Question

Working from http://help.dataobjects.net/##DataObjects.Net%20v4.5/html/bda59613-172c-427f-86fc-046ccd7e4253.htm I put together some code to try and solve an optimization problem. E.g.

Dim parentsLinq As IEnumerable(Of Parent) =
    From p As Parent In Xtensive.Orm.Session.Demand().Query.All(Of Parent)()
    Select p
    Take 10

parentsLinq = parentsLinq.Prefetch(Function(p As Parent) p.Children)
Dim parentsList As List(Of Parent) = parentsLinq.ToList()

Profiling this with the Red Gate ANTS performance profiler shows that this results in 2 SQL database calls. The first is for SELECT TOP 10 Parents, which is fine. The second is 10 separate queries for Children WHERE parentID=@p1_0 through parentID=@p1_10. Is there any way to make DataObjects use a single query (e.g. using JOIN) to prefetch the children? The database is running in Legacy_Validate mode.

Accepted Answer

1

DataObjects.Net never uses joins for prefetch. It groups the entities to fetch and uses single query with IN operator. Prefetching of EntitySets currently does not have such grouping optimization thus this is expected behaviour.

answered Dec 13 '12 at 03:43

Denis Krjuchkov
1793●2●5

Thanks for the explanation. :)

(Dec 13 '12 at 08:49) GigMastersTech

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