@Results 注解

• **作用：**用于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。
• @Result 属性：
  1. column为数据库字段名
  2. porperty为实体类属性名
  3. jdbcType为数据库字段数据类型
  4. javaType为Java类的类型
  5. id为是否为主键
• 举例展示：

@Select("select * from student where sid = 1 ")
    @Results({
            @Result(property = "sid",column = "sid"),
            @Result(property = "name",column = "name"),
            @Result(property = "sex",column = "sex"),
            @Result(property = "age",column = "age"),
    })
    Student getStudentInfo();

@One 注解 与 @Many注解

• 注解作用：
  • @One：用于实现一对一关系的联合查询，可以将某个查询中的字段当做新的条件，去进行子查询并返回单一对象。
  • @Many：用于实现一对多关系的联合查询，也可以将某个查询字段当做子查询的条件，但允许子查询返回多个对象。
• 常用共同属性：
  • select：用于指定用于子查询的是哪个查询，其后无需跟属性参数以及类型，包含方法名即可。
  • fetchType：有三个值，分别对用立即加载，延迟加载和默认。
• @One注解 举例说明：

@Select("select * from borrow where id = #{id}")
    @Results({
          @Result(id = true,property = "id",column = "id"),
          @Result(property = "student",column = "sid",one = @One(select = "getStudentInfo")),
          @Result(property = "book",column = "bid",one = @One(select = "getBookInfo")),
          @Result(property = "date",column = "date")
    })
    Borrow getBorrowInfo(int id);

// student 子查询
@Select("select * from student where sid = #{sid}")
    @Results({
            @Result(property = "sid",column = "sid"),
            @Result(property = "name",column = "name"),
            @Result(property = "sex",column = "sex"),
            @Result(property = "age",column = "age"),
    })
    Student getStudentInfo(int sid);

// book 子查询
@Select("select * from book where bid = #{bid}")
    @Results({
            @Result(property = "bid",column = "bid"),
            @Result(property = "title",column = "title"),
            @Result(property = "desc",column = "desc"),
            @Result(property = "price",column = "price"),
    })
    Book getBookInfo(int bid);