Adding a Join to an existing var: not a sequence

Question

(SubSonic) I have this initial declaration to do a simple join.

var ji = from pli in PriceListItem.All( )
         join ci in CatalogItem.All( ) on pli.CatalogItemID equals ci.CatalogItemID
         select new { pli = pli, ci = ci };

Before executing the sql, under some circumstance, I want to add a join to an in-memory list. When I code

    var Results =
        from SID in priceListItemID
        join pli in PriceListItem.All( ) on SID equals pli.PriceListItemID
        join ci in CatalogItem.All( ) on pli.CatalogItemID equals ci.CatalogItemID
        select new { pli = pli, ci = ci };

I get a SQL query for the CatalogItem table, then one for the PriceListItem table, then the joins (including the in-memory list) occur in code.

Trying to avoid this, my code is this:

List<Guid> priceListItemID = new List<Guid>( );

...some code follows that fills the list, then

ji = ji.Join( priceListItemID, p => p.pli.PriceListItemID, i => i, ( p, i ) => p );

then, eventually,

foreach( var r in ji )

Without the additional join, this is OK. Adding a where clause (instead of the join),

IEnumerable<Guid> guids = priceListItemID;
ji = ji.Where( p => guids.Contains( p.pli.PriceListItemID ) );

is also OK. However, with the join, there comes the exception: "the expression of type 'System.Collections.Generic.IEnumerable`1[System.Guid]' is not a sequence.