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POVersion control of a large collection in a database for undo purpose
 

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    <p>In have entities: <code>Collection</code> and <code>Item</code>. Each collection has many items. Both <code>Collection</code> and <code>Item</code> can be edited collaboratively by all users of the application. I have to provide a way to undo changes. Versioning <code>Item</code> records is straightforward, the difficult part is to version the relation between the <code>Collection</code> and <code>Item</code>.</p> <ul> <li>The allowed operations on the collection are: to <strong>insert an item at given position</strong>, to <strong>remove an item</strong> and to change a position of an item within the list (which can be seen as an insert at position + a delete at previous position pair).</li> <li>The insert operation will be called frequently. Sometimes a batch import can insert thousands of items into the collection. I should be able to revert such import and the undo shouldn't take much time to be executed.</li> <li>The list can consist of 20 000 and more items. I rather can't afford to copy the entire collection on each change.</li> <li>I should be able to see the state of a given revision of collection to discover changes that were in the revision. </li> </ul> <p>How to model this in a relational database?</p> <p>I have been thinking about using a multi-valued <a href="http://martinfowler.com/eaaDev/TemporalProperty.html" rel="nofollow noreferrer">Temporal Property</a>. Beside <code>Collection</code> and <code>Item</code> there is a link table with <code>vt_from</code> and <code>vt_to</code> time stamps. Probably I would have to create also a <code>CollectionVersion</code> entity, also with <code>vt_from</code> and <code>vt_to</code> attributes. Those versions would be listed on the "history" page of the collection. However, I haven't came up yet with a general algorithm for reverting changes. Maybe I should have diff lists (added/removed) connected to the <code>CollectionVersion</code> that would be used for that purpose?</p>
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    1. USAdam Dziendziel
    1. USAdam Dziendziel
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