[CommandMethod("Test")]
public void Test()
{
Document doc = Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
using (var t = db.TransactionManager.StartTransaction())
{
var cs = db.CurrentSpaceId.GetObject( OpenMode.ForWrite) as BlockTableRecord;
Solid3d acSol3D = new Solid3d();
acSol3D.SetDatabaseDefaults();
acSol3D.CreateBox(1000, 1000, 1000);
cs.AppendEntity(acSol3D);
t.AddNewlyCreatedDBObject(acSol3D, true);
ObjectId id = acSol3D.ObjectId;
t.Commit();
}
}