LOL!! Your first assertion : "btw, i don't really get what is the problem with subselect" Your second assertion : "the sub select is always inefficient"
On Wed, Sep 1, 2010 at 1:42 PM, nadav s <[email protected]> wrote: > the sub select is always inefficient, especially when there is an initial > complex query (with sub queries in it), and its a killer when its a two > level tree (when fetching the grandchildren). fixing it was really really > easy, and i can't see any downside to it. > > different use cases in a web app: > > use case 1: sub select\batch size is NOT desired > > the user searches for car companies by some criteria. the user will then > choose (double click on a grid's row or something) one of the > companies to see it in full details. each company has one-to-many car > types (mazda -> mazda 3, mazda 5, mazda 6...) and each > car type will be displayed in its own tab, when at first, the newest car > type or the most expensive one, doesn't matter is selected. > each car type has its models, mazda3 2008 isn't the same as 2010 (i > don't that much about cars and not sure the years are correct, > but there are differences between the models). > > the result: if carType.Models is mapped with some batch size, say 10, > the models of 10 of the car types are now fetched, although > the user only watches the models of one of the car types, if there could > be lots of models for each car type, it slowed the first tab, > and made the other tabs faster, because their car types are now loaded, > but its not what is desired, because the user is expected to > click on only one of other tabs or something. > > use case 2: desired: > > the user wanna see some custom developed report (ui that can be > implemented with MRS/Cognus or any other reporting framework, > and we have all kinds of reports that live up to this definition, and > for some good reasons also). for the report the user searches for > car companies by some criteria (some search form) and then expects to > see the returned companies, paged of course, but with all > of their car types, and for each of the car type - all of its models. > here, a sub select or batch fetching is a must or else we'll get a CP > with join fetching, or N^2 + 1 if we do regular lazy loading (like we > wanted to do in the first situation). > > of course we can work around that, and thats exactly what we do, using a > generic mechanizm that for reports, eager fetches with sub selects and not > joins, the association it was asked to fetch. for the regular queries, it > just use the default which is regular lazy. > > it would have been really really nice, if i could have set, for the report > query, query.SetFetchMode("CarTypes", FetchMode.SubSelect) > or if you will, query.SetBatchSize("CarTypes", 20) > and same for models > query.SetFetchMode("CarTypes.Models", FetchMode.SubSelect) or > query.SetBatchSize("CarTypes.Models", int.MaxValue). > > it must be max value because i want all the models, and can't possibly know > how many car types are going to be there. of course it won't be alot, > because the "query" is going to use paging, but i don't really know if its > 20, 40, or something else. > > batch size, currently makes me choose between the use cases, slowing down > one of them, or makes me query and connect the associations my self. same > goes for sub select, which also issues an inefficient query for CarTypes and > a killer query for the Models > before my fix it would have been: > select ... > from Models m > where m.CarTypeId in > (select c.Id > from CarTypes c > where c.CompanyId in > (select company.Id > from Companies company > where <could be some crazy crteria - this is the same where > clause of the very original query>)) > > > > (i was able to make itthe inefficiency of the query > > > > > On Wed, Sep 1, 2010 at 6:58 PM, Fabio Maulo <[email protected]> wrote: > >> I don't know which is the problem... you said that there is a problem and >> you want change it using the same tech used by batch-size (using uploaded >> ids) because subselect seems inefficient in some cases. >> >> >> On Wed, Sep 1, 2010 at 12:48 PM, nadav s <[email protected]> wrote: >> >>> btw, i don't really get what is the problem with subselect, as it lets >>> you efficiently fetch a whole object graph for the N fathers that were >>> fetched in some query, in the most efficient way possible >>> >>> >>> On Wed, Sep 1, 2010 at 6:46 PM, nadav s <[email protected]> wrote: >>> >>>> i don't think its thats low priority, because it is actually a thing >>>> people expect to happen when they set a fetch mode to Eager, at least i've >>>> seen alot of situations when people really thought that thats whats going >>>> to >>>> happen (later finding out it killed their query with CP) >>>> >>>> about when it is helpful - exactly in the situations diego described. >>>> two use cases, >>>> in one of them you query the fathers and gonna need only one of the >>>> father's collection, and for the other >>>> you're gonna need all of their collections. >>>> it gets more complicated when there are grandchildren involved, and in >>>> one of the situations you want the grand children of one of the childs, and >>>> in the other situation, because you load an object graph, you're gonna need >>>> all of them. >>>> >>>> now, either you implement (similar to what diego said) the loading of >>>> the collections yourself, or you gonna have to live with the batch size >>>> slowing down the first situation, where you would have prefered lazy >>>> loading >>>> without batching >>>> >>>> >>>> On Wed, Sep 1, 2010 at 5:22 PM, Diego Mijelshon <[email protected] >>>> > wrote: >>>> >>>>> I have entities where batch loading helps in some use cases but it >>>>> loads lots of unneeded entities/collections in other complex use cases, >>>>> where I have many proxies but only use a few. >>>>> My current workaround is doing "manual batch loading" (i.e. dummy >>>>> query) in the cases where I need it. >>>>> >>>>> It would be definitely a low-priority but nice-to-have feature. >>>>> >>>>> Diego >>>>> >>>>> >>>>> >>>>> On Wed, Sep 1, 2010 at 10:12, Fabio Maulo <[email protected]>wrote: >>>>> >>>>>> It is possible for batcher (INSERT, UPDATE,DELETE). >>>>>> I don't understand where it is useful for collection/relations >>>>>> batch-size. >>>>>> >>>>>> >>>>>> On Wed, Sep 1, 2010 at 9:37 AM, Diego Mijelshon < >>>>>> [email protected]> wrote: >>>>>> >>>>>>> Being able to override batch-size would be useful. Implementing it >>>>>>> requires messing with more than one part of the infrastructure, though. >>>>>>> >>>>>>> Diego >>>>>>> >>>>>>> >>>> >>> >> >> >> -- >> Fabio Maulo >> >> > -- Fabio Maulo
