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POMigrating entities and parent entities
 

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  1. POMigrating entities and parent entities
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    <p>I have an entity A which has two attributes. Entity B has A as parent and has an additional 3 attributes. The changes in the new version don't affect entities A and B.</p> <p>How can I migrate objects of entity B to a new version of my data model, including the attributes from entity A?</p> <p>I tried using two entity mappings: one for A and one for B, but 'A attributes' aren't migrated. Alternatively I would add A's attributes to the mapping to migrate B, but there I can't selected the right attributes (in Xcode 4).</p> <hr> <p><em>Edit:</em></p> <p>I'm not referring to a regular relationship between two entities, but inheritance: <img src="https://i.stack.imgur.com/sumKG.png" alt="Image showing client and parent entity"></p> <hr> <p><em>Edit 2:</em></p> <p>Just to be sure, I created a new project to test with. Herein, I added only the two entities as seen above. In my <code>awakeFromNib</code> I do a fetch request and if no results are returned, I add a new entity:</p> <pre><code> NSManagedObject *newAccount = [[NSManagedObject alloc] initWithEntity:entityDesc insertIntoManagedObjectContext:[self managedObjectContext]]; // Account [newAccount setValue:@"TheName" forKey:@"name"]; [newAccount setValue:[NSDecimalNumber decimalNumberWithMantissa:5 exponent:2 isNegative:NO] forKey:@"currentBalance"]; // BankDebitAccount [newAccount setValue:@"TheAccountNumber" forKey:@"accountNumber"]; [newAccount setValue:@"TheBankName" forKey:@"bankName"]; [newAccount setValue:[NSDecimalNumber decimalNumberWithMantissa:6 exponent:1 isNegative:YES] forKey:@"openingBalance"]; </code></pre> <p>In my second version of the data model, I added a new entity and I enabled automatic migration via</p> <pre><code>NSMutableDictionary *dict = [NSMutableDictionary dictionary]; [dict setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption]; if (![__persistentStoreCoordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:dict error:&amp;error]) { </code></pre> <p>The migration does indeed happen, and the three properties from BankDebitAccount successfully are migrated. The currentBalance property from Account is reset to 0 and the name property isn't visible in the XML file anymore (and thus, is equal to nil).</p> <hr> <p><em>Edit 3:</em> I just tried opening this newly made test project in Xcode 3(.2.4). When I open the mapping model in there and select my child entity's mapping, I can actually add an attribute mapping for the parent's attributes:</p> <p><img src="https://i.stack.imgur.com/8MCQa.png" alt="Child&#39;s entity mapping in Xcode 3"></p> <p>So, I guess that would make this a bug in Xcode 4.</p>
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