public void SetCommunityNodes()
{
if (Communities.Count == 0)
{
throw new Exception("There are no communities");
}
foreach (Community <T> community in Communities)
{
community.CommunityNodes = new HashSet <Node <T> >();
}
foreach (Node <T> node in Nodes)
{
Communities.First(x => x.Id == node.CommunityId).CommunityNodes.Add(node);
}
}