Linq: how to use specifications for related objects

Question

I use specifications in the form of this kind:

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 for a related object as follows:

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

Is there a way to do this, or do I need to review my specification implementation?

Answer 1

Obviously:

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

This might be interesting:

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

Answer 2

, Expression<Func<Login, bool>>, , IsSuperhero . , Expression.Invoke "" (IsSuperhero ), .

, , . , LINQ, LINQ to Entities, " ". , "" "invoked" , .

, LINQKit, :

#region LINQKit Magic

Expression<Func<Login, bool>> predicate = login => IsSuperHero.Invoke(login.User);
var expandedPredicate = predicate.Expand(); 

#endregion LINQKit Magic

var loginsBySuperheroes = workspace.GetDataSource<Login>().Where(expandedPredicate);

Answer 3

, :

var loginsBySuperheroes = GetLogins().Where(l => IsSuperhero.Compile().Invoke(l.User));

:

var f = IsSuperhero.Compile();
var loginsBySuperheroes = GetLogins().Where(l => f(l.User));

Answer 4

You can create your own custom QueryProvider, as described in detail here: http://msdn.microsoft.com/en-us/library/bb546158.aspx