mybatis注解开发
MyBatis中使用@Results注解来映射查询结果集到实体类属性。
（1）@Results的基本用法。当数据库字段名与实体类对应的属性名不一致时，可以使用@Results映射来将其对应起来。
column为数据库字段名，porperty为实体类属性名，jdbcType为数据库字段数据类型，id为是否为主键。
@Select("select * from orders where id=#{id}")
@Results({
@Result(id=true,column = "id",property = "id"),
@Result(column = "orderNum",property = "orderNum"),
@Result(column = "orderTime",property = "orderTime"),
@Result(column = "orderStatus",property = "orderStatus"),
@Result(column = "peopleCount",property = "peopleCount"),
@Result(column = "payType",property = "payType"),
@Result(column = "orderDesc",property = "orderDesc")
})
Orders findById(String id) ;
（2）@ResultMap的用法。当这段@Results代码需要在多个方法用到时，为了提高代码复用性，我们可以为这个@Results注解设置id，然后使用@ResultMap注解来复用这段代码。
@Select({"select id, name, class_id from my_student"})
@Results(id="studentMap", value={
@Result(column="id", property="id", jdbcType=JdbcType.INTEGER, id=true),
@Result(column="name", property="name", jdbcType=JdbcType.VARCHAR),
@Result(column="class_id ", property="classId", jdbcType=JdbcType.INTEGER)})List selectAll();
@Select({"select id, name, class_id from my_student where id = #{id}"
})
@ResultMap(value="studentMap")
Student selectById(integer id);
（3）@One的用法。当我们需要通过查询到的一个字段值作为参数，去执行另外一个方法来查询关联的内容，而且两者是一对一关系时，可以使用@One注解来便捷的实现。
其中column对应的值在传入select时，不管是设置为memberId还是id都可以传入使用，建议设置为memberId，提高可读性。
@Select("select * from orders where id=#{id}")
@Results({
@Result(id=true,column = "id",property = "id"),
@Result(column = "orderNum",property = "orderNum"),
@Result(column = "orderTime",property = "orderTime"),
@Result(column = "orderStatus",property = "orderStatus"),
@Result(column = "peopleCount",property = "peopleCount"),
@Result(column = "payType",property = "payType"),
@Result(column = "orderDesc",property = "orderDesc"),
@Result(column = "memberId",property = "member",
one = @One(select = "findById"))
})
Orders findById(String id) ;
@Select("select * from member where id=#{memberId}")
Member findById(String id) throws Exception;
（4）@Many的用法。与@One类似，只不过如果使用@One查询到的结果是多行，会抛出TooManyResultException异常，这种时候应该使用的是@Many注解，实现一对多的查询。
其中column对应的值在传入select时，不管是设置为id还是orderId都可以传入使用，建议设置为id，提高可读性。
@Select("select * from orders where id=#{id}")
@Results({
@Result(id=true,column = "id",property = "id"),
@Result(column = "orderNum",property = "orderNum"),
@Result(column = "orderTime",property = "orderTime"),
@Result(column = "orderStatus",property = "orderStatus"),
@Result(column = "peopleCount",property = "peopleCount"),
@Result(column = "payType",property = "payType"),
@Result(column = "orderDesc",property = "orderDesc"),
@Result(column = "id",property = "travellers",many = @Many(select = "findByOrdersId"))
})
Orders findById(String id) throws Exception;
@Select("select * from traveller where id in (select travellerId from order_traveller where orderId=#{id})")
/*@Select("select * from traveller where id in (select travellerId from order_traveller where orderId=#{orderId})") 都可以使用*/
public List findByOrdersId(String ordersId) throws Exception;
