/// <summary>
/// Gets or creates a "person".
///
/// This step first checks for existence of a person given their identifier. If it exists then the person is
/// returned and their "name" property updated. It is not possible to change the person's identifier once it is
/// assigned (at least as defined by this DSL). If the person does not exist then a new person vertex is added
/// with the specified identifier and name.
/// </summary>
public static GraphTraversal <S, Vertex> Person <S, E>(this GraphTraversal <S, E> t, string personId, string name)
{
if (string.IsNullOrEmpty(personId))
{
throw new ArgumentException("The personId must not be null or empty");
}
if (string.IsNullOrEmpty(name))
{
throw new ArgumentException("The name of the person must not be null or empty");
}
return(t.Coalesce <Vertex>(__.V().Has(VertexPerson, KeyPersonId, personId),
__.AddV(VertexPerson).Property(KeyPersonId, personId)).
Property(KeyName, name));
}