02-MyBatis的SQL映射文件的配置

XxxxMapper.xml:专门用来编写SQL语句的映射文件(一个表对应一个),如t_user表一般会对应一个UserMapper.xml

`mapper的namespace属性`

如果两个SQL映射文件中的sqlid重名,My bat is无法确定执行哪个SQL语句会提示sqlid在集合中不明确(请尝试使⽤包含名称空间的全名或重命名其中⼀个条⽬)

在mybatis-config.xml核心配置文件中引入CarMapper.xml和CarMapper2.xml

&lt;!--引入sql映射文件--&gt;
&lt;mappers&gt;
    &lt;mapper resource="CarMapper.xml"/&gt;
    &lt;mapper resource="CarMapper2.xml"/&gt;
</mappers>

CarMapper.xml和CarMapper2.xml两个SQL映射文件中都有 id="selectCarAll"的SQL语句,但是它们的namespace前缀不相同MyBatis可以区分

<!--CarMapper.xml-->
<mapper namespace="car">
     <select id="selectCarAll" resultType="com.powernode.mybatis.pojo.Car">
        select
            id, car_num as carNum, brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType
        from
            t_car
     </select>
</mapper>

<!--CarMapper2.xml-->
<mapper namespace="car2">
     <!--sqlid重名了-->
     <select id="selectCarAll" resultType="com.powernode.mybatis.pojo.Car">
        select
            id, car_num as carNum, brand, guide_price as guidePrice, produce_time as produceTime, car_type as carType
        from
            t_car
     </select>
</mapper>

执行SQL语句使用SQL映射文件中的命名空间作为sqli d的前缀

@Test
public void testNamespace(){
    // 获取SqlSession对象
    SqlSession sqlSession = SqlSessionUtil.openSession();

    // 执⾏SQL语句时的完整写法namespace.id
    List<Object> cars = sqlSession.selectList("car.selectCarAll");
    List<Object> cars = sqlSession.selectList("car2.selectCarAll");

    // 输出结果
    cars.forEach(car -> System.out.println(car));
}