of course i understand how PK queries can resolve proxies without hitting the DB, but collections queries aren't the same.
mother.Children when lazy loaded will result in the following query: from Children c where c.MotherId = X // the id of the father. now you're query does this: from Children c where c.MotherId in (x1,x2,x3,x4) i'm very impressed, yet still uncertain that nhibernate will know that it doesn't need to get the children of mother X after you're query if X is one of the x1...x4 i always thought i have to connect the mothers (the first query) and the children (the second query) my self via memory. are you sure nhibernate does this for me? On Mon, Aug 30, 2010 at 10:13 PM, Diego Mijelshon <[email protected]>wrote: > Yes, it does. > > Let me explain this with a much simpler example: > > var animal = session.Get<Animal>(id); > var mother = session.Get<Animal>(idOfTheMotherOfTheOtherAnimal) > > After running those queries, animal.Mother is a fully initialized proxy. > Collections work pretty much the same. > > The way Identity Map works is that not only you don't need to hit the DB > twice for the same POID; it also means the exact same object is returned. > The same is true for collections: Payment#1234.Receipts exists once and > only once in the session. > > Diego > > > On Mon, Aug 30, 2010 at 16:05, nadav s <[email protected]> wrote: > >> sorry for the ignorance, but the session really knows that the second >> query's results contains the results of the lazy loading query that would of >> been created when accessing the collection? >> >> i thought it works for lazy loaded proxy, because that query is by the >> primary key, so if an object of the same type and the same PK was loaded by >> the same session (or in the second level cache) the proxy lazy loading >> doesn't need to hit the DB, but how does the session know that all of the >> one-to-many associated entities are already loaded? >> >> On Mon, Aug 30, 2010 at 6:04 PM, Diego Mijelshon >> <[email protected]>wrote: >> >>> Yes. >>> >>> Diego >>> >>> >>> >>> On Mon, Aug 30, 2010 at 11:40, Niclas Pehrsson <[email protected]>wrote: >>> >>>> Even if it is better to use DTO's, I want my receipts to have their >>>> list with payments and receipt entries. >>>> So in this solution each receipt will have their receiptentries and >>>> payments loaded, and reachable from receipt.Payments? >>>> On Aug 30, 3:43 pm, Diego Mijelshon <[email protected]> wrote: >>>> > Pseudocode: >>>> > >>>> > var receipts = LinqCriteriaSqlOrHqlQueryForReceiptsOnly() >>>> > .FilteringByIsNotSynchronizedAndIsClosed() >>>> > .InAnyOrderThatYouWant() >>>> > .SetMaxResults(200) // or .Take(200) for Linq >>>> > .List<Receipt>() >>>> > var ids = (from receipt in receipts select receipt.Id).ToList(); >>>> > var irrelevant = QueryForReceiptsFetchingPayments() >>>> > .FilteringByIdIn(ids) >>>> > .List() >>>> > var irrelevantToo = QueryForReceiptsFetchingEntries() >>>> > .YouGetTheIdea() >>>> > .YouCanCombineTheseTwoQueriesWithFuture() >>>> > >>>> > Now, if you are going to use WFC, it's better to create DTOs, >>>> regardless of >>>> > how you do the queries. >>>> > >>>> > Diego >>>> > >>>> > On Mon, Aug 30, 2010 at 05:48, Niclas Pehrsson <[email protected]> >>>> wrote: >>>> > > Well its a lot. >>>> > >>>> > > Receipt has two collections, receipt entries and payments. >>>> > > I want to load top 200 where the receipts is closed and not >>>> > > synchronized. >>>> > > The entities will be sent over wcf so lazyloading isn't anything to >>>> > > use it is best to load them all at the same time. >>>> > > We are using NHibernate 2.1 right now. >>>> > >>>> > > Receipt.IsSynchronized >>>> > > Receipt.IsClosed >>>> > > Receipt.Payments >>>> > > Receipt.Entries >>>> > >>>> > > How would I do this on the most efficient way? >>>> > >>>> > > On Aug 28, 12:55 pm, Diego Mijelshon <[email protected]> >>>> wrote: >>>> > > > ONE QUERY PER COLLECTION, not ONE QUERY PER COLLECTION PER RECORD. >>>> > > > If you have one filtered query with two collections, that's 3 >>>> queries >>>> > > TOTAL, >>>> > > > regardless of the record count. >>>> > >>>> > > > Future allows you to reduce the roundtrips (the number of queries >>>> is >>>> > > still >>>> > > > the same), but you can't combine the first query and the others if >>>> you're >>>> > > > paging. >>>> > > > You can still use it for queries other than the first, which >>>> brings the >>>> > > > roundtrip count to 2 regardless of how many collections or records >>>> you >>>> > > are >>>> > > > loading. >>>> > >>>> > > > Diego >>>> > >>>> > > > On Sat, Aug 28, 2010 at 04:55, Niclas Pehrsson < >>>> [email protected]> >>>> > > wrote: >>>> > > > > Well that means a lot of queries if MaxSize is 200. >>>> > > > > But maybe it is the only way to do it. >>>> > >>>> > > > > Are there any example of this scenario with Criterion? >>>> > > > > I guess the use of Future is needed, you want to get the root >>>> entity >>>> > > > > loaded with its collections as result. >>>> > >>>> > > > > On Aug 27, 8:08 pm, Diego Mijelshon <[email protected]> >>>> wrote: >>>> > > > > > The answer is right there: "two totally separate queries, >>>> first to >>>> > > get >>>> > > > > just >>>> > > > > > the entities, then to load the related associations" >>>> > >>>> > > > > > First, one paged query without fetching the collections, then >>>> one >>>> > > query >>>> > > > > per >>>> > > > > > collection, filtering with the Ids of the first query. >>>> > >>>> > > > > > Diego >>>> > >>>> > > > > > On Fri, Aug 27, 2010 at 09:49, Niclas Pehrsson < >>>> [email protected]> >>>> > > > > wrote: >>>> > > > > > > Well it wont work :( >>>> > >>>> > > > > > > Ayende repsonded to an comment with this >>>> > > > > > > "SetMaxResults, but that might cause issues with the >>>> loading. >>>> > > > > > > At that point, I might want to execute two totally separate >>>> > > queries, >>>> > > > > > > first to get just the entities, then to load the related >>>> > > associations. >>>> > > > > > > " >>>> > >>>> > > > > > > So how can I solve this? >>>> > > > > > > Its a bit annoying, I want to load 200 hundred of thousands, >>>> and I >>>> > > > > > > want to avoid 200+200 select queries. >>>> > > > > > > Any other approaches? >>>> > >>>> > > > > > > On Aug 26, 3:03 pm, Diego Mijelshon <[email protected] >>>> > >>>> > > wrote: >>>> > > > > > > > SetMaxResults and SetFetchMode on _collections_ don't get >>>> along. >>>> > >>>> > > > > > > > Suggested read: >>>> > >>>> > > >>>> http://ayende.com/Blog/archive/2010/01/16/eagerly-loading-entity-asso. >>>> > > > > .. >>>> > >>>> > > > > > > > Diego >>>> > >>>> > > > > > > > On Thu, Aug 26, 2010 at 04:50, Niclas Pehrsson < >>>> > > [email protected]> >>>> > > > > > > wrote: >>>> > > > > > > > > Hi I have an query that looks like this. >>>> > >>>> > > > > > > > > Return (From receipt In _session.Linq(Of >>>> > > > > > > > > PointOfSale.Receipt)() _ >>>> > > > > > > > > Where receipt.IsClosed >>>> AndAlso Not >>>> > > > > > > > > receipt.IsSynchronized _ >>>> > > > > > > > > Select receipt).Take(25).ToList() >>>> > >>>> > > > > > > > > Or >>>> > > > > > > > > Dim criterion = _session.CreateCriteria(Of >>>> Receipt) >>>> > > > > > > > > ().SetMazSize(25).Add(Expression.Eq("IsClosed", True)) _ >>>> > > > > > > > > .Add(Expression.Eq("IsSynchronized", >>>> False)) _ >>>> > > > > > > > > .SetFetchMode("Payments", >>>> FetchMode.Eager) _ >>>> > > > > > > > > .SetFetchMode("ReceiptEntry", >>>> FetchMode.Eager) >>>> > >>>> > > > > > > > > 'Return criterion.List(Of >>>> PointOfSale.Receipt)() >>>> > >>>> > > > > > > > > Both of them first asks the database för the first query >>>> > > options >>>> > > > > > > > > IsClosed and Not IsSynchronized, and then It creates an >>>> select >>>> > > N+1 >>>> > > > > for >>>> > > > > > > > > each element. 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