mybatis映射XML文件详解及实例
投稿：lqh
这篇文章主要介绍了mybatis映射XML文件详解及实例的相关资料,需要的朋友可以参考下
mybatis映射XML文件
一个简单的映射文件：
<?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="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：
<select id="selectPerson" parameterType="int" resultType="hashmap">
SELECT * FROM PERSON WHERE ID = #{id}
</select>
select也有很多属性可以让你配置：
<select id="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
<insert id="insertAuthor" parameterType="domain.blog.Author" flushCache="true" statementType="PREPARED" keyProperty="" keyColumn="" useGeneratedKeys="" timeout="20"> <update id="updateAuthor" parameterType="domain.blog.Author" flushCache="true" statementType="PREPARED" timeout="20"> <delete id="deleteAuthor" parameterType="domain.blog.Author" flushCache="true" statementType="PREPARED" timeout="20">
语句：
<insert id="insertAuthor">
insert into Author (id,username,password,email,bio)
values (#{id},#{username},#{password},#{email},#{bio})
</insert>
<update id="updateAuthor">
update Author set
username = #{username},
password = #{password},
email = #{email},
bio = #{bio}
where id = #{id}
</update>
<delete id="deleteAuthor">
delete from Author where id = #{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：
<insert id="insertAuthor" useGeneratedKeys="true"
keyProperty="id">
insert into Author (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：
<insert id="insertAuthor" useGeneratedKeys="true"
keyProperty="id">
insert into Author (username, password, email, bio) values
<foreach item="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：
<sql id="userColumns"> ${alias}.id,${alias}.username,${alias}.password </sql>
然后在下面的语句中使用：
<select id="selectUsers" resultType="map"> select <include refid="userColumns"><property name="alias" value="t1"/></include>, <include refid="userColumns"><property name="alias" value="t2"/></include> from some_table t1 cross join some_table t2 </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）
<!-- Very Complex Statement -->
<select id="selectBlogDetails" resultMap="detailedBlogResultMap">
select
B.id as blog_id,
B.title as blog_title,
B.author_id as blog_author_id,
A.id as author_id,
A.username as author_username,
A.password as author_password,
A.email as author_email,
A.bio as author_bio,
A.favourite_section as author_favourite_section,
P.id as post_id,
P.blog_id as post_blog_id,
P.author_id as post_author_id,
P.created_on as post_created_on,
P.section as post_section,
P.subject as post_subject,
P.draft as draft,
P.body as post_body,
C.id as comment_id,
C.post_id as comment_post_id,
C.name as comment_name,
C.comment as comment_text,
T.id as tag_id,
T.name as tag_name
from Blog B
left outer join Author A on B.author_id = A.id
left outer join Post P on B.id = P.blog_id
left outer join Comment C on P.id = C.post_id
left outer join Post_Tag PT on PT.post_id = P.id
left outer join Tag T on PT.tag_id = T.id
where B.id = #{id}
</select>
<!-- Very Complex Result Map -->
<resultMap id="detailedBlogResultMap" type="Blog">
<constructor>
<idArg column="blog_id" javaType="int"/>
</constructor>
<result property="title" column="blog_title"/>
<association property="author" javaType="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"/>
<result property="favouriteSection" column="author_favourite_section"/>
</association>
<collection property="posts" ofType="Post">
<id property="id" column="post_id"/>
<result property="subject" column="post_subject"/>
<association property="author" javaType="Author"/>
<collection property="comments" ofType="Comment">
<id property="id" column="comment_id"/>
</collection>
<collection property="tags" ofType="Tag" >
<id property="id" column="tag_id"/>
</collection>
<discriminator javaType="int" column="draft">
<case value="1" resultType="DraftPost"/>
</discriminator>
</collection>
</resultMap>
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