迁移实体和父实体 [英] Migrating entities and parent entities

问题描述

我有一个具有两个属性的实体A.实体B具有A作为父对象，并具有其他3个属性.新版本中的更改不会影响实体A和实体B.

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.

如何将实体B的对象迁移到数据模型的新版本，包括来自实体A的属性?

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

我尝试使用两个实体映射:一个用于A，一个用于B，但是'A属性'并未迁移.或者，我将A的属性添加到映射中以迁移B，但是在那里我无法选择正确的属性(在Xcode 4中).

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).

我不是指两个实体之间的常规关系，而是继承:

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

可以肯定的是，我创建了一个新项目进行测试.在这里，我仅添加了两个实体，如上所示.在我的 awakeFromNib 中，执行获取请求，如果未返回任何结果，则添加一个新实体:

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"];

在第二个数据模型版本中，我添加了一个新实体，并通过启用了自动迁移

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]) {

确实确实发生了迁移，并且成功迁移了BankDebitAccount的三个属性.Account中的currentBalance属性重置为0，并且name属性在XML文件中不再可见(因此等于nil).

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).

我只是尝试在Xcode 3(.2.4)中打开这个新创建的测试项目.当我在其中打开映射模型并选择子实体的映射时，实际上可以为父实体的属性添加一个属性映射:

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:

所以，我想这会使它成为Xcode 4中的一个错误.

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

推荐答案

结果证明这是我当时使用的Xcode版本中的一个错误，并已在Xcode 4.2中解决.

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

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