Question

Is there an alternative to using .Contains() to select objects in Entity Framework that exist in a specified list? Contains() works great if your list is small, however once you start getting a few thousands items the performance is terrible.

return (from item in context.Accounts
        where accountIdList.Contains(item.AccountId)
        select item).ToList();

I’m using EF 4.0, .Net Framework 4.0, and SQL Server 2005. I’m not opposed to a SQL solution either since the query that EF generates only takes a second to run on SQL for about 10k items.

Answer 1

I found an alternative that runs in about a second using a SQL Stored Procedure and a comma-delimited string for the parameter. Much better than the 5+ minutes EF was taking using .Contains()

It is run from my code using the following:

string commaDelmitedList = string.Join(",", accountIdList);
return context.GetAccountsByList(commaDelmitedList).ToList();

The StoredProcedure (simplified) looks like this:

SELECT *
FROM   Accounts as T1 WITH (NOLOCK)
INNER JOIN (
    SELECT Num FROM dbo.StringToNumSet(@commaDelimitedAccountIds, ',')
) as [T2] ON [T1].[AccountId] = [T2].[num]

And the User-Defined function dbo.StringToNumSet() looks like this:

CREATE FUNCTION [dbo].[StringToNumSet] (
 @TargetString  varchar(MAX),
 @SearchChar varchar(1)
 )
RETURNS @Set TABLE (
 num int not null
 )
AS
BEGIN
 DECLARE @SearchCharPos  int,  @LastSearchCharPos int
 SET @SearchCharPos = 0
 WHILE 1=1
 BEGIN
  SET @LastSearchCharPos = @SearchCharPos
  SET @SearchCharPos = CHARINDEX( @SearchChar, @TargetString, @SearchCharPos + 1 )
  IF @SearchCharPos = 0
  BEGIN
   INSERT @Set( num ) VALUES ( SUBSTRING( @TargetString, @LastSearchCharPos + 1, DATALENGTH( @TargetString ) ) )
   BREAK
  END
  ELSE
   INSERT @Set( num ) VALUES ( SUBSTRING( @TargetString, @LastSearchCharPos + 1, @SearchCharPos - @LastSearchCharPos - 1 ) )
 END
 RETURN
END