A service for deletions with model changes

Josh Moore, April/2007

Note (Jan/2008): A simpler, stateless DeleteService? (IDelete) has been added, as outlined by #857.

  public interface DeleteTransaction extends StatefulServiceInterface {

    void addObject(IObject o); // Same semantics as IUpdate.deleteObject
    void addGraph(IObject graph); // Tries to delete all passed items. Unload where needed
    void addCollection(java.util.Collection<IObject> coll); // As previous
    void addAllByQuery(String query, ome.params.Parameters p); // Same query string as IQuery
    IObject[] listObjects();

    void purge();
    void isPurge();
    void useTrashCan();
    void isUseTrashCan();
    void optionallyUseTrashCan();
    void isOptionallUseTrashCan();

    /** 
     * Executes the commit, and returns the number of elements that were actually deleted.
     */
    int commit();

  }

The reason for having a stateful service is that often one would want to check what is going to be deleted before doing so:

   IObject[] objs = iQuery.findAllByQuery("some.long.query",null);
   // check objs
   iDelete.deleteAllByQuery("some.long.query",null);

This unfortunately is tedious and hits the db way too often. Instead, we can encapsulate as a stateful service.

Implementation

• Partial ordering -- ExtendedMetadata? would offer a Java comparator via getPartialOrdering() which would allow a list of objects to be ordered by class for individual deletion
• GarbageCollector? -- checks for original files, pixel files, etc. that no longer have an entry in the db, and expunges them. This frees us from having to worry writing "handlers" which intercept delete actions, etc.
• If the "trashCan" logic from the interface is to be implemented, we'll have to have a "hidden" flag on all IObject entities (IObject.isHidden()) which clients would be required to check.

Issues

• Thumbnails and other 3rd person "annotations" which prevent entities from being deleted via foreign key constraints -- The solutions I see are:
  1. Keep the the thumbnails as they are currently; an admin has to delete them.
  2. Give thumbnails a special status ("attribute") so they can be deleted. See proposals/Attributes
  3. Rework the security system; changing our concept of "links"