Re: [Boost-users] [Multi-Index] New "hierarchical" indexing?

On Sat, Jul 11, 2009 at 5:17 AM, JOAQUIN M. LOPEZ MUÑOZ wrote:

...

In another use case, entries have a "scenario" key, where scenario is hierarchical, and I want all entries in BMI A from a given scenario and all its ancestors, with the scenarios being in BMI B (i.e. "cross-bmi"). Of course I can do a "full scan" but I'm looking for something hopefully faster/smarter.

Not entirely sure if the following is directly applicable to your problem, but anyway.

Thank you for taking the time to provide a full exemple. That's really nice!

 typedef multi_index_container<    entry,    indexed_by<      ordered_non_unique >    >  > entry_container_t;

I'm currently using hashed indices only. Does the technique of using a compatible key extend to them? (I suspect not in this case, but I thought I'd ask, just in case I'm misunderstanding.)

What is this? parent_t is just a sort of alias to scenario_t that allows us to differentiate between a "terminal" scenario and a scenario used for purposes of recursive lookup. children is a compatible (with the order of entry_container_t) compare predicate that levels off scenario paths in a way that, for instance, if we have parent "a" then "a/b", "a/d", "a/b/e" etc. are deemed equivalent to the parent.

I was thinking about such a Materialized Path impl, after reading http://www.dbazine.com/oracle/or-articles/tropashko4 recently. But I would not have been able to express it in an example as easily as you could. I appreciate the leg up.

Is this of any help to your particular problem?

I think it does. I'll need time to digest and adapt it, but it sounds like Materialized Path with an ordered index will avoid a full scan. Thanks again for your help. --DD