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POundo/redo with cascading deletions
 

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    <p>I'm trying to implement an undo/redo feature into my application, using the <a href="http://en.wikipedia.org/wiki/Command_pattern" rel="noreferrer">Command Pattern</a>. I'm facing a problem.</p> <p>To illustrate it, let's imagine you can create with my application 2D profiles (as many as you want).</p> <p>From these 2D profiles, you can then create a 3D part with different attributes (name, colour, scale, etc.).</p> <pre><code>+--------------+ +--------------+ +--------------+ | 2D profile A | | 2D profile B | | 2D profile C | +--------------+ +--------------+ +--------------+ | | | | +---------------+ +---------------+ | | 3D Part B | | 3D Part C | | | Colour : blue | | Colour : grey | | | Name : bibi | | Name : foo | | | Scale : 33% | | Scale : 100% | | +---------------+ +---------------+ +--------------+ | 3D Part A | | Colour : red | | Name : aaa | | Scale : 50% | +--------------* </code></pre> <p>When a profile is deleted, all 3D parts which a built on this profile are automaticaly deleted too (when a profile is about to be deleted, a 3D part manager is notified and will delete the obsolete 3D parts. Views are also notified to update the GUI).</p> <p>This is where I'm facing a problem : I'm writing the undo/redo command for deleting a 2D profile, which looks something like this (pseudo-code) :</p> <pre><code>virtual void redo() { m_pProfileList.remove(m_pProfile); // This will automatically delete all 3D parts relying on the deleted 2D profile } virtual void undo() { m_pProfileList.add(m_pProfile); // This will add the 2D profile, but the 3D Parts are lost } </code></pre> <p>As you can see in the code above, removing the 2D profile will automatically delete all 3D parts relying on the removed profile.</p> <p>But when doing undo, re-adding the 2D profile to the list is not enough : the 3D parts are lost.</p> <p>What should I do ? Should the undo/redo command be responsible of taking care of the deletion of the 3D parts (which is something actually done by the 3d part manager) ? This would mean the undo/redo command would also be responsible to notify the views to update the GUI.</p> <p>Or should the undo/redo command create an internal copy of all 3d parts which will be deleted and let the 3d part manager delete the 3D parts ?</p> <p>Or is there another better solution ?</p> <p>Thanks for your help !</p>
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