Inserting an object into BlockTableRecord.Paperspace

[nshupeFMPE3]

I have this piece of legacy code I'm trying to understand. When I want to insert something into a paperspace Layout I usually use Database.CurrentSpaceId or some other means of finding the Layout object. Then I open the Layout.BlockTableRecord and append the Entity. 

But this code is using BlockTableRecord.Paperspace. I'm familiar with BlockTableRecord.Model, but how does the former work if there are multiple paperspace Layouts?

Document doc = Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;

using (Transaction transaction = db.TransactionManager.StartOpenCloseTransaction())
using(BlockTable bt = transaction.GetObject(db.BlockTableId, OpenMode.ForRead, false, true) as BlockTable)
{
    try
    {
        if (!(db.CurrentSpaceId == bt[BlockTableRecord.PaperSpace]))
        {
            doc.Editor.WriteMessage("\n You must be in paperspace to insert the Loop Schedule.");
            transaction.Abort();
            return;
        }

        Point3d insertPoint = GetInsertPoint();

        Table tb = MakeTableObj(insertPoint);

        using (BlockTableRecord btr =
               transaction.GetObject(bt[BlockTableRecord.PaperSpace], OpenMode.ForWrite, false, true) as
                   BlockTableRecord)
        {
            btr.AppendEntity(tb);
            transaction.AddNewlyCreatedDBObject(tb, true);
        }

        transaction.Commit();
    }
    catch (Exception ex)
    {
        transaction.Abort();
        doc.Editor.WriteMessage($"Error in {nameof(MethodName)}: {ex.Message}");
    }
}

[_gile · Accepted solution]

Hi,

A quick test would have shown you that, when called from a layout tab, PaperSpace refers to the active layout; when called from the model space, PaperSpace refers to the last closed layout, or the first layout tab if none has yet been opened.

In my opinion, unless the active space is a known layout, this property isn't very reliable, in which case I prefer CurrentSpaceId.