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POCore Data relationship delete rule - Nullify + Cascade
 

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    <p>Entities:</p> <ul> <li>Video</li> <li>Playlist Item</li> <li>Playlist</li> </ul> <p>Relationships:</p> <ul> <li>Video is optional to-many to Playlist Item and the delete rule is nullify</li> <li>Playlist is to-many to at least one Playlist Items and the delete rule is nullify</li> <li>Playlist Item is required to-one for Video and the delete rule is nullify</li> <li>Playlist Item is required to-one for Playlist and the delete rule is nullify</li> </ul> <p>In the Playlist entity, I have not exposed the playlistItem relationship / set. Instead I have a transient undefined attribute called "videos," which is an array of Video entities generated by sorting the set of Playlist Items. There is not a relationship between Playlist and Video entities.</p> <p>I'm having problems when saving a modified Playlist instance in the Managed Object Context.</p> <p><em>From playlist.m (NSManagedObject subclass):</em></p> <pre><code>- (BOOL)validatePlaylistItems:(NSSet **)playlistItems error:(NSError **)outError { NSArray *currentVideos = [self videos]; NSArray *persistedVideos = [self videosFromPlaylistItems]; if ([currentVideos isEqual:persistedVideos]) { return YES; } NSManagedObjectContext *context = [self managedObjectContext]; for (FHPlaylistItem *pi in *playlistItems) { [context deleteObject:pi]; } NSArray *videos = [self primitiveVideos]; NSUInteger count = [videos count]; for (int i = 0; i &lt; count; i++) { FHPlaylistItem *pi = [FHPlaylistItem playlistItemWithVideo:[videos objectAtIndex:i] forIndex:i insertIntoManagedObjectContext:[self managedObjectContext]]; [self addPlaylistItemsObject:pi]; [pi setPlaylist:self]; } return YES; } </code></pre> <p>What I'm trying to accomplish here is only update the set of Playlist Items when the MOC needs to save, as you can see the operation is expensive - O(N * 2). During the first run of the app, the MOC saves just fine. However, subsequent changes to the videos attribute yields in Core Data spewing a bunch of errors:</p> <pre><code>Core Data: annotation: repairing missing delete propagation for to-many relationship playlistItems on object &lt;FHPlaylist: 0x6c27eb0&gt; (entity: Playlist; id: 0x6c26d40 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/Playlist/p19&gt; ; data: { accountID = 0; lastFetched = "2012-03-31 20:05:08 +0000"; name = Featured; playlistID = 1441335931001; playlistItems = ( "0x6c34be0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B2&gt;", "0x6c34320 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p16&gt;", "0x6c310c0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B3&gt;", "0x6c35570 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B5&gt;", "0x6c34ca0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B6&gt;", "0x6c34310 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p8&gt;", "0x6c28a90 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B4&gt;", "0x6c34350 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p29&gt;", "0x6c34220 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p2&gt;", "0x6c34330 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p20&gt;", "(...and 1 more...)" ); playlistType = 0; referenceID = OKFFeaturedPlaylist; shortDescrip = "This is so descriptive! OMG!"; thumbnailURL = nil; videos = "(...not nil..)"; }) with bad fault 0x6c34320 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p16&gt; Core Data: annotation: repairing missing delete propagation for to-many relationship playlistItems on object &lt;FHPlaylist: 0x6c27eb0&gt; (entity: Playlist; id: 0x6c26d40 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/Playlist/p19&gt; ; data: { accountID = 0; lastFetched = "2012-03-31 20:05:08 +0000"; name = Featured; playlistID = 1441335931001; playlistItems = ( "0x6c34be0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B2&gt;", "0x6c310c0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B3&gt;", "0x6c35570 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B5&gt;", "0x6c34ca0 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B6&gt;", "0x6c34310 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p8&gt;", "0x6c28a90 &lt;x-coredata:///PlaylistItem/t9EAFBC87-5E16-4053-984F-881CCD9C1F0B4&gt;", "0x6c34350 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p29&gt;", "0x6c34220 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p2&gt;", "0x6c34330 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p20&gt;", "0x6c34340 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p27&gt;" ); playlistType = 0; referenceID = OKFFeaturedPlaylist; shortDescrip = "This is so descriptive! OMG!"; thumbnailURL = nil; videos = "(...not nil..)"; }) with bad fault 0x6c34310 &lt;x-coredata://BCB69D8E-8393-4A2A-AF5D-0AA1872CE2B4/PlaylistItem/p8&gt; Etc. Etc. Etc. </code></pre> <p>It seems to be the problem lies with the delete rule. The complaint is with a "missing delete propagation," so it seems nullify is the wrong choice. But, why is it wrong? This doesn't make sense to me. The wording of the cascade delete rule in <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html#//apple_ref/doc/uid/TP40001857-SW1" rel="noreferrer">Apple's Core Data Programming Guide</a> makes it seem like I'm going to delete the Video and Playlist objects if I set Playlist Item's delete rule to cascade.</p> <blockquote> <p>Cascade - Delete the objects at the destination of the relationship</p> </blockquote> <p><strike>Furthermore, if I set the relationship from Playlist Item to video &amp; playlist to nil in the fast enumeration loop, Core Data doesn't complain about having to repair the missing delete propagation.</p> <pre><code>for (FHPlaylistItem *pi in *playlistItems) { [pi setVideo:nil]; [pi setPlaylist:nil]; [context deleteObject:pi]; } </code></pre> <p></strike> EDIT: Nope, nil'ing the relationships manually didn't work in all situations. (Maybe no surprise?)</p>
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