Linq Subquery Where Clause - linq

Question

I need some help with thsi linq query. It shoudl be fairly simple, but it is kicking my butt.
I need to use a subquery to filter out data from the main query, but every path I have tried to use results in failure.
The subquery by itself looks like this.
int pk = (from c in context.PtApprovedCertifications
where c.FkosParticipant == 112118 &&
(!excludedActionTypes.Contains(c.FkMLSosCodeActionType)) &&
c.EffectiveDate <= DateTime.Now &&
c.FkptApprovedCertificationVoidedBy == null
orderby c.EffectiveDate descending,c.PK descending
select c.PK).FirstOrDefault();
This works as expected but as you can see I plugged in the number 112118. This should be the primary key from main query.
The combined query I've been working on looks like this.
IQueryable<PtAMember> result = (from p in context.PtAMembers
where (p.FkptACertification == (from c in context.PtApprovedCertifications
where c.FkosParticipant == p.PtApprovedCertification.OsParticipant.PK &&
(!excludedActionTypes.Contains(c.FkMLSosCodeActionType)) &&
c.EffectiveDate <= DateTime.Now &&
c.FkptApprovedCertificationVoidedBy == null
orderby c.EffectiveDate descending, c.PK descending
select c.PK).FirstOrDefault()) &&
(p.LastName.ToLower().Contains(param.ToLower()) ||
p.FirstName.ToLower().Contains(param.ToLower()) ||
p.SocialSecurityNumber.Contains(param))
select p).Distinct().OrderBy(PtAMembers => PtAMembers.LastName).ThenBy(PtAMember => PtAMember.FirstName);
This results in an error though. Any help in solving this conundrum would greatly appreciated.
Thanks!

Answer 1

How about turning your subquery into a lookup function:
Func<int, int> pkLookup = n => (from c in context.PtApprovedCertifications
where c.FkosParticipant == n &&
(!excludedActionTypes.Contains(c.FkMLSosCodeActionType)) &&
c.EffectiveDate <= DateTime.Now &&
c.FkptApprovedCertificationVoidedBy == null
orderby c.EffectiveDate descending,c.PK descending
select c.PK).FirstOrDefault();
then using that in your main query.