Migrating entities and parent entities

问题

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.

How can I migrate objects of entity B to a new version of my data model, including the attributes from entity A?

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).

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Edit:

I'm not referring to a regular relationship between two entities, but inheritance:

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Edit 2:

Just to be sure, I created a new project to test with. Herein, I added only the two entities as seen above. In my awakeFromNib I do a fetch request and if no results are returned, I add a new entity:

    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"];

In my second version of the data model, I added a new entity and I enabled automatic migration via

NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];

if (![__persistentStoreCoordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:dict error:&error]) {

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).

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Edit 3: 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:

So, I guess that would make this a bug in Xcode 4.

回答1:

I am not sure what went wrong.

I just created this data model version 1, I hope this gets as close to your case as possible:

Then I created this version 2, no changes to Parent and Child only one new entity:

The I created a mapping model and this is what it automatically suggested:

Let's have a look at the differences:

Only one change: the new entity Neighbour.

Can you post some pics of your situation?

Note This is XCode3

回答2:

Turns out this was a bug in the version of Xcode I was using at the time and was resolved in Xcode 4.2.

来源：https://stackoverflow.com/questions/6129539/migrating-entities-and-parent-entities