[Glass] There is really no way to have an ordered/sorted collection together with indexes?

[Mariano Martinez Peck via Glass]

On Mon, Aug 7, 2017 at 5:04 PM, Richard Sargent via Glass <
glass at lists.gemtalksystems.com> wrote:

> GLASS mailing list wrote
> > Hi guys,
> >
> > I am storing huge lists of "prices". For this, it really helps me to
> store
> > things ordered (by date)...either in an SequenceableCollection or a
> > SortedCollection. On the other hand, I do want to use indexes to speedup
> > my
> > query to find price for a given date (equality index).
> >
> > But I have found no way to have them both. The only workaround I found is
> > to keep 2 collections for each of these collections, one sorted/ordered,
> > and the other one an unordered one for querying via index. But this is a
> > pain from "developing" point of view, as well as for unnecessary
> > repository
> > growth.
> >
> > Am I missing something?
>
> Mariano, have you read chapter 7 in the GemStone/S 64 Programming Guide?
> It's all about indexing.
>
> It looks like you could define a "range" query over the unordered
> collection
> to get the sorted sequence needed to traverse all the prices in date order.
> The index would be on the date and the range query would be from some
> "least
> date" through some "greatest date". You would then use the streaming
> results
> or the #do: message I think) to iterate over the query result in date
> order.
> There is a section in chapter 7.2 discussing result order.
>
>
>
Hi Richard,

Thanks for such a pointer. And no, I wasn't aware of that kind of range
query. I will read it as soon as I am back or tomorrow first thing in the
morning. In the meanwhile, I will quickly answer your below question.


> It might be helpful to discuss the use cases for the two collections. When
> would you iterate over all the dates versus when would you search for
> specific dates or ranges of dates?
>
>
I need to support 2 kinds of getting a price from a security:

1) Get the price for given date X and if not found, answer nil.
2) Get the price for a given date X but it it wasn't found, find the
closest (but older) one. Kind of "please gave me the latest price you can
for this date"

1) can simply call 2) and check if the date answer is the same as the
original. However, I want 1) to be as fastest as possible, meaning I may
not want to use 2) directly.  So far, I was trying this kind of code which
obviously doesn't work because I cannot have collection both sorted and
with index, but this was the idea anyway:

prices := self storageDict at: securityUniqueId ifAbsent: [ nil ].
(prices notNil and: [ prices notEmpty ]) ifTrue: [
onOrBeforeMatching
ifTrue: [
| exactPrice closest |
exactPrice := prices detect: (DpDatabaseQueryClosureBuilder current
selectClosurePriceRecordByDate: dateToCompare) ifNone: [ nil ].
exactPrice
ifNil: [
closest := prices first.
                                                "we know prices are
sorted.."
prices do: [ :each |
(each date > dateToCompare) ifTrue: [
^ (closest date <= dateToCompare) ifTrue: [ closest ] ifFalse: [ nil ]
].
closest := each.
].
^ (closest date <= dateToCompare) ifTrue: [ closest ] ifFalse: [ nil ].
]
ifNotNil: [ ^ exactPrice ]
]
ifFalse: [
^ prices detect: (DpDatabaseQueryClosureBuilder current
selectClosurePriceRecordByDate: dateToCompare) ifNone: [ nil ].
]
].
^ nil



DpDatabaseQueryClosureBuilder  answers those magic search block for the
indexes....
The boolean onOrBeforeMatching is the one that defines either behavior 1)
or 2).
My idea was simple. For 1) use the query for the date index. For 2) use
also same query and only if it answers nothing, then iterate collection.
Sure, I can replace that iteration with a binary search too. But again, all
this doesn't work ...


Hope this helps clarifying my questions...

Thanks a lot in advance,



>
> > Thanks in advance,
> >
> > --
> > Mariano
> > http://marianopeck.wordpress.com
> >
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>
>
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>
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> is-really-no-way-to-have-an-ordered-sorted-collection-
> together-with-indexes-tp4959121p4959135.html
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-- 
Mariano
http://marianopeck.wordpress.com
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