1.首先就是配置文件
<?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>
<!-- 为实体取个别名 -->
<typeAliases>
<typeAlias type="类的完全限定名" alias="别名"/>
<!-- 也可以通过配置包的方式让mybatis自动为该包下的每个类以冠以该类的名称-->
<package name="com.qfedu.mybatis.entity"/>
</typeAliases>
<environments default="development">
<environment id="development">
<!-- type可以为MANAGED交给web容器进行管理 -->
<transactionManager type="JDBC" />
<!--
也可以配置JNDI
< dataSource type ="JNDI" >
< property name ="DataSource" value ="java:comp/env/jdbc/myDataSource" />
</ dataSource >
-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8" />
<property name="username" value="root" />
<property name="password" value="ily" />
</dataSource>
</environment>
</environments>
<!-- 配置映射文件 -->
<mappers>
<!-- 包级别的路径 -->
<mapper resource="com/qfedu/mybatis/entity/UserMapper.xml" />
</mappers>
</configuration>
2.然后是Mapper
<?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.qfedu.mybatis.dao.UserDao">
<!-- 结果映射，如果名字和数据库是意义对应的话可以不用写 id，result等等，但要写的话必须每个字段都要意义对应，且全部都要写 -->
<resultMap id="UserResult" type="User" >
<!-- id映射 -->
<id property="id" column="userId"/>
<!-- 以下为属性映射 -->
<result property="username" column="username"/>
<result property="password" column="password"/>
<!-- 容器映射 ofType:容器元素的类型,也可以引用另一个resultMap -->
<collection property="orders" ofType="Order">
<id property="id" column="orderId"/>
<result property="time" column="time"/>
<result property="money" column="money"/>
</collection>
</resultMap>
<!--
以下配置sql语句 parameterType：参数类型， resultType:返回结果类型 #{}：使用和EL表达式差不多
例如#{username}相当于parameterType中的username属性
-->
<delete id="delete" parameterType="User">
delete from tb_user where username = #{username}
</delete>
<select id="findAllUser" resultMap="UserResult">
select u.*, o.* from tb_user as u left join tb_orders as o on u.userId = o.userId
</select>
<select id="findById" parameterType="java.lang.Integer" resultType="User">
select u.*, o.* from tb_user as u, tb_orders as o where u.id = #{id} and u.userId = o.userId
</select>
<insert id="save" parameterType="User">
insert into tb_user values(default, #{username}, #{password})
</insert>
</mapper>
3.代码部分
public class User implements Serializable {
private static final long serialVersionUID = 1L;
private Integer id;
private String username;
private String password;
private List<Order> orders;
//省略getter和setter
}
public class Order implements Serializable {
private static final long serialVersionUID = 1L;
private Integer id;
private Date time;
private BigDecimal money;
}
public class Test {
public static void main(String[] args) throws IOException {
//获取配置文件内容
InputStream inputStream = Resources.getResourceAsStream("com/qfedu/mybatis/mybatis-config.xml");
//通过配置文件创建SqlSessionFacroty
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
try {
UserDao userDao = session.getMapper(UserDao.class);
List<User> user = userDao.findAllUser();
session.commit();
} finally {
session.close();
}
}
}
总结：在学习mybatis的过程中，有一点特别注意，数据库的主键（一般是id）一定不要相同，加上前缀加以区分，否则mybatis查询时数据会遗漏。
