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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