在MyBatis中，可以使用Result注解來實現一對一映射。以下是一個示例：

首先，創建兩個實體類，一個是主實體類，一個是關聯實體類。

public class User {
    private Long id;
    private String username;
    private Profile profile;

    // getters and setters
}

public class Profile {
    private Long id;
    private String email;
    private String phone;

    // getters and setters
}

然后，在Mapper接口中定義查詢方法，使用Result注解來映射一對一關系：

public interface UserMapper {
    @Select("SELECT u.id, u.username, p.id as profile_id, p.email, p.phone FROM user u " +
            "LEFT JOIN profile p ON u.id = p.user_id WHERE u.id = #{id}")
    @Results({
        @Result(property = "id", column = "id"),
        @Result(property = "username", column = "username"),
        @Result(property = "profile.id", column = "profile_id"),
        @Result(property = "profile.email", column = "email"),
        @Result(property = "profile.phone", column = "phone")
    })
    User getUserById(Long id);
}

最后，在配置文件中配置Mapper接口和對應的SQL語句：

<configuration>
    <mappers>
        <mapper class="com.example.UserMapper"/>
    </mappers>
</configuration>

通過以上步驟，就可以實現一對一映射的查詢操作。在查詢User時，會自動查詢出對應的Profile信息，并將其映射到User實體類的profile屬性中。