property="title" column="title"/>
<result property="content" column="content"/>
<collection property="posts" javaType="ArrayList" ofType="Post" column="id">
<id property="id" column="post_id"/>
<result property="subject" column="subject"/>
<result property="postContent" column="postContent"/>
</collection>
</resultMap>
<select id="selectBlogAndRelatedPosts2" parameterType="int" resultMap="blogResultVersion">
SELECT t.id, t.title, t.content, p.id as "post_id", p.subject, p.BODY as "postContent"
FROM blog t
left outer JOIN posts p ON t.id = p.blog_id
WHERE t.ID = #{id}
</select>

测试代码：Java代码

/**
* 测试一对一关联嵌套查询
*/
@Test
public void testSelectBlogAndRelatedAuthor() {
SqlSession session = sqlSessionFactory.openSession();
Blog blog = (Blog) session.selectOne(
"cn.enjoylife.BlogMapper.selectBlogAndRelatedAuthor", 15);
System.out.println(blog.toString());
session.close();
System.out.println(blog.getAuthor());
}
/**
* 测试一对一关联嵌套结果
*/
@Test
public void testSelectBlogAndRelatedAuthor2() {
SqlSession session = sqlSessionFactory.openSession();
Blog blog = (Blog) session.selectOne(
"cn.enjoylife.BlogMapper.selectBlogAndRelatedAuthor2", 15);
session.close();
System.out.println(blog.toString());
System.out.println(blog.getAuthor());
}
/**
* 测试一对多关联嵌套查询
*/
@Test
public void testSelectBlogAndRelatedPosts() throws Exception {
SqlSession session = sqlSessionFactory.openSession();
Blog blog = (Blog) session.selectOne(
"cn.enjoylife.BlogMapper.selectBlogAndRelatedPosts", 15);
System.out.println(blog.toString());
session.close();
System.out.println(blog.getPosts());
}
/**
* 测试一对多关联嵌套结果
*/
@Test
public void testSelectBlogAndRelatedPosts2() throws Exception {
SqlSession session = sqlSessionFactory.openSession();
Blog blog = (Blog) session.selectOne(
"cn.enjoylife.BlogMapper.selectBlogAndRelatedPosts2", 15);
session.close();
System.out.println(blog.toString());
System.out.println(blog.getPosts());
}

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