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Linq - Join in memory query with fresh query

Posted on 2008-06-16
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Last Modified: 2013-11-26
I would like to join and query an in memory query and a fresh linq query. I will try and explain.

I have a query in memory (CurrentItem.ItemClauses). I need to then join this to a fresh data base query (dbClause.LinksSpecificationClauses) so i can do a contains statement (on clauseid).  Here is my code at the moment but it is very slow.

Thanks


For Each TempClause In CurrentItem.ItemClauses
            Dim SpecID As Int32 = TempClause.SpecificationClauseID
            Dim lsc = (From s In dbClause.LinksSpecificationClauses _
                       Where s.SpecificationClauseID = SpecID).SingleOrDefault
            If lsc.ClauseID = ClauseID Then
                Return True
            End If
        Next

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Question by:suroma
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Expert Comment

by:naspinski
ID: 21799284
are you asking how to make it faster?

Would you be able to make this in to one query?  Or do you have to have it split?  Because right now you have your initials query, which finds x objects, and then you are running x queries.

If you have to keep them split, you have to think of any ways you can programmatically eliminate options that are in your CurrentItem.ItemClauses query before you call the query inside foreach.  Every item you can eliminate before you make the DB call will speed up your program.  

Another option, since it looks like you are running through it for matches is to simply use a .First() to return (if you only need one to return?  it's hard to tell)  That way, you can simply use a query to return the first result that satisfies, eliminating all remaining checks?  Does that make sense?

Can you possibly explain a little better?  Not sure if I am hitting this or not?

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Author Comment

by:suroma
ID: 21799421
I would like to make it into one query but i don't know how to. This is how I would do it if i was just calling it from the database.

Dim result = from ic in dbclause.itemclauses join _
lsc In dbClause.LinksSpecificationClauses on lsc.SpecificationClauseID = ic.SpecificationClauseID where lsc.clauseid = clauseid

However the itemclauses is in memory (CurrentItem.ItemClauses) while i build up the clauses needed before submitting it to the database. I just wondered if there was a way of linking in memory object with the database object?
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Accepted Solution

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naspinski earned 500 total points
ID: 21812565
You can't JOIN them or anything since one is SQL and one isn't, but you can manipulate other objects in the query.

Instead of running through each one with it's own query,  you could get a collection with a single query.  If I am reading this right, you want to know which CurrentItem.ItemClauses (assuming this is an int) matches a SpecificationID (int as well)

The following will return a collection of all the SpecificationIDs that match every TempClause in CurrentItem.ItemClauses

Then you can take that list and do what you want with it.  Much more efficient as it is just one trip:
Dim TrueCases = From s In dbClause.LinkSpecificationClauses Where CurrentItem.ItemClauses.Contains(s.SpecificationClauseID) Select s.SpecificationClauseID
 
'hope this is what you are looking for'
'this will spit them out so you can see if it worked'
Response.Write("<h3>True Cases</h2>")
For Each _case In TrueCases
   Response.Write(_case.ToString() + "<br />")
Next

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Author Closing Comment

by:suroma
ID: 31467681
Thanks for your help and pointing me in the right direction. Problem now solved.
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