Linq: how to use specifications against associated objects

Question

I'm using specifications in this kind of form:

public static Expression<Func<User, bool>> IsSuperhero
{
  get
  {
    return x => x.CanFly && x.CanShootLasersFromEyes;
  }
}

Now I can use this specification in the form:

var superHeroes = workspace.GetDataSource<User>().Where(UserSpecifications.IsSuperhero);

But I'm not sure how to use the specification against an associated object like this:

var loginsBySuperheroes = workspace.GetDataSource<Login>().Where(x => x.User [ ??? ]);

Is there a way to do this, or do I need to rethink my implementation of specifications?

Answer 1

Obviously:

var loginsBySuperheroes = workspace.GetDataSource<User>()
  .Where(UserSpecifications.IsSuperhero)
  .SelectMany(x => x.Logins);

This can be fun:

var secretBillionaires = workspace.GetDataSource<User>()
   .Where(UserSpecifications.IsSuperhero)
   .SelectMany(user => user.Logins)
   .Where(LoginSpecifications.IsSecretIdentity)
   .Select(login => login.DayJob)
   .Where(DayJobSpecifications.IsBillionaire)