/// <summary>
/// Gets or creates a "actor".
///
/// In this schema, an actor is a "person" vertex with an incoming "actor" edge from a "movie" vertex. This step
/// therefore assumes that the incoming stream is a "movie" vertex and actors will be attached to that. This step
/// checks for existence of the "actor" edge first before adding and if found will return the existing one. It
/// further ensures the existence of the "person" vertex as provided by the {@link #person(String, String)}
/// step.
/// </summary>
public static GraphTraversal <S, Vertex> Actor <S, E>(this GraphTraversal <S, E> t, string personId, string name)
{
// no validation here as it would just duplicate what is happening in person().
//
// as mentioned in the javadocs this step assumes an incoming "movie" vertex. it is immediately labelled as
// "^movie". the addition of the caret prefix has no meaning except to provide for a unique labelling space
// within the DSL itself.
return(t.As("^movie").
Coalesce <Vertex>(__KillrVideo.Actors().Has(VertexPerson, personId),
__KillrVideo.Person(personId, name).AddE(EdgeActor).From("^movie").InV()));
}