private IEnumerable <Identity> GetGroupTopicIdsAndDescendants(Identity groupId)
{
var topics = topicByGroup.GetTopicIds(groupId);
foreach (var childTopicId in topics)
{
yield return(childTopicId);
}
var children = childGroupsOfGroup.GetChildrenIds(groupId);
foreach (var child in children)
{
var grandChildren = GetGroupTopicIdsAndDescendants(child);
foreach (var grandChild in grandChildren)
{
yield return(grandChild);
}
}
}
