这篇文章主要介绍mybatis映射XML文件的示例分析，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！

mybatis映射XML文件

一个简单的映射文件：

<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEmapperPUBLIC"-//mybatis.org//DTDMapper3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mappernamespace="com.cnx.wxcar.mapper.CustomerMapper"></mapper>

当然这个文件中没有任何的元素

The Mapper XML files have only a few first class elements :

cache – Configuration of the cache for a given namespace.

cache-ref – Reference to a cache configuration from another namespace.

resultMap – The most complicated and powerful element that describes how to load your objects from the database result sets.

sql – A reusable chunk of SQL that can be referenced by other statements.

insert – A mapped INSERT statement.

update – A mapped UPDATE statement.

delete – A mapped DELETE statement.

select – A mapped SELECT statement.

select

简单的例子：

<selectid="selectPerson"parameterType="int"resultType="hashmap">SELECT*FROMPERSONWHEREID=#{id}</select>

select也有很多属性可以让你配置：

<selectid="selectPerson"parameterType="int"parameterMap="deprecated"resultType="hashmap"resultMap="personResultMap"flushCache="false"useCache="true"timeout="10000"fetchSize="256"statementType="PREPARED"resultSetType="FORWARD_ONLY">

insert, update and delete

<insertid="insertAuthor"parameterType="domain.blog.Author"flushCache="true"statementType="PREPARED"keyProperty=""keyColumn=""useGeneratedKeys=""timeout="20"><updateid="updateAuthor"parameterType="domain.blog.Author"flushCache="true"statementType="PREPARED"timeout="20"><deleteid="deleteAuthor"parameterType="domain.blog.Author"flushCache="true"statementType="PREPARED"timeout="20">

语句：

<insertid="insertAuthor">insertintoAuthor(id,username,password,email,bio)values(#{id},#{username},#{password},#{email},#{bio})</insert><updateid="updateAuthor">updateAuthorsetusername=#{username},password=#{password},email=#{email},bio=#{bio}whereid=#{id}</update><deleteid="deleteAuthor">deletefromAuthorwhereid=#{id}</delete>

f your database supports auto-generated key fields (e.g. MySQL and SQL Server)，上面的插入语句可以写成：

<insertid="insertAuthor"useGeneratedKeys="true"keyProperty="id">insertintoAuthor(username,password,email,bio)values(#{username},#{password},#{email},#{bio})</insert>

如果你的数据库还支持多条记录插入，可以使用下面这个语句：

<insertid="insertAuthor"useGeneratedKeys="true"keyProperty="id">insertintoAuthor(username,password,email,bio)values<foreachitem="item"collection="list"separator=",">(#{item.username},#{item.password},#{item.email},#{item.bio})</foreach></insert>

sql

这个element可以定义一些sql代码的碎片，然后在多个语句中使用，降低耦合。比如：

<sqlid="userColumns">${alias}.id,${alias}.username,${alias}.password</sql>

然后在下面的语句中使用：

<selectid="selectUsers"resultType="map">select<includerefid="userColumns"><propertyname="alias"value="t1"/></include>,<includerefid="userColumns"><propertyname="alias"value="t2"/></include>fromsome_tablet1crossjoinsome_tablet2</select>

Result Maps

官网给了个最最复杂的例子

大体意思呢就是一个博客系统有一个作者，很多博文，博文中有一个作者，很多评论，很多标签（包括了一对多，一对一）

<!--VeryComplexStatement--><selectid="selectBlogDetails"resultMap="detailedBlogResultMap">selectB.idasblog_id,B.titleasblog_title,B.author_idasblog_author_id,A.idasauthor_id,A.usernameasauthor_username,A.passwordasauthor_password,A.emailasauthor_email,A.bioasauthor_bio,A.favourite_sectionasauthor_favourite_section,P.idaspost_id,P.blog_idaspost_blog_id,P.author_idaspost_author_id,P.created_onaspost_created_on,P.sectionaspost_section,P.subjectaspost_subject,P.draftasdraft,P.bodyaspost_body,C.idascomment_id,C.post_idascomment_post_id,C.nameascomment_name,C.commentascomment_text,T.idastag_id,T.nameastag_namefromBlogBleftouterjoinAuthorAonB.author_id=A.idleftouterjoinPostPonB.id=P.blog_idleftouterjoinCommentConP.id=C.post_idleftouterjoinPost_TagPTonPT.post_id=P.idleftouterjoinTagTonPT.tag_id=T.idwhereB.id=#{id}</select><!--VeryComplexResultMap--><resultMapid="detailedBlogResultMap"type="Blog"><constructor><idArgcolumn="blog_id"javaType="int"/></constructor><resultproperty="title"column="blog_title"/><associationproperty="author"javaType="Author"><idproperty="id"column="author_id"/><resultproperty="username"column="author_username"/><resultproperty="password"column="author_password"/><resultproperty="email"column="author_email"/><resultproperty="bio"column="author_bio"/><resultproperty="favouriteSection"column="author_favourite_section"/></association><collectionproperty="posts"ofType="Post"><idproperty="id"column="post_id"/><resultproperty="subject"column="post_subject"/><associationproperty="author"javaType="Author"/><collectionproperty="comments"ofType="Comment"><idproperty="id"column="comment_id"/></collection><collectionproperty="tags"ofType="Tag"><idproperty="id"column="tag_id"/></collection><discriminatorjavaType="int"column="draft"><casevalue="1"resultType="DraftPost"/></discriminator></collection></resultMap>

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