Something like this, perhaps:

var aRootApart = Umbraco.GetContentById(anIdForTheNode);
if (aRootApart != null) {
  var aRootApartChildrenIds = aRootApart.AllChildIds(); 
} 

Couple of notes. You say "siblings" but refer to "children" (i.e. "under a node") - which should it be, since siblings of a root node would be other root nodes? When using Umbraco.Cms.Web.Model.Content to harness the xxxIds methods then you can get 'bad' data back; that is, `GetContentById` can return null because the Ids can contain those referencing no longer published (or even no longer existing) content.

Lastly, I use `AllChildIds` yet I have no idea if that actually exists; it should be exposed as an extension method but I can't recall the type, can't find the source file nor documentation. It will be something of this sort. You could also, of course, use `GetDynamicContentById` and use `Children`.

Thanks for the reply Grant. Your answer has helped me move on. I will clarify what I am trying to achieve

Here is the structure

-Content

    -Root 1

        -Root1 Node 1

    -Root 2

        -Root 2 Node 1

        -Root 2 Node 2

From within Root 1 Node 1 I want to list the contents of Root 2. i.e. the contents of the sibling of the root node for the tree I am currently in.

I have been able to do this using the answer above but this requires me to know the id of Root 2. Ideally I would be able find this using the alias or perhaps do the same thing with yet another root node i.e. Root 3

Richard,

If you're within a RenderViewPage then you could possibly do something like this (untested):

var matches = Hive.QueryContent().Where(c => c["someAlias"] == "someAliasValue");

Give that a shot and play around with it.

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