mybatis使用xml进行增删改查代码解析

mybatis是支持普通sql查询、存储过程和高级映射的持久层框架。

mybatis消除了几乎所有的jdbc代码和参数的手工设置以及对结果集的检索封装。

mybatis可以使用 简单的xml或注解用于配置和原始映射，将接口和java的pojo(plain old java objects 普通的java对象)映射成数据库中的记录。

每一个mybatis应用程序都以一个sqlsessionfactory对象的实例为核心。

sqlsessionfactory对象的实例可以通过sqlsessionfactorybuilder对象来获得。sqlsessionfactorybuilder对象可以通过xml配置文件，或从以往使用管理中准备好的configuration类实例中来构建sqlsessionfactory对象。

【示例：使用配置类获取sqlsessionfactory】

datasource datasource = blogdatasourcefactory.getblogdatasource();
transactionfactory transactionfactory = new jdbctransactionfactory();
//环境
environment environment = new environment("development", transactionfactory, datasource);
configuration configuration = new configuration(environment);
//映射器类
configuration.addmapper(blogmapper.class);
sqlsessionfactory sqlsessionfactory = new sqlsessionfactorybuilder().build(configuration);

注意这种情况下配置是添加映射器类。映射器类是java类，这些类包含sql映射语句的注解从而避免了xml文件的依赖，但是xml映射仍然在 大多数高级映射(比如：嵌套join映射)时需要。

出于这样的原因，如果存在xml配置文件的话，mybatis将会自动查找和加载一个对等的xml文件(这种情况下，基于类路径下的blogmapper.class类的类名，那么blogmapper.xml将会被加载–即class 与 xml在同一个文件目录下。如果非，则需要手动配置加载xml)。

【1】基本增删改查xml配置

<?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.web.mapper.usermapper">

   <!-- 可以解决model属性名与数据表中column列名不一致问题 jdbctype一定要大写 -->  
   <resultmap type="user" id="usermap">
    <id property="id" column="id" javatype="int" jdbctype="integer"/>
    <result property="name" column="username" javatype="string" jdbctype="varchar"/>
    <result property="age" column="age" javatype="int" jdbctype="integer"/>
   </resultmap>

   <!--
   注意这里的result，如果column == property 则可以直接返回java object。
   如果属性名与列名不一致，解决方法如下：
   1. 使用resultmap; 
   2.返回hashmap ; 
   3.查询语句使用别名
   -->
   <select id="getuser" parametertype="int" resultmap="usermap">
    select * from t_user where id=#{id}
   </select>

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


   <update id="updateuser" parametertype="user" >
    update t_user set username=#{name},age=#{age} where id=#{id}
   </update>

   <insert id="insertuser" parametertype="user" >
    insert into t_user(username,age) values(#{name},#{age})
   </insert>

   <!-- model's attr(name) different from column(username), so the result use usermap -->

   <select id="getusers" resultmap="usermap">
    select * from t_user
   </select>
</mapper>

注册到mybatis.xml [当与spring结合时，将不需要这个配置文件]

mybatis的配置文件

<?xml version="1.0" encoding="utf-8"?>
<!doctype configuration public "-//mybatis.org//dtd config 3.0//en" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

  <properties resource="jdbc.properties"/>

  <!-- 配置实体类的别名 -->
  <typealiases>
    <!-- <typealias type="com.web.model.user" alias="user"/> -->
    <package name="com.web.model"/>
  </typealiases>
<!-- 
  development : 开发模式
  work : 工作模式
 -->
  <environments default="development">
    <environment id="development">
      <transactionmanager type="jdbc" />
      <datasource type="pooled">
        <property name="driver" value="${driver}" />
        <property name="url" value="${url}" />
        <property name="username" value="${username}" />
        <property name="password" value="${password}" />
      </datasource>
    </environment>
  </environments>

  <mappers>
    <mapper resource="com/web/mapper/usermapper.xml"/>
    <mapper resource="com/web/mapper/ordermapper.xml"/>
    <mapper class="com.web.mapperclass.usermapper"/>
  </mappers>
</configuration>

【2】通过sqlsessionfactory拿到session

这里使用xml文件获取sqlsessionfactory和sqlsession。

public static sqlsessionfactory getfactory(){
	/* flow the src dir*/
	string resource = "mybatis.xml";
	/*mybatisutils.class.getresourceasstream(resource)----- it's wrong !!!!
     * please distinguish the two up and down 
     * */
	inputstream inputstream = mybatisutils.class.getclassloader().getresourceasstream(resource);
	sqlsessionfactory factory = new sqlsessionfactorybuilder().build(inputstream);
	return factory;
}
sqlsession session = factory.opensession(true);
//默认手动提交；
/*
  两种解决方式：
  1.factory.opensession(true);
  2.session.commit();
  */

【3】增删改查后台测试代码

/*use sql xml not annotation*/
@test
  public void testadd(){
	sqlsession session = mybatisutils.getfactory().opensession();
	string statement = "com.web.mapper.usermapper.insertuser";
	/*return the effect rows*/
	int insert= session.insert(statement, new user("tom5", 15));
	/*default is not auto commit*/
	session.commit(true);
	session.close();
	system.out.println("effect rows.."+insert);
}
@test
  public void testselect(){
	/*set auto commit ,which equals to the above*/
	sqlsession session = mybatisutils.getfactory().opensession(true);
	string statement = "com.web.mapper.usermapper.getuser";
	/*return the effect rows*/
	user user = session.selectone(statement, 3);
	system.out.println("effect rows.."+user);
}
@test
  public void testupdate(){
	sqlsession session = mybatisutils.getfactory().opensession(true);
	string statement = "com.web.mapper.usermapper.updateuser";
	/*return the effect rows*/
	int update= session.update(statement, new user(3,"tom4", 13));
	system.out.println("effect rows.."+update);
}
@test
  public void testdelete(){
	sqlsession session = mybatisutils.getfactory().opensession();
	string statement = "com.web.mapper.usermapper.deleteuser";
	/*return the effect rows*/
	int delete= session.delete(statement, 6);
	/* commit by yourself*/
	session.commit();
	system.out.println("effect rows.."+delete);
	session.close();
}
@test
  public void testgetusers(){
	sqlsession session = mybatisutils.getfactory().opensession();
	string statement = "com.web.mapper.usermapper.getusers";
	/*return the list<user>*/
	list<user> users= session.selectlist(statement);
	session.commit();
	system.out.println("effect rows.."+users);
	session.close();
}

tips ：

parametertype 和 resulttype 为 hashmap ：

• mapper.xml :

<select id="getuserformap" parametertype="hashmap" resulttype="hashmap">
    select * from c_user where id=#{id};
  </select>

• test code :

@test
  public void getuserformap(){
	sqlsession session = mybatisutils.getfactory().opensession();
	string statement = "com.web.mapper.usermapper.getuserformap";
	hashmap<string, object> map = new hashmap<string, object>();
	map.put("id", 1);
	/*return the effect rows*/
	object selectone = session.selectone(statement, map);
	/*default is not auto commit*/
	session.commit(true);
	session.close();
	system.out.println("effect rows.."+selectone+" ,class :"+selectone.getclass());
}

• result as follows :

effect rows..{id=1, age=12, name=luli} ,class :class java.util.hashmap

综上可知：mybatis 会根据参数类型和结果类型，自动进行解析封装。

【扩展 基本方法】

【1】分页列表

 <select id="getlistpage" parametertype="hashmap" resultmap="siteextenddaomap">
    select id,site_id,site_name,site_number,province,city,area,address,internal_number,longitude,latitude
    from tb_site
    --使用动态sql
    <trim prefix="where" prefixoverrides="and |or "> 
      <if test="checkstate!= null and checkstate!=''">
        and check_state = #{checkstate,jdbctype=integer}
      </if>
      <if test="siteid!= null and siteid!=''">
        and site_id like concat('%',#{siteid},'%')
      </if>
      <if test="sitename!= null and sitename!=''">
        and site_name like concat('%',#{sitename},'%')
      </if>
      <if test="sitenumber!= null and sitenumber!=''">
        and site_number like concat('%', #{sitenumber},'%')
      </if>
      <if test="province!= null and province!=''">
        and province = #{province}
      </if>
      <if test="city!= null and city!=''">
        and city = #{city}
      </if>
      <if test="area!= null and area!=''">
        and area = #{area}
      </if>
    </trim> 
    --添加排序
    <if test="sortname!= null and sortname!='' and sortorder!= null and sortorder!=''">
      order by ${sortname} ${sortorder}
    </if>
    --添加分页
    limit ${(page-1)*pagesize},${pagesize}
 </select>

【2】删除方法–根据对象或者id

如果参数为pojo,mybatis会自动从对象里面获取id ;

  <delete id="delete" parametertype="user">
    delete from tb_user
    where
    id = #{id} 
  </delete>

  <delete id="deletebyid" parametertype="long">
    delete from tb_user
    where
    id = #{id} 
  </delete>

【3】根据 id list 删除数据

  <delete id="deletebyids">
    delete from tb_user
    where id in
    --使用foreach
    <foreach collection="list" item="id" open="(" separator=","close=")"> #{id} 
    </foreach>
  </delete>

【4】getrows

通常与getlistpage联合使用。

<select id="getrows" parametertype="hashmap" resulttype="long">
    select count(*) from tb_sys_role
    <if test="keysysrole!= null">
      <trim prefix="where" prefixoverrides="and |or ">
        <if test="keysysrole.id!= null">
        and id = #{keysysrole.id}
        </if>
        <if test="keysysrole.name!= null and keysysrole.name!=''">
        and name = #{keysysrole.name}
        </if>
        <if test="keysysrole.available!= null and keysysrole.available!=''">
        and available = #{keysysrole.available}
        </if>
      </trim>
    </if>
  </select>

总结

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