MyBatis技术总结模板

MyBatis技术总结模板

分类：JavaEE框架技术之Mybatis
作者：LL

• 什么是MyBatis？

  MyBatis 框架也被称之为 ORM（Object/Relational Mapping，即对象关系映射）框架。MyBatis是基于jdbc的持久化框架；它将数据库中的表与java中的实体类通过映射文件(xxxMapper.xml)与配置文件(config.xml)联系起来。支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。

• MyBatis中的主要组成部分

  MyBatis主要由配置文件(mybatisConfig.xml)、映射文件(xxxMapper.xml)、第三方jar包(核心jar包)、SqlSessionFactoryBuilder（类）、SqlSessionFactory（接口）、SqlSession（接口）、Resources（类）。

  SqlSession的实现类是DefaultSqlSession（可以通过控制台打印出来观察）
  SqlSessionFactory的实现类是：DefaultSqlSessionFactory

  SqlSessionFactory是用来创建SqlSession（会话的意思：连接+数据库操作+结果集+关闭)

  SqlSessionFactory 一旦被创建就应该在应用的运行期间一直存在，没有任何理由丢弃它或重新创建另一个实例。 使用 SqlSessionFactory 的最佳实践是在应用运行期间不要重复创建多次，多次重建 SqlSessionFactory 被视为一种代码“坏习惯”。因此 SqlSessionFactory 的最佳作用域是应用作用域。 有很多方法可以做到，最简单的就是使用单例模式或者静态单例模式。

  SqlSessionFactoryBuilder实例 随着SqlSessionFactory的创建而销毁，所以它的最佳作用域是方法作用域（也就是局部方法变量）。

  SqlSessionFactory创建代码示例：

  //1.读取配置文件
  InputStream in = Resources.getResourceAsStream("mybatis-config.xml");//注意配置文件放在类路径下(即src下面)；
  SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
  Sqlsession：每个线程都应该有它自己的 SqlSession 实例。SqlSession 的实例不是线程安全的，因此是不能被共享的，所以它的最佳的作用域是请求或方法作用域。
  SqlSession创建代码示例：
  SqlSession session=factory.openSession();
  

• MyBatis配置

  • 设置（settings）

  主要作用：开启日志文件与MyBatis框架运行规则配置

  设置（settings）代码示例：

  <setting name="logImpl" value="LOG4J"/>value指定具体使用的日志 ,name是指定的(不能变的),这里的value可以是"STDOUT_LOGGING"，若是log4j则需要写外部的properties文件
  

  • 类型别名（typeAliases）

  主要作用：类型别名是为 Java 类型设置一个短的名字。它只和 XML 配置有关，存在的意义仅在于用来减少类完全限定名的冗余。

  类型别名（typeAliases）代码示例：

  
  <typeAliases>
    <typeAlias type="com.apesource.entity.Employee" alias="Employee"/>
  typeAliases>
  
  <typeAliases>
  		
  		<package name="com.apesource.entity"/>
  typeAliases>
  

  • 环境配置（environments）

  主要作用：MyBatis 可以配置适应多种环境，这种机制有助于将 SQL 映射应用于多种数据库之中，如:测试环境，生产环境(实际的使用环境),一个environments下有多个environment

  环境配置（environments）代码示例：

  <environments default="development">
  	 
  	    <environment id="development">
  	    
  	      <transactionManager type="JDBC"/>
  	      
  	      <dataSource type="POOLED">
  	        <property name="driver" value="${jdbc_driver}"/>
  	        
  	        <property name="url" value="${jdbc_url}"/>
  	        <property name="username" value="${jdbc_user}"/>
  	        <property name="password" value="${jdbc_password}"/>
  	      dataSource>
  	    environment>
  environments>
  

  • 映射器（mappers）

  主要作用：将实体类与数据库中的表映射起来，每个实体类对应一个xxxMapper.xml映射文件（里面写SQL语句）；

  映射器（mappers）代码示例：

  
  
  <mapper namespace="com.apesource.dao.mapper.AnswerRecordMapper">
     <insert id="insertAnswerRecord" parameterType="AnswerRecord" useGeneratedKeys="true" keyProperty="recordId">
          insert into answer_record (respondent,question,right_answer,submit_answer,submit_datetime)
          values(#{respondent},#{question},#{rightAnswer},#{submitAnswer},now())
     insert>
     <delete id="deleteAnswerRecord" parameterType="int">
          delete from answer_record where 
          record_id=#{recordId}
     delete>
     
     <update id="updateAnswerRecord" parameterType="AnswerRecord">
         update answer_record 
      		              <set>
      		                 <if test="respondent!=null">respondent=#{respondent},if>
      		                 <if test="question!=null">question=#{question},if>
      		                 <if test="rightAnswer!=null">right_answer=#{rightAnswer},if>
      		                 <if test="submitAnswer!=null">submit_answer=#{submitAnswer},if>
      		                 submit_datetime=now()
     		              set>
                      where record_id=#{recordId}
      update>
      
  <select id="listAnswerRecordByRespondent" resultType="AnswerRecord">
      select record_id as recordId,
             respondent as respondent ,
             question    as question,
             right_answer  as rightAnswer,
             submit_answer  as submitAnswer,
              submit_datetime  as submitDatetime
      from   answer_record   
      where respondent=#{respondent}
  select>
     <select id="countAnswerRecordDataByRespondent" parameterType="AnswerRecord" resultType="map">
          SELECT COUNT(record_id) AS totalAnswer,
    (SELECT COUNT(record_id)  FROM answer_record 
    WHERE right_answer=submit_answer AND respondent='洪七公')
    AS rightAnswer,
    (SELECT COUNT(record_id)   FROM answer_record
     WHERE right_answer!=submit_answer AND respondent='洪七公')
    AS wrongAnswer
  FROM answer_record    
      WHERE respondent='洪七公'
     select>
     
     
      <insert id="insertBatchData" parameterType="list">
          INSERT INTO answer_record(respondent,question,right_answer,submit_answer,submit_datetime)VALUES
             <foreach collection="list" item="record" separator=",">
                   (
                     #{record.respondent},
                     #{record.question},
                     #{record.rightAnswer},
                     #{record.submitAnswer},
                    NOW()
                    
                   )
             foreach>
      insert>
      
      <delete id="deleteBatchData" parameterType="list">
      
        DELETE FROM answer_record WHERE
                       record_id  IN
                   <foreach collection="list" item="rid" open="(" close=")" separator=",">
                      #{rid}
                    foreach>
     delete>
     
      
      mapper>
      ```
  

• MyBatis XML 映射器

  1.常用节点作用总结

  • select :用于查询的SQL语句书写

  <select id="listAnswerRecordByRespondent" resultType="AnswerRecord">
            select record_id as recordId,
                   respondent as respondent ,
                   question    as question,
                   right_answer  as rightAnswer,
                   submit_answer  as submitAnswer,
                    submit_datetime  as submitDatetime
            from   answer_record   
            where respondent=#{respondent}
  select>
  

  • update:用于更新的SQL语句的书写

  <update id="updateAnswerRecord" parameterType="AnswerRecord">
           update answer_record 
  		  <set>
  		    <if test="respondent!=null">respondent=#{respondent},if>
  		    <if test="question!=null">question=#{question},if>
  		    <if test="rightAnswer!=null">right_answer=#{rightAnswer}if>
  		    <if test="submitAnswer!=null">submit_answer=#{submitAnswer}if>
  		  submit_datetime=now()
  		  set>
            where record_id=#{recordId}
  update>
  

  • delete：用于删除的SQL语句书写

  <delete id="deleteBatchData" parameterType="list">
       
         DELETE FROM answer_record WHERE
               record_id  IN
               <foreach collection="list" item="rid" open="(" close=")" separator=",">
                        #{rid}
               foreach>
  delete>
  

  • insert:用于插入数据的sql语句书写

  <insert id="insertAnswerRecord" parameterType="AnswerRecord" useGeneratedKeys="true" keyProperty="recordId">
           insert into answer_record (respondent,question,right_answer,submit_answer,submit_datetime)
           values(#{respondent},#{question},#{rightAnswer},#{submitAnswer},now())
  insert>
  

  2.常用属性作用总结

  • id 属性:里面写一个接口（xxxMapper.java）中的方法的名字
  • resultType 属性:是返回结果的类型
  • parameterType 属性：传入参数的类型
  • useGeneratedKeys属性:设置是否主键回填
  • keyProperty属性用于接收返回的主键的属性（一般是实体类的id属性）

  3.常见SQL映射示例

  示例1：普通增加

  SQL映射配置
  <insert id="insertAnswerRecord" parameterType="AnswerRecord" useGeneratedKeys="true" keyProperty="recordId">
  insert into answer_record (respondent,question,right_answer,submit_answer,submit_datetime)
  values(#{respondent},#{question},#{rightAnswer},#{submitAnswer},now())
  insert>
  

  接口方法定义
  int insertAnswerRecord(AnswerRecord answerRecord);
  

  示例2：批量增加

  <insert id="insertBatchData" parameterType="list">
  INSERT INTO answer_record(respondent,question,right_answer,submit_answer,submit_datetime)VALUES
  <foreach collection="list" item="record" separator=",">
  (
  #{record.respondent},
  #{record.question},
  #{record.rightAnswer},
  #{record.submitAnswer},
  NOW()
  
  )
  foreach>
  insert>SQL映射配置
  

  接口方法定义
  int insertBatchData(List<AnswerRecord>listBat);
  

  示例3：普通删除

  SQL映射配置
  <delete id="deleteAnswerRecord" parameterType="list">
  DELETE FROM answer_record WHERE record_id = #{recordId}
  foreach>
  delete>
  

  接口方法定义
  int deleteAnswerRecord(int recordId);
  

  示例4：批量删除

  <delete id="deleteBatchData" parameterType="list">
  DELETE FROM answer_record WHERErecord_id  IN
  <foreach collection="list" item="rid" open="(" close=")" separator=","> #{rid}
  foreach>
  delete>
  

  接口方法定义
  int deleteBatchData(List<Integer>listBatId);
  

  示例5：动态修改

  SQL映射配置
  <update id="updateAnswerRecord" parameterType="AnswerRecord">
  update answer_record 
  <set>
  <if test="respondent!=null">respondent=#{respondent},if>
  <if test="question!=null">question=#{question},if>
  <if test="rightAnswer!=null">right_answer=#{rightAnswer},if>
  <if test="submitAnswer!=null">submit_answer=#{submitAnswer},if>
  submit_datetime=now()
  set>
  where record_id=#{recordId}
  update>
  

  接口方法定义
  int updateAnswerRecord(AnswerRecord answerRecord);
  

  示例6：动态查询

  <select id="queryAllByCondition"  resultType="AnswerRecord" parameterType="AnswerRecord">
  SELECT  record_id AS recordId,
  respondent,
  question,
  right_answer AS rightAnswer,
  submit_answer AS submitAnswer,
  submit_datetime AS submitDatetime
  FROM answer_record
  
  <where>
  	<if test="respondent != null">AND respondent = #{respondent}if>
  	<if test="question != null">AND question LIKE concat('%',#{question},'%')if>	  <if test="rightAnswer != null">AND right_answer = #{rightAnswer}if>
  <if test="submitAnswer != null">AND submit_answer = #{submitAnswer}if>
  where>
  select>
  

  接口方法定义
  List<AnswerRecord> queryAllByCondition(AnswerRecord condition);
  

  示例7：查询结果封装为Map

  SQL映射配置
  <select id="countAnswerRecordDataByRespondent" resultType="map">
  	SELECT count(record_id) as total,
  		 (SELECT count(record_id) FROM answer_record WHERE respondent = #{name} AND right_answer = submit_answer ) as right_count,
  		 (SELECT count(record_id) FROM answer_record WHERE respondent = #{name} AND right_answer != submit_answer ) as fail_count
  	FROM answer_record
  	WHERE respondent = #{name}
  
  select>
  

  接口方法定义
  Map<String,Integer> countAnswerRecordDataByRespondent(String respondent);