LINQ correlated subqueries

Question

Starting with the next entities definition:

Public Class Certificate{
  public  ID as int;
}

Public Class Authority{
  ID int;
  Certificates IEnumerable<Certificate>;
}

My function recives 2 collections: IEnumerable<Certificate> and IEnumerable<Authority> . I need to select the Authorities which Certificates collection has at least one Certificate in the IEnumerable<Certificate> input parameter.

My firt implementation is enumerating the IEnumerable<Certificate> and selecting the Authority using a Where(predicate) .

Public IEnumerable<Authority> SelectAuthorities(authList IEnumerable<Authority>, certList IEnumerable<Certificate>){

  foreach (Certificate loadedCert in certList) {
    yield return auth.Where(a => a.Certificados.Any(c1 => c1.IDCert == loadedCert.IDCert));
  }  

}

I think there must be a way to avoid the for loop using a more complex linq correlated subquery (I feel it in the "force") but I can't find it.

Can anybody help?

Answer 1

You can use double Any to avoid loop:

authList.Where(a => a.Certificados
                     .Any(c1 => certList.Any(c2 => c1.IDCert == c2.IDCert)));