mybatis映射XML文件
一个简单的映射文件：
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<?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：
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<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：
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<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
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<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：
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<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：
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<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：
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<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：
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<sql id="userColumns"> ${alias}.id,${alias}.username,${alias}.password </sql> |
然后在下面的语句中使用：
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<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）
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<!-- 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> |
感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！
原文链接：https://my.oschina.net/gef/blog/704880
