This relationship goes 4 deep. When it does lazy loading it ends up
running like 500+ queries.
This job can easily be done in 4 queries, and then the content
aggregated.
I have not touched batch size, because its already set, and the number
of records coming back is not the issue.
I have tried fetch but then you end up returning large amounts of
unnecessary data, which is why I want to use futures.
This is supposed work. It's documented as how it works. I just don't
know how to get it to do join type select with QueryOver.
I'm going to try it with the criteria API.
.SetFetchMode("Items", FetchMode.Select) <-- this is pretty much what
I want.
What is subselect fetching?
Is there a way to fetch an entire list of data, instead of one at a
time?
x.Items.Items <-- I want to fill every single item inside that
collection in one sql call instead of it lazy loading each one that I
want.
What I want it to run is:
select A.* from A where A.id = ?
select B.* from B where B.aid = ?
select C.* from C left join B where B.aid = ?
select D.* from D left join C left join B where b.aid = ?
I don't mind joining up to A instead of B. But yeah. Also notice I
don't want every single column, because that's pointless.
On Jan 30, 1:44 pm, Oskar Berggren <[email protected]> wrote:
> 2012/1/30 Brad Laney <[email protected]>:
>
> > Hello.
>
> > I am trying to avoid N+1 and cartesian product when I need to do deep
> > eager loads. I want to do this for performance. It is an EAV type of a
> > data structure.
>
> Is the problem too many queries, or that you absolutely cannot have
> more than one roundtrip to the database?
>
> [...]
>
>
>
> > var r = s.QueryOver<NHMapTest1>()
> > .Where(x => x.Id == id)
> > .Future();
>
> > s.QueryOver<NHMapTest2>()
> > .Where(x => x.Parent.Id == id)
> > .Future();
> > Running r.Single(); returns the entity, but if you do .Items it'll
> > query the DB, even tho they were selected in the 2nd future. Both
> > queries run correctly and return valid results.
>
> When you access the collection, even though a number of objects of the
> collection's member type has been loaded, NH doesn't know they are
> part of the collection, that's why it needs to query again. Looking at
> the child's Parent reference of loaded objects wouldn't be enough,
> since it doesn't know if those are _all_ the children.
>
> Have you set proper batch size on your collections and classes? And
> possibly specify subselect fetching for the collections. With that you
> should be able to rely on lazy fetch, but with a limited number of
> round trips.
>
> /Oskar
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