Re: [Leopard, workaround] Core Data migration for Tiger files

FROM : Adam Swift
DATE : Tue Nov 06 20:50:18 2007

On Nov 6, 2007, at 7:05 AM, Pierre Bernard wrote:

> Hi!
>
> I am seeing problems with Core Data automatic migration reading 
> files created using Tiger.
>
> The problem is triggered by the fact that Core Data determines the 
> source model to use by looking at the file's metadata. Legacy files 
> my lack the required NSStoreModelVersionHashes value. Unfortunately 
> Core Data currently (9A581) does not try to derive that value from 
> the file's actual content. It just fails to read the file.
>
> My workaround is to let Core Data have a pass at the file. If it 
> fails, I check for the missing NSStoreModelVersionHashes value. If 
> it is indeed missing, I load appropriate metadata from a PLIST file 
> and amend the source file.
>
> Another solution would be to manually instantiate a migration 
> manager with the 1.0 model for source model. In the end I decided 
> against this solution which involves more code. The below solution 
> will work gracefully once the Core Data bug is fixed. I.e. the 
> workaround will never again be called.


There's no way for Core Data to reliably determine the appropriate 
model for a Tiger store, consider that a store may have been created 
by an a run-time data model that was constructed from any number of 
entities from any number of models (or constructed programmatically 
entirely in-memory).

When version hashes are not available, your best bet is to create a 
migration manager with the appropriate inputs.

- adam

> Best,
> Pierre Bernard
> Houdah Software s.à r.l.
>
> - (BOOL)configurePersistentStoreCoordinatorForURL:(NSURL *)url
>                                           ofType:(NSString *)fileType
>                               modelConfiguration:(NSString *)configuration
>                                      storeOptions:(NSDictionary *)storeOptions
>                                             error:(NSError **)error
> {
>     NSMutableDictionary *newStoreOptions;
>     
>     if (storeOptions == nil)
>     {
>         newStoreOptions = [NSMutableDictionary dictionary];
>     }
>     else
>     {
>         newStoreOptions = [[storeOptions mutableCopy] autorelease];
>     }
>     
>     [newStoreOptions setObject:[NSNumber numberWithBool:YES] 
> forKey:NSMigratePersistentStoresAutomaticallyOption];
>     
>     BOOL ok = [super configurePersistentStoreCoordinatorForURL:url
>                                                         ofType:fileType
>                                             modelConfiguration:configuration
>                                                   storeOptions:newStoreOptions
>                                                          error:error];
>     
>     if (!ok) {
>         /*
>          Legacy files created under Tiger may lack necessary metadata.
>          Add the metadata matching 1.0 files and retry.
>          */
>         NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator 
> metadataForPersistentStoreOfType:NSSQLiteStoreType URL:url 
> error:error];
>         id versionHashes = [sourceMetadata 
> objectForKey:@"NSStoreModelVersionHashes"];
>         
>         if (versionHashes == nil) {
>             NSString *legacyMetadataPath = [[NSBundle mainBundle] 
> pathForResource:@"LegacyMetadata" ofType:@"plist"];
>             NSMutableDictionary *metadata = [NSMutableDictionary 
> dictionaryWithContentsOfFile:legacyMetadataPath];
>             
>             [metadata addEntriesFromDictionary:sourceMetadata];
>             
>             if (![NSPersistentStoreCoordinator setMetadata:metadata 
> forPersistentStoreOfType:NSSQLiteStoreType URL:url error:error]) {
>                 return NO;
>             }    
>             
>             *error = nil;
>             ok = [super configurePersistentStoreCoordinatorForURL:url
>                                                           ofType:fileType
>                                               modelConfiguration:configuration
>                                                      storeOptions:newStoreOptions
>                                                             error:error];
>         }
>     }
>     
>     if (ok)
>     {    
>         /*
>          If all went well, update the metadata
>          */
>         
>         NSURL *fileURL = [self fileURL];
>         
>         if (fileURL == nil) {
>             // File URL is null when writing new files
>             fileURL = url;
>         }
>         
>         NSPersistentStoreCoordinator *psc = [[self managedObjectContext] 
> persistentStoreCoordinator];
>         
>         id pStore = [psc persistentStoreForURL:fileURL];
>         
>         /*
>          configurePersistentStoreCoordinatorForURL is called when document 
> reopened
>          Check for existing metadata to avoid overwriting unnecessarily
>          */
>         id existingMetadata = [[psc metadataForPersistentStore:pStore] 
> objectForKey:(NSString *)kMDItemKeywords];
>         
>         if (existingMetadata == nil)
>         {
>             if (![self setMetadataForStoreAtURL:fileURL])
>             {
>                 return NO;
>             }
>         }
>     }
>     
>     return ok;
> }
>
> ---
> Pierre Bernard
> http://www.bernard-web.com/pierre
> http://www.houdah.com
>
>
>
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