Comparison operators not supported for type 'System.Linq.IQueryable`1[System.Int32]'

Question

Hi Geeks,

I met a issue with LTS My code as below:

return from p in _db.Companies
where p.Deleted == false &&
(from q in _db.Contacts_Companies
where q.ContactId == contactId && q.Deleted == false
select q.CompanyId).Equals(p.Id)
select p;

I know the issue comes from the CompanyId.Equals(Id) they are both Int32, but I am a bit confused that Int32 cannot be compared? If I use Contains, it wont match my requirement.

How could I overcome this issue?

Answer 1

Your "inner" query is selecting a list of company IDs (even if that list only contains one item), so it's not correct to compare it to a single value.

Try selecting only the first item:

return from p in _db.Companies 
       where !p.Deleted && (
           from q in _db.Contacts_Companies 
           where q.ContactId == contactId && !q.Deleted 
           select q.CompanyId).FirstOrDefault() == p.Id
       select p;

Answer 2

The problem originates with your sub-query:

from q in _db.Contacts_Companies
where q.ContactId == contactId && q.Deleted == false
select q.CompanyId

This doesn't return an int - it returns (as shown in your error message) IQueryable<int>.

Perhaps you're caught up on the deferred execution semantics of linq?

Anyway, to solve this you need to convert from the IQueryable<int> to a simple int. Since you're always expecting exactly one result, I'd suggest adding .First():

return from p in _db.Companies
where p.Deleted == false &&
(from q in _db.Contacts_Companies
where q.ContactId == contactId && q.Deleted == false
select q.CompanyId).First().Equals(p.Id)
select p;