Chuck,
On 15. 2. 2015, at 1:56, Chuck Hill <[email protected]> wrote:
> === my EO code ===
> public NSArray orderedPriceOffers {
> NSArray offers=priceOffers() // this is a modelled relationship
> if (offers==null || offers.count<2) return offers
> try {
> offers=offers.sortedArrayUsingComparator(new OCSDateComparator())
> } catch (Exception exc) {
> ... never happens anyway, no need to show ...
> }
> return offers
> }
> public DBPriceOffer lastValidPriceOffer {
> NSArray a=orderedPriceOffers()
> if (a==null || a.count==0) return null
> for (int n=a.count-1;n>=0;n--) {
> DBPriceOffer po=(DBPriceOffer)a.objectAtIndex(n)
> if (po.validOffer()) // this is a modelled boolean attribute
> return po
> }
> return null
> }
> ...
> @OCStandard class OCSDateComparator extends NSComparator {
> public int compare(Object left,Object right) {
> DBPriceOffer l=(DBPriceOffer)left,r=(DBPriceOffer)right
> return l.creationDate().compare(r.creationDate()) // modelled
> timestamp attribute, always set creation-time
> }
> }
> ===
>
> It would be very beneficial to speed up orderedPriceOffers,
>
> To speed up lastValidPriceOffer or for some other reason?
It is used elsewhere too, and although it is not that pressing as
lastValidPriceOffer (which is used at more places), it would help to speed it
up, too.
> I am assuming this is a large list.
Alas, it is. When written and tested years ago, there used be tens of items
max; today they use the code with thousands of items, and that's a big problem
which I have to solve ASAP :)
> You could sort and cache on the EO and invalidate the cache if the
> relationship changes. Sorting at the database is usually faster, especially
> if there is a usable index.
This is precisely what I don't know howto, can you help? I found no way to
force the SELECT caused by firing a relationship fault to use any ORDER BY.
Or do you suggest that I don't use a modelled relationship at all, implementing
something like
=== [*]
private cache
def orderedPriceOffers {
if (cache) return cache
cache=this.editingContext.objectsWithFetchSpecification( yadda yadda incl sort
orderings )
}
def addPriceOffer {
cache=nil
...
}
===
I thought caching objects this way was an extremely big no-no? Besides even at
the first look I can see lots of possible catches and gotchas, with different
ECs, with objects inserted but not-yet-saved, etc...
>> and it is a must to speed up lastValidPriceOffer -- very considerably,
>> preferrably to O(1) if possible.
> I’d model a to-one and update this when the priceOffers relationship changes.
Hmmm... actually, does this differ anyhow from caching the GID? (Save for the
first access, for cached GID is not stored in the DB, and thus forces search
once.)
A to-one is simply cached PK, stored in DB, or am I overlooking something?
>> Note that the price offers are always sorted by their creation date -- never
>> otherwise --, which effectively means new objects are always added to the
>> end of the sorted array, never ever inserted. Also, price offers are not
>> editable; once stored, they never change, both validOffer and creationDate
>> attributes stay unchanged forever (other ones too, which is irrelevant here).
>>
>> It seems to me, given this business logic, it would be best
>> - to fetch the fault using a sort ordering, to ensure it fetches
>> appropriately ordered
>> - whenever a new object is added to an already fetched relationship, to add
>> it to the end of the array the EO stack maintains.
>>
> Except that, as you note below, relationships in EOF are unordered sets. EOF
> makes no guarantees about maintain an ordering in the relationship.
Well there must be _some_ reason they used NSArrays instead of NSSets I guess.
> Don’t fight EOF. Un-ordered set are un-ordered sets.
Anyway, I don't really want to fight EOF; rather I would co-operate with it to
get the best result.
In this case the best result would be
(a) to fetch sorted with ORDER BY into an array
(b) to add newly created objects to the end of the array
Seems to me somewhat too far at the ubiquitous side for EOF/Wonder not to
support anything remotely similar and leaving me completely on me own with
something like [*]? But perhaps it's just the way the things are :)
>> As for lastValidPriceOffer, I tried to cache the object's permanentGlobalID
>> when found or added new valid one (caching the object itself failed with
>> different ECs), but it still does not work well, and is terribly ugly and
>> error-prone.
> Why not just model it? It is a real thing.
Well I sort of never thought of that :)
That aside, for this app it is somewhat inconvenient to change the DB schema.
For the next release I will do that.
Thanks a lot,
OC
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