Copying more complex structures of objects

[--Fragman--]

Hello all,

I'm creating some kind of object oriented drawing program, my classes
consist of points, lines, quads, etc...
Right now I'm implementing undo/redo and copy/paste functionality.
For that I need to create deep copies of my objects, but set some
property fields to null in some cases.
For example I have an attachment feature which attaches one point of a
line to a point of another shape.
For that I store a reference to an attachment point for each Line point
in the line class and a children array list in each shape.

My question now is, how to copy a list of shapes and not copy the
attachment parents which are not on this list?
And how to copy the cross link between children array and reference to
attach point?

I draw some simple sketch to visualize this:
http://fragman.seriouszone.com/bilder/copying.PNG

I don't really know how to make sure nothing gets copied more than once
and that all links get updated.

[--Fragman--]

I was able to solve this by going through the objects two times, first
linking them to the old objects and in second loop checking for objects
pointing to the objects this object was copied from...yeh kinda hard to
explain...