Mybatis XML映射文件

mybatis为聚焦于sql而构建，sql映射文件常用的*元素如

• resultmap，是最复杂也是最强大的元素，用来描述如何从数据库结果集中来加载对象。 
• insert，映射插入语句
• update， 映射更新语句
• delete ， 映射删除语句
• select ， 映射查询语句

1）简单的单表映射文件

<?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.mybatis.bean.usermapper">
    <select id="getuser" parametertype="int"  resulttype="com.mybatis.bean.user">
        select * from users where id=#{id}
    </select>

    <insert id="insertuser" parametertype="com.mybatis.bean.user">
        insert into users(name,age) values(#{name},#{age});
    </insert>

    <update id="updateuser" parametertype="com.mybatis.bean.user">
       update  users set name=#{name} ,age=#{age} where id=#{id}
    </update>

    <delete id="deleteuser" parametertype="int">
        delete from users where id=#{id}
    </delete>

    <select id="alluser" resulttype="com.mybatis.bean.user">
        select * from users
    </select>
</mapper>

java对象

public class user {

    private int id;
    private string name;
    private int age;

    public int getid() {
        return id;
    }

    public string getname() {
        return name;
    }

    public int getage() {
        return age;
    }

    public void setid(int id) {
        this.id = id;
    }

    public void setname(string name) {
        this.name = name;
    }

    public void setage(int age) {
        this.age = age;
    }
 
}

 2）结果映射resultmap 元素是 mybatis 中最重要最强大的元素。当列名和属性名没有精确匹配，可以在select语句中对列使用别名，或配置显式的结果映射。

java对象

public class classes {
  
    private int id;
    private string name;
    private teacher teacher; 
    // 省略
}

resultmap映射文件、关联对象

<?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.mybatis.bean.classmapper">
    <select id="getclass" parametertype="int" resultmap="classresultmap">
       select * from class c,teacher t where c.teacher_id = t.t_id and c.c_id=#{id}
    </select>

    <resultmap id="classresultmap" type="classes">
     <id property="id" column="c_id"/>
     <result property="name" column="c_name"/>
     <association property="teacher" column="teacher_id" javatype="teacher">
           <id property="id" column="t_id"/>
           <result property="name" column="t_name"/>
     </association>
    </resultmap>
    
</mapper>

集合配置

<collection property="posts" oftype="domain.blog.post">
  <id property="id" column="post_id"/>
  <result property="subject" column="post_subject"/>
  <result property="body" column="post_body"/>
</collection>

　

参考文献：mybatis官网