Mybatis(四) 注解

最新推荐文章于 2025-08-27 15:02:00 发布

原创最新推荐文章于 2025-08-27 15:02:00 发布 · 186 阅读

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本文详细介绍MyBatis注解的使用方法，包括增删改查基本操作、复杂查询及多对多关系处理。通过具体代码示例，展示如何利用注解实现数据库操作，为开发者提供实用的参考。

Mybatis的注解们
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用例：

 @Insert("INSERT INTO student(name,math,eng) VALUES (#{name},#{math}, #{eng})")
    void insert(Student student);

    @Delete(" delete from student where id=#{id}")
    void delete(int id);

    @Update("update student set name=#{name}, math=#{math}, eng=#{eng} where id =#{id}")
    void update(Student student);

    @Select(" select * from student where id=#{id}")
    Student findByID(int id);

Results 、Result

 @Select("select *,o.uid as UserID ,o.id as OrderID from user as u inner join orders as o on o.uid=u.id order by u.id")
    @Results({
            @Result(column = "OrderID",property = "id"),
            @Result(column = "ordertime",property = "ordertime"),
            @Result(column = "total",property = "total"),
            @Result(column = "UserID",property = "user.id"),
            @Result(column = "name",property = "user.name"),
            @Result(column = "password",property = "user.password")

    })
    List<Order> findAll();

基于注解的多对多查询
思路就是分两步查询，查出User表中所有用户，然后再使用用户的id去和中间表和role表联查，将结果封装在User的ROLElIST中。详见下：
UserMapper接口

 @Select("select * from user")
    @Results({
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "name",property = "name"),
            @Result(column = "password", property = "password"),
            @Result(
                    property = "RoleList",//放到哪里，即user类中的哪个属性
                    column = "id",//拿谁去查,就是用userID传参
                    javaType = List.class, //该属性的类型
                    //一对一就是@One，一对多就是@Many
                    many = @Many(select = "com.dao.RoleMapper.findByUID")//调用其他查询方法，该方法需要传入int id的参数
            )
    }

    )
    List<User> findUserAndRole();

RoleMapper

 @Select("select * from role_user as ru,role as r where ru.roleid=r.id and ru.userid=#{id}")
    List<Role> findByUID(int id);

测试结果如下：
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