Re: [Boost-users] [multi-index] Key extractor for 1:n relationship?

Subject: Re: [Boost-users] [multi-index] Key extractor for 1:n relationship?
From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2009-07-17 10:14:39

Boris Schaeling <boris <at> highscore.de> writes:

> 
> All the key extractors in the documentation of Boost.MultiIndex return one  
> value for an element in a container. Is it somehow possible to use a 1:n  
> relationship between element and value?
> 
> The documentation uses this container definition (among others):
> 
> typedef multi_index_container<
>    employee,
>    indexed_by<
>      hashed_unique<
>        const_mem_fun<employee, std::string, &employee::name>
>      >
>    >
> > employee_set;
> 
> Let's assume an employee can have more than one name (std::string becomes  
> std::vector<std::string>). Now if someone searches for Tom or John the  
> same employee should be returned by the container. Is this possible?

No, I don't think it's possible in general. Take into account
that when you insert an element x into a multi_index_container
m, then x will appear exactly once when traversing any
index of m. So if you want something like multiple retrieval
within one index you'd have to insert x multiple times. I'm
afraid you'll need a separate container to hold this
1:n relationship.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo