Mybatis流程

Mybatis

• 善用官方文档

  • 用Maven创建项目，导入依赖

    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>x.x.x</version>
    </dependency>
    

  • 写接口BlogMapper，写类Blog，配置mysql、junit、log4j等

  • log4j有一个配置文件，提供日志功能，执行步骤

    # Global logging configuration
    log4j.rootLogger=DEBUG, stdout
    # Console output...
    log4j.appender.stdout=org.apache.log4j.ConsoleAppender
    log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
    log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
    

  • 每个基于 MyBatis 的应用都是以一个 SqlSessionFactory 的实例为核心的。构建SqlsessionFactory（在测试类中编写）

    String resource = "org/mybatis/example/mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    

  • 配置XML，与数据库的连接

    <?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="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/run2?useSSL=false&amp;serverTimezone=UTC"/>
                    <property name="username" value="root"/>
                    <property name="password" value="ssss1998"/>
                </dataSource>
            </environment>
        </environments>
        <mappers>
            <mapper resource="dao/Mapper.xml"/>
        </mappers>
    </configuration>
    

  • 写相应的映射项，例子（类Student、接口Studentdao）

    <?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.shaon.Studentdao">
        <select id="selectallstudent" resultType="com.shaon.Student">
            select * from student
        </select>
    </mapper>
    

  • 从SqlsessionFactory获取Sqlsession（在测试类中编写）

    try (SqlSession session = sqlSessionFactory.openSession()) {
      BlogMapper mapper = session.getMapper(BlogMapper.class);
      Blog blog = mapper.selectBlog(101);
    }
    

  • 使用resultMap要注意：
    Colum的值要和数据库中的列名一样!!!!（如果不一样就查询不到），当映射的类的属性名和数据库的列名不一致时这么做。这个操作用来解决类中的属性名和数据库中的列名不一致的情况

     <resultMap id="studentResultMap" type="com.shaon.Student">
         <id property="id" column="ID"/>
         <!--""里面的值不能留空格        -->
         <result property="student_name" column="name"/>
         <result property="dept" column="dept_name"/>
         <result property="cred" column="tot_cred"/>
         <result property="birth" column="birthday"/>
     </resultMap>
    

  • as之前的是数据库列名

  <select id="selectUsers" resultType="User">
   select
     user_id             as "id",
     user_name           as "userName",
     hashed_password     as "hashedPassword"
   from some_table
   where id = #{id}
  </select>