Mybatis

Posted 2021-01-06 wu-zang

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Mybatis

MyBatis 本是apache的一个开源项目iBatis 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAOs）

MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

官方地址

简介使用

<!--全局配置文件 mybatis-config.xml-->
<?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>  
<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="org/mybatis/example/BlogMapper.xml"/>  
    <!-- 对应配置文件路径 * -->
</mappers> 
</configuration>

<!-- * org/mybatis/example/BlogMapper.xml -->
<?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="org.mybatis.example.dao.BlogMapper">  
<!-- 对应接口全类名位置 ## -->

<!-- 对应接口方法 ### -->
<select id="selectBlog" resultType="org.mybatis.example.bean.Blog">select * from Blog where id = #{id}</select> 

</mapper>

//## org.mybatis.example.dao.BlogMapper
public interface BlogMapper{
    // 对应mapper中方法 ###
    public Blog selectBlog(Integer id);
}

Mybatis底层与数据库交互是使用SqlSession完成的，SqlSession非线程安全，每次使用应当获取新对象，mapper接口的实现由mybatis生成一个代理对象。

public void test(){
  
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession session = sqlSessionFactory.openSession();
   try {  
           BlogMapper mapper = session.getMapper(BlogMapper.class);  
           Blog blog = mapper.selectBlog(1);  
   } finally {  session.close(); }    
}

全局配置文件

properties标签

<?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="db.properties" url="网络路径/本地路径"></properties>
  <!--resource:类路径   url：网络路径/本地路径 -->
  <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="${jdbc.username}"/>        
      <property name="password" value="${jdbc.password}"/>      
    </dataSource>    
  </environment>  
</environments> 
</configuration>

#db.properties
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mydql://localhost:3306/db
jdbc.username=username
jdbc.password=password

settings标签

<?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>  
  <settings>
    <setting name="mapUnderscoreToCamelCaseEnables " value="true" />
    <!-- 驼峰命民适配 -->
  </settings>
</configuration>

typeAliases标签

<?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>  
 <typeAliases>
    <typeAlias type="org.mybatis.example.bean.Blog" alias="blog"></typeAlias>
   <!-- mapper中就不用写全类名了，不写alias即默认为类名-->
  <package name="org.mybatis.example.bean"/>
   <!--当前包及其子包自动别名-->
  </typeAliases>
</configuration>

<?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="org.mybatis.example.dao.BlogMapper">  
<!-- blog 别名使用-->
<select id="selectBlog" resultType="blog">select * from Blog where id = #{id}</select> 
</mapper>

//通过@Alias注解使用别名
//批量扫描注解优先
@Alias("blog")
public class Blog{
  private Integer id;
  ...
}

Alias(默认别名)	Mapped Type
_long	long
_short	short
_int	int
_integer	int
_double	double
_float	float
_boolean	boolean
string	String
byte	Byte
long	Long
short	Short
int	Integer
integer	Integer
double	Double
float	Float
boolean	Boolean
date	Date
decimal	BigDecimal
bigdecimal	BigDecimal
map	Map

plugins插件

在四大对象执行前后进行拦截，原理为动态代理。

Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
ParameterHandler (getParameterObject, setParameters)
ResultSetHandler (handleResultSets, handleOutputParameters)
StatementHandler (prepare, parameterize, batch, update, query)

environments标签

<?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>  
  <environments default="development"> <!--指定默认使用环境来快速切换环境-->
    
        <environment id="env">
          <transactionManager type="JDBC"/> <!-- 事务管理器  type: JDBC|MANAGED 自定义 -->
        <dataSource type="POOLED">  <!-- 数据源配置 type：UNPOOLED|POOLED|JNDI 自定义-->
          <property name="driver" value="${oracle.driver}"/>        
          <property name="url" value="${oracle.url}"/>        
          <property name="username" value="${oracle.username}"/>        
          <property name="password" value="${oracle.password}"/>  
        </dataSource>
        </environment>
    
      <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="${jdbc.username}"/>        
          <property name="password" value="${jdbc.password}"/>      
        </dataSource>    
      </environment>  
    
</environments> 
</configuration>

databaseIdProvider标签

<?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>  
  <environments default="env">
    <databaseIdProvider type="DB_VENDOR">
    <property name="MySQL" value="mysql"/>
    <property name="Oracle" value="oracle"/>
    <property name="SQL Server" value="sqlserver"/>
  </databaseIdProvider>
</configuration>


<?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="org.mybatis.example.dao.BlogMapper">  
<!-- 发送带oracle的查询语句 -->
<select id="selectBlog" resultType="org.mybatis.example.bean.Blog">
        select * from Blog where id = #{id}</select> 
<select id="selectBlog" resultType="org.mybatis.example.bean.Blog" 
        databsesId="oracle">select * from Blog where id = #{id}</select> 
<select id="selectBlog" resultType="org.mybatis.example.bean.Blog" 
        databsesId="mysql">select * from Blog where id = #{id}</select> 
</mapper>

mapper标签

<!--全局配置文件 mybatis-config.xml-->
<?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>  
<mappers>    
  <mapper url=""></mapper>
  <!-- 磁盘路径 -->
  <mapper resource="org/mybatis/example/BlogMapper.xml"/>  
  <!-- 类路径 -->
  <mapper class="org.mybatis.example.dao.BlogMapperAnnotation"/>
  <!--1. mapper和接口 同名同路径-->
  <!--2. 添加注解方法的接口-->
  <package name="org.mybatis.example.dao"/>
  <!--  批量扫描 xml 接口 同包 -->
</mappers> 
</configuration>

//org.mybatis.example.dao.BlogMapperAnnotation
public interface BlogMapperAnnotation{
    // 对应mapper中方法 ###
    @Select("select * from Blog where id = #{id}")
    public Blog selectBlog(Integer id);
}

映射文件

CRUD

//## org.mybatis.example.dao.BlogMapper
public interface BlogMapper{
    // 对应mapper中方法 ###
    public Blog selectBlog(Integer id);
    public boolean insertdBlog(Blog blog);
    public Integer updateBlog(Blog blog);
    public boolean deleteBlog(Integer id);
  //自动返回 Integer 、Long、Boolean 类型
}

<!-- * org/mybatis/example/BlogMapper.xml -->
<?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="org.mybatis.example.dao.BlogMapper">  

<select id="selectBlog" resultType="org.mybatis.example.bean.Blog">
            select * from Blog where id = #{id}
  </select> 
  
<insert id="insertdBlog" parameterType ="org.mybatis.example.bean.Blog">
    insert into Blog...values(#{属性名}，#{属性名})
</insert>
  
<update id="updateBlog" parameterType ="org.mybatis.example.bean.Blog">
    update Blog set ... 字段 = #{属性名} where 字段 = #{属性名}
  </update>
  
<delete id="deleteBlog">
    delete from Blog where id = #{id}
  </delete>
  
</mapper>

获取自增主键

<!-- * org/mybatis/example/BlogMapper.xml -->
<?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="org.mybatis.example.dao.BlogMapper">  
  
  <!-- mysql 等支持 自增主键 数据库-->
<insert id="insertdBlog" parameterType ="org.mybatis.example.bean.Blog"
        useGeneratedKeys="true" keyProperty="#{id}" databaseId="mysql">
  <!-- 使用自增主键策略 插入数据库操作完成后原插入对象的id属性将被赋值-->
    insert into Blog...values(#{属性名}，#{属性名})
</insert>

  <!-- Oracle 从序列中获取 -->
<insert id="insertdBlog" parameterType ="org.mybatis.example.bean.Blog"
        databaseId="oracle">
    <selectKey KeyProperty="#{id}" order="BEFORE" resultTyoe"Integer">
    <!-- 使用查询序列 插入数据库操作完成后原插入对象的id属性将被赋值-->
    select Blog_sql.nextval from dual
  </selectKey>
    insert into Blog...values(#{id},#{属性名}，#{属性名})
  </insert>
  
</mapper>

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