I don't see how catching _some_ errors statically is "useless". The constraint for non-generic IEnumerable is more expressive too, and costs nil.
From: [email protected] [mailto:[email protected]] On Behalf Of Diego Mijelshon Sent: Friday, September 03, 2010 1:41 PM To: [email protected] Subject: Re: [nhibernate-development] implementing FetchMode.SubSelect per query, and improving it You are right. Since the validation is useless, you can just use Func<T, object>, like ConfORM Diego On Fri, Sep 3, 2010 at 08:04, Frans Bouma <[email protected]<mailto:[email protected]>> wrote: Beware of IEnumerable: 'string' also implements IEnumerable, so c=>c.CompanyName will also match, while it's not a collection ;) FB > changed the object to ienumerable, still wondring about the argument > exception there, weather this is correct > > > On Fri, Sep 3, 2010 at 1:47 PM, nadav s > <[email protected]<mailto:[email protected]>> wrote: > > > done but i'm not sure i did it correctly as i never had to proccess a > linq expression... > > is this right? > > public void SetFetchingBatchSize<TEntity>(Expression<Func<TEntity, > object>> association, int batchSize) > { > if (!(association is LambdaExpression) || > !(association.Body is MemberExpression)) > { > throw new ArgumentException("Batch size can only be > set by a lambda expression which returns a member association"); > } > > > this.SetFetchingBatchSize<TEntity>(ExpressionProcessor.FindMemberExpression( > association.Body), batchSize); > } > > > On Fri, Sep 3, 2010 at 5:44 AM, Diego Mijelshon > <[email protected]<mailto:[email protected]>> wrote: > > > Nice job! > > How about a strongly-typed version of the collection ones? > > > void SetFetchingBatchSize<TEntity>(Expression<Func<TEntity, > IEnumerable>> association, int batchSize); > > > Allowing: > > > session.SetFetchingBatchSize<Father>(f => f.Children, 5); > > Diego > > > > On Thu, Sep 2, 2010 at 20:17, nadav s > <[email protected]<mailto:[email protected]>> > wrote: > > > NH-2316 <http://216.121.112.228/browse/NH-2316> > although the name of the jira is subselect, the actual > patch lets a developer set the batch size for an entity\collection > overriding the settings in the mappings. > > looking forward for comments\application of the patch. > > thanks alot. > > On Thu, Sep 2, 2010 at 6:52 PM, nadav s > <[email protected]<mailto:[email protected]>> wrote: > > > its much more pretty that what needs to be done > now to achive the same result > > > On Wed, Sep 1, 2010 at 9:48 PM, Fabio Maulo > <[email protected]<mailto:[email protected]>> wrote: > > > Ups sorry you have already included the > option for collection... > As you can see, nadav, the work to do in > each UoW will be pretty ugly than the batch-size by default in the > mapping... > I would see how you will manage it in > your application where, hopefully, the session is managed in a generic way > not depending on a specific use-case. > > > On Wed, Sep 1, 2010 at 3:42 PM, Fabio > Maulo <[email protected]<mailto:[email protected]>> wrote: > > > Not enough... it should allow the > batch-size per collection (property-path) not only per-class. > > > On Wed, Sep 1, 2010 at 3:19 PM, > Diego Mijelshon <[email protected]<mailto:[email protected]>> wrote: > > > If you do implement a > customizable batch-size, it should be per-session... > Something like the existing > SetBatchSize and EnableFilter... > > A possible API: > > > session.EnableBatching(typeof(Foo), 100); //on Foo entity > > session.EnableBatching(typeof(Foo), "Bars", 50); //on the Foo.Bars > collection > > session.EnableBatching("Foo.Bars", 50); //alternative > > session.DisableBatching(...); //with the same options > > Diego > > > > On Wed, Sep 1, 2010 at > 14:38, nadav s <[email protected]<mailto:[email protected]>> wrote: > > > of course i'll be > doing the same work as batch size, i'm not set to implement batch size all > over again, but trying to allow it to be query specific, meaning, being able > to look for owners of a specific query, and not all owners that are in the > session (owners from different query might be there), and allowing it to be > overrideable > > > On Wed, Sep 1, 2010 > at 8:09 PM, Fabio Maulo <[email protected]<mailto:[email protected]>> > wrote: > > > ah... > take care with > "using IDs is more efficient" because "subselect" does not suffer the > problem of max-parameter (IIRC 2100 in msSQL) > > > On Wed, Sep 1, > 2010 at 2:03 PM, nadav s <[email protected]<mailto:[email protected]>> > wrote: > > > great. > thanks > > > On Wed, > Sep 1, 2010 at 7:56 PM, nadav s > <[email protected]<mailto:[email protected]>> wrote: > > > > you know the internal of nhibernate much much much better than me, > and i won't get into an implementation argue with you, but it is possible to > implement. > > > with subselect (again i'm talking about subselect because i didn't do > any research on the batch size, but i guess the idea is similar because it > works the same, only batch size issues a good query and subselect issues an > evil one), as i've noticed, there is a special one-to-many collection > persister, that knows once the collection is accessed, use a sub select > batcher that loads the collections of all the owners that were returned by > the initial query. > > > if the persister could have been set, or modified, for a specific > instance of a collection, it would have been possible - you could have set > the batch size\subselect for a specific query, which in turn would have set > a different persister for the collections that their persisters needs > modification, and then when a collection would have been accessed, the > persister would have done its thing. > > > of course, i'm not sure thats the proper way of implementing it, but > as an idea - tell the specific collections that are created for the entities > of a specific query to do something else than the default, it is possible > > > > On Wed, Sep 1, 2010 at 7:49 PM, John Davidson > <[email protected]<mailto:[email protected]>> > wrote: > > > > I think nadav is saying that subselect from NHibernate is an issue, > but the implementation he is proposing will fix that problem > > > John Davidson > > > > On Wed, Sep 1, 2010 at 12:46 PM, Fabio Maulo > <[email protected]<mailto:[email protected]>> > wrote: > > > > > 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]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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 > > > > > > > > > > > > -- > Fabio Maulo > > > > > > > > > -- > Fabio Maulo > > > > > > > -- > Fabio Maulo > > > > > > >
